Standardized Glossary
This glossary is intended to be a comprehensive, standardized list of Kubernetes terminology. It includes technical terms that are specific to Kubernetes, as well as more general terms that provide useful context.
Filter terms according to their tags
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The inner components of Kubernetes.
Related to Kubernetes open-source development.
A resource type that Kubernetes supports by default.
Supported customizations of Kubernetes.
Relevant for a first-time user of Kubernetes.
How Kubernetes components talk to each other (and to programs outside the cluster).
Starting and maintaining Kubernetes.
Keeping Kubernetes applications safe and secure.
How Kubernetes applications handle persistent data.
Software that makes Kubernetes easier or better to use.
Represents a common type of Kubernetes user.
Applications running on Kubernetes.
Architecture
Community
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Extension
Fundamental
Networking
Operation
Security
Storage
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Click on the [+] indicators below to get a longer explanation for any particular term.
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Admission ControllerLINK
A piece of code that intercepts requests to the Kubernetes API server prior to persistence of the object.
[+]Admission controllers are configurable for the Kubernetes API server and may be “validating”, “mutating”, or both. Any admission controller may reject the request. Mutating controllers may modify the objects they admit; validating controllers may not.
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Aggregation LayerLINK
The aggregation layer lets you install additional Kubernetes-style APIs in your cluster.
[+]When you’ve configured the Kubernetes API ServerControl plane component that serves the Kubernetes API. to support additional APIs, you can add
APIServiceobjects to “claim” a URL path in the Kubernetes API. -
AnnotationLINK
A key-value pair that is used to attach arbitrary non-identifying metadata to objects.
[+]The metadata in an annotation can be small or large, structured or unstructured, and can include characters not permitted by labels. Clients such as tools and libraries can retrieve this metadata.
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API GroupLINK
A set of related paths in Kubernetes API.
[+]You can enable or disable each API group by changing the configuration of your API server. You can also disable or enable paths to specific resources. API group makes it easier to extend the Kubernetes API. The API group is specified in a REST path and in the
apiVersionfield of a serialized object.- Read API Group for more information.
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API serverLINKAlso known as:kube-apiserver
The API server is a component of the Kubernetes control planeThe container orchestration layer that exposes the API and interfaces to define, deploy, and manage the lifecycle of containers. that exposes the Kubernetes API. The API server is the front end for the Kubernetes control plane.
[+]The main implementation of a Kubernetes API server is kube-apiserver. kube-apiserver is designed to scale horizontally—that is, it scales by deploying more instances. You can run several instances of kube-apiserver and balance traffic between those instances.
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App ContainerLINK
Application containers (or app containers) are the containersA lightweight and portable executable image that contains software and all of its dependencies. in a podThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. that are started after any init containersOne or more initialization containers that must run to completion before any app containers run. have completed.
[+]An init container lets you separate initialization details that are important for the overall workloadA workload is an application running on Kubernetes. , and that don’t need to keep running once the application container has started. If a pod doesn’t have any init containers configured, all the containers in that pod are app containers.
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Application ArchitectLINK
A person responsible for the high-level design of an application.
[+]An architect ensures that an app’s implementation allows it to interact with its surrounding components in a scalable, maintainable way. Surrounding components include databases, logging infrastructure, and other microservices.
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ApproverLINK
A person who can review and approve Kubernetes code contributions.
[+]While code review is focused on code quality and correctness, approval is focused on the holistic acceptance of a contribution. Holistic acceptance includes backwards/forwards compatibility, adhering to API and flag conventions, subtle performance and correctness issues, interactions with other parts of the system, and others. Approver status is scoped to a part of the codebase. Approvers were previously referred to as maintainers.
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CIDRLINK
CIDR (Classless Inter-Domain Routing) is a notation for describing blocks of IP addresses and is used heavily in various networking configurations.
[+]In the context of Kubernetes, each NodeA node is a worker machine in Kubernetes. is assigned a range of IP addresses through the start address and a subnet mask using CIDR. This allows Nodes to assign each PodThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. a unique IP address. Although originally a concept for IPv4, CIDR has also been expanded to include IPv6.
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CLA (Contributor License Agreement)LINK
Terms under which a contributorSomeone who donates code, documentation, or their time to help the Kubernetes project or community. grants a license to an open source project for their contributions.
[+]CLAs help resolve legal disputes involving contributed material and intellectual property (IP).
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Cloud Controller ManagerLINK
Cloud Controller Manager is an alpha feature in 1.8. In upcoming releases it will be the preferred way to integrate Kubernetes with any cloud.
[+]Kubernetes v1.6 contains a new binary called cloud-controller-manager. cloud-controller-manager is a daemon that embeds cloud-specific control loops. These cloud-specific control loops were originally in the kube-controller-manager. Since cloud providers develop and release at a different pace compared to the Kubernetes project, abstracting the provider-specific code to the cloud-controller-manager binary allows cloud vendors to evolve independently from the core Kubernetes code.
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Cloud Native Computing Foundation (CNCF)LINK
The Cloud Native Computing Foundation (CNCF) builds sustainable ecosystems and fosters a community around projects that orchestrate containers as part of a microservices architecture.
Kubernetes is a CNCF project.
[+]The CNCF is a sub-foundation of the Linux Foundation. Its mission is to make cloud native computing ubiquitous.
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Cloud ProviderLINKAlso known as:Cloud Service Provider
A business or other organization that offers a cloud computing platform.
[+]Cloud providers, sometimes called Cloud Service Providers (CSPs), offer cloud computing platforms or services.
Many cloud providers offer managed infrastructure (also called Infrastructure as a Service or IaaS). With managed infrastructure the cloud provider is responsible for servers, storage, and networking while you manage layers on top of that such as running a Kubernetes cluster.
You can also find Kubernetes as a managed service; sometimes called Platform as a Service, or PaaS. With managed Kubernetes, your cloud provider is responsible for the Kubernetes control plane as well as the nodesA node is a worker machine in Kubernetes. and the infrastructure they rely on: networking, storage, and possibly other elements such as load balancers.
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ClusterLINK
A set of machines, called nodes, that run containerized applications managed by Kubernetes. A cluster has at least one worker node and at least one master node.
[+]The worker node(s) host the pods that are the components of the application. The master node(s) manages the worker nodes and the pods in the cluster. Multiple master nodes are used to provide a cluster with failover and high availability.
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Cluster OperationsLINKActivities such as upgrading the clusters, implementing security, storage, ingress, networking, logging and monitoring, and other operations involved in managing a Kubernetes cluster. [+]
Activities such as upgrading the clusters, implementing security, storage, ingress, networking, logging and monitoring, and other operations involved in managing a Kubernetes cluster.
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Cluster OperatorLINK
A person who configures, controls, and monitors clusters.
[+]Their primary responsibility is keeping a cluster up and running, which may involve periodic maintenance activities or upgrades.
Note: Cluster operators are different from the Operator pattern that extends the Kubernetes API. -
Code ContributorLINK
A person who develops and contributes code to the Kubernetes open source codebase.
[+]They are also an active community memberA continuously active contributor in the K8s community. who participates in one or more Special Interest Groups (SIGs)Community members who collectively manage an ongoing piece or aspect of the larger Kubernetes open source project. .
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ConfigMapLINK
An API object used to store non-confidential data in key-value pairs. Can be consumed as environment variables, command-line arguments, or config files in a volumeA directory containing data, accessible to the containers in a pod. .
[+]Allows you to decouple environment-specific configuration from your container imagesA lightweight and portable executable image that contains software and all of its dependencies. , so that your applications are easily portable. When storing confidential data use a Secret.
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Container Environment VariablesLINK
Container environment variables are name=value pairs that provide useful information into containers running in a Pod.
[+]Container environment variables provide information that is required by the running containerized applications along with information about important resources to the ContainersA lightweight and portable executable image that contains software and all of its dependencies. . For example, file system details, information about the container itself, and other cluster resources such as service endpoints.
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Container Lifecycle HooksLINK
The lifecycle hooks expose events in the ContainerA lightweight and portable executable image that contains software and all of its dependencies. management lifecycle and let the user run code when the events occur.
[+]Two hooks are exposed to Containers: PostStart which executes immediately after a container is created and PreStop which is blocking and is called immediately before a container is terminated.
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Container network interface (CNI)LINK
Container network interface (CNI) plugins are a type of Network plugin that adheres to the appc/CNI specification.
[+]- For information on Kubernetes and CNI refer to this.
- For information on Kubernetes and CNI, see “Network plugins”.
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Container RuntimeLINK
The container runtime is the software that is responsible for running containers.
[+]Kubernetes supports several container runtimes: Docker, containerd, cri-o, rktlet and any implementation of the Kubernetes CRI (Container Runtime Interface).
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Container Storage Interface (CSI)LINK
The Container Storage Interface (CSI) defines a standard interface to expose storage systems to containers.
[+]CSI allows vendors to create custom storage plugins for Kubernetes without adding them to the Kubernetes repository (out-of-tree plugins). To use a CSI driver from a storage provider, you must first deploy it to your cluster. You will then be able to create a Storage ClassA StorageClass provides a way for administrators to describe different available storage types. that uses that CSI driver.
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containerdLINK
A container runtime with an emphasis on simplicity, robustness and portability
[+]containerd is a containerA lightweight and portable executable image that contains software and all of its dependencies. runtime that runs as a daemon on Linux or Windows. containerd takes care of fetching and storing container images, executing containers, providing network access, and more.
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ContributorLINK
Someone who donates code, documentation, or their time to help the Kubernetes project or community.
[+]Contributions include pull requests (PRs), issues, feedback, special interest groups (SIG)Community members who collectively manage an ongoing piece or aspect of the larger Kubernetes open source project. participation, or organizing community events.
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ControllerLINK
In Kubernetes, controllers are control loops that watch the state of your clusterA set of machines, called nodes, that run containerized applications managed by Kubernetes. A cluster has at least one worker node and at least one master node. , then make or request changes where needed. Each controller tries to move the current cluster state closer to the desired state.
[+]Controllers watch the shared state of your cluster through the apiserverControl plane component that serves the Kubernetes API. (part of the Control PlaneThe container orchestration layer that exposes the API and interfaces to define, deploy, and manage the lifecycle of containers. ).
Some controllers also run inside the control plane, providing control loops that are core to Kubernetes’ operations. For example: the deployment controller, the daemonset controller, the namespace controller, and the persistent volume controller (and others) all run within the kube-controller-managerComponent on the master that runs controllers. .
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CRI-OLINK
A tool that lets you use OCI container runtimes with Kubernetes CRI.
[+]CRI-O is an implementation of the Container runtime interface (CRI)An API for container runtimes to integrate with kubelet to enable using containerA lightweight and portable executable image that contains software and all of its dependencies. runtimes that are compatible with the Open Container Initiative (OCI) runtime spec.
Deploying CRI-O allows Kubernetes to use any OCI-compliant runtime as the container runtime for running PodsThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. , and to fetch OCI container images from remote registries.
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DaemonSetLINK
Ensures a copy of a PodThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. is running across a set of nodes in a clusterA set of machines, called nodes, that run containerized applications managed by Kubernetes. A cluster has at least one worker node and at least one master node. .
[+]Used to deploy system daemons such as log collectors and monitoring agents that typically must run on every NodeA node is a worker machine in Kubernetes. .
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DeploymentLINK
An API object that manages a replicated application.
[+]Each replica is represented by a PodThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. , and the Pods are distributed among the nodes of a cluster.
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Developer (disambiguation)LINK
May refer to: Application DeveloperA person who writes an application that runs in a Kubernetes cluster. , Code ContributorA person who develops and contributes code to the Kubernetes open source codebase. , or Platform DeveloperA person who customizes the Kubernetes platform to fit the needs of their project. .
[+]This overloaded term may have different meanings depending on the context
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Device PluginLINK
Device Plugins are containers running in Kubernetes that provide access to a vendor specific resource.
[+]Device Plugins are containers running in Kubernetes that provide access to a vendor-specific resource. Device Plugins advertise these resources to KubeletAn agent that runs on each node in the cluster. It makes sure that containers are running in a pod. . They can be deployed manually or as a DaemonSetEnsures a copy of a Pod is running across a set of nodes in a cluster. , rather than writing custom Kubernetes code.
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DisruptionLINK
Disruptions are events that lead to one or more PodsThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. going out of service. A disruption has consequences for workload resources, such as DeploymentAn API object that manages a replicated application. , that rely on the affected Pods.
[+]If you, as cluster operator, destroy a Pod that belongs to an application, Kubernetes terms that a voluntary disruption. If a Pod goes offline because of a Node failure, or an outage affecting a wider failure zone, Kubernetes terms that an involuntary disruption.
See Disruptions for more information.
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DockerLINK
Docker (specifically, Docker Engine) is a software technology providing operating-system-level virtualization also known as containersA lightweight and portable executable image that contains software and all of its dependencies. .
[+]Docker uses the resource isolation features of the Linux kernel such as cgroups and kernel namespaces, and a union-capable file system such as OverlayFS and others to allow independent containers to run within a single Linux instance, avoiding the overhead of starting and maintaining virtual machines (VMs).
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Downstream (disambiguation)LINK
May refer to: code in the Kubernetes ecosystem that depends upon the core Kubernetes codebase or a forked repo.
[+]- In the Kubernetes Community: Conversations often use downstream to mean the ecosystem, code, or third-party tools that rely on the core Kubernetes codebase. For example, a new feature in Kubernetes may be adopted by applications downstream to improve their functionality.
- In GitHub or git: The convention is to refer to a forked repo as downstream, whereas the source repo is considered upstream.
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Dynamic Volume ProvisioningLINK
Allows users to request automatic creation of storage VolumesA directory containing data, accessible to the containers in a pod. .
[+]Dynamic provisioning eliminates the need for cluster administrators to pre-provision storage. Instead, it automatically provisions storage by user request. Dynamic volume provisioning is based on an API object, StorageClassA StorageClass provides a way for administrators to describe different available storage types. , referring to a Volume PluginA Volume Plugin enables integration of storage within a Pod. that provisions a VolumeA directory containing data, accessible to the containers in a pod. and the set of parameters to pass to the Volume Plugin.
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Endpoint SliceLINK
A way to group network endpoints together with Kubernetes resources.
[+]A scalable and extensible way to group network endpoints together. These can be used by kube-proxykube-proxy is a network proxy that runs on each node in the cluster. to establish network routes on each nodeA node is a worker machine in Kubernetes. .
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Ephemeral ContainerLINK
A ContainerA lightweight and portable executable image that contains software and all of its dependencies. type that you can temporarily run inside a PodThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. .
[+]If you want to investigate a Pod that’s running with problems, you can add an ephemeral container to that Pod and carry out diagnostics. Ephemeral containers have no resource or scheduling guarantees, and you should not use them to run any part of the workload itself.
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etcdLINK
Consistent and highly-available key value store used as Kubernetes’ backing store for all cluster data.
[+]If your Kubernetes cluster uses etcd as its backing store, make sure you have a back up plan for those data.
You can find in-depth information about etcd in the official documentation.
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ExtensionsLINK
Extensions are software components that extend and deeply integrate with Kubernetes to support new types of hardware.
[+]Most cluster administrators will use a hosted or distribution instance of Kubernetes. As a result, most Kubernetes users will need to install extensions and fewer will need to author new ones.
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FlexVolumeLINK
FlexVolume is an interface for creating out-of-tree volume plugins. The Container Storage InterfaceThe Container Storage Interface (CSI) defines a standard interface to expose storage systems to containers. is a newer interface which addresses several problems with FlexVolumes.
[+]FlexVolumes enable users to write their own drivers and add support for their volumes in Kubernetes. FlexVolume driver binaries and dependencies must be installed on host machines. This requires root access. The Storage SIG suggests implementing a CSIThe Container Storage Interface (CSI) defines a standard interface to expose storage systems to containers. driver if possible since it addresses the limitations with FlexVolumes.
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Helm ChartLINK
A package of pre-configured Kubernetes resources that can be managed with the Helm tool.
[+]Charts provide a reproducible way of creating and sharing Kubernetes applications. A single chart can be used to deploy something simple, like a memcached Pod, or something complex, like a full web app stack with HTTP servers, databases, caches, and so on.
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Horizontal Pod AutoscalerLINK
An API resource that automatically scales the number of pod replicas based on targeted CPU utilization or custom metric targets.
[+]HPA is typically used with Replication ControllersKubernetes service that ensures a specific number of instances of a pod are always running. , DeploymentsAn API object that manages a replicated application. , or Replica Sets. It cannot be applied to objects that cannot be scaled, for example DaemonSetsEnsures a copy of a Pod is running across a set of nodes in a cluster. .
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HostAliasesLINK
A HostAliases is a mapping between the IP address and hostname to be injected into a Pod’s hosts file.
[+]HostAliases is an optional list of hostnames and IP addresses that will be injected into the Pod’s hosts file if specified. This is only valid for non-hostNetwork Pods.
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ImageLINK
Stored instance of a container that holds a set of software needed to run an application.
[+]A way of packaging software that allows it to be stored in a container registry, pulled to a local system, and run as an application. Meta data is included in the image that can indicate what executable to run, who built it, and other information.
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Init ContainerLINK
One or more initialization containers that must run to completion before any app containers run.
[+]Initialization (init) containers are like regular app containers, with one difference: init containers must run to completion before any app containers can start. Init containers run in series: each init container must run to completion before the next init container begins.
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IstioLINK
An open platform (not Kubernetes-specific) that provides a uniform way to integrate microservices, manage traffic flow, enforce policies, and aggregate telemetry data.
[+]Adding Istio does not require changing application code. It is a layer of infrastructure between a service and the network, which when combined with service deployments, is commonly referred to as a service mesh. Istio’s control plane abstracts away the underlying cluster management platform, which may be Kubernetes, Mesosphere, etc.
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JobLINK
A finite or batch task that runs to completion.
[+]Creates one or more PodThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. objects and ensures that a specified number of them successfully terminate. As Pods successfully complete, the Job tracks the successful completions.
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KopsLINK
A CLI tool that helps you create, destroy, upgrade and maintain production-grade, highly available, Kubernetes clusters.
[+]Note: kops has general availability support only for AWS. Support for using kops with GCE and VMware vSphere are in alpha.kopsprovisions your cluster with:- Fully automated installation
- DNS-based cluster identification
- Self-healing: everything runs in Auto-Scaling Groups
- Limited OS support (Debian preferred, Ubuntu 16.04 supported, early support for CentOS & RHEL)
- High availability (HA) support
- The ability to directly provision, or to generate Terraform manifests
You can also build your own cluster using KubeadmA tool for quickly installing Kubernetes and setting up a secure cluster. as a building block.
kopsbuilds on the kubeadm work. -
kube-controller-managerLINK
Component on the master that runs controllersA control loop that watches the shared state of the cluster through the apiserver and makes changes attempting to move the current state towards the desired state. .
[+]Logically, each controllerA control loop that watches the shared state of the cluster through the apiserver and makes changes attempting to move the current state towards the desired state. is a separate process, but to reduce complexity, they are all compiled into a single binary and run in a single process.
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kube-proxyLINK
kube-proxy is a network proxy that runs on each node in your cluster, implementing part of the Kubernetes ServiceA way to expose an application running on a set of Pods as a network service. concept.
[+]kube-proxy maintains network rules on nodes. These network rules allow network communication to your Pods from network sessions inside or outside of your cluster.
kube-proxy uses the operating system packet filtering layer if there is one and it’s available. Otherwise, kube-proxy forwards the traffic itself.
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kube-schedulerLINK
Component on the master that watches newly created pods that have no node assigned, and selects a node for them to run on.
[+]Factors taken into account for scheduling decisions include individual and collective resource requirements, hardware/software/policy constraints, affinity and anti-affinity specifications, data locality, inter-workload interference and deadlines.
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KubectlLINK
A command line tool for communicating with a Kubernetes APIThe application that serves Kubernetes functionality through a RESTful interface and stores the state of the cluster. server.
[+]You can use kubectl to create, inspect, update, and delete Kubernetes objects.
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KubeletLINK
An agent that runs on each node in the cluster. It makes sure that containers are running in a pod.
[+]The kubelet takes a set of PodSpecs that are provided through various mechanisms and ensures that the containers described in those PodSpecs are running and healthy. The kubelet doesn’t manage containers which were not created by Kubernetes.
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Kubernetes APILINK
The application that serves Kubernetes functionality through a RESTful interface and stores the state of the cluster.
[+]Kubernetes resources and “records of intent” are all stored as API objects, and modified via RESTful calls to the API. The API allows configuration to be managed in a declarative way. Users can interact with the Kubernetes API directly, or via tools like
kubectl. The core Kubernetes API is flexible and can also be extended to support custom resources. -
LabelLINK
Tags objects with identifying attributes that are meaningful and relevant to users.
[+]Labels are key/value pairs that are attached to objects such as PodsThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. . They are used to organize and to select subsets of objects.
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LimitRangeLINK
Provides constraints to limit resource consumption per ContainersA lightweight and portable executable image that contains software and all of its dependencies. or PodsThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. in a namespace.
[+]LimitRange limits the quantity of objects that can be created by type, as well as the amount of compute resources that may be requested/consumed by individual ContainersA lightweight and portable executable image that contains software and all of its dependencies. or PodsThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. in a namespace.
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LoggingLINK
Logs are the list of events that are logged by clusterA set of machines, called nodes, that run containerized applications managed by Kubernetes. A cluster has at least one worker node and at least one master node. or application.
[+]Application and systems logs can help you understand what is happening inside your cluster. The logs are particularly useful for debugging problems and monitoring cluster activity.
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Managed ServiceLINK
A software offering maintained by a third-party provider.
[+]Some examples of Managed Services are AWS EC2, Azure SQL Database, and GCP Pub/Sub, but they can be any software offering that can be used by an application. Service Catalog provides a way to list, provision, and bind with Managed Services offered by Service BrokersAn endpoint for a set of Managed Services offered and maintained by a third-party. .
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MemberLINK
A continuously active contributorSomeone who donates code, documentation, or their time to help the Kubernetes project or community. in the K8s community.
[+]Members can have issues and PRs assigned to them and participate in special interest groups (SIGs)Community members who collectively manage an ongoing piece or aspect of the larger Kubernetes open source project. through GitHub teams. Pre-submit tests are automatically run for members’ PRs. A member is expected to remain an active contributor to the community.
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MinikubeLINK
A tool for running Kubernetes locally.
[+]Minikube runs a single-node cluster inside a VM on your computer. You can use Minikube to try Kubernetes in a learning environment.
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Mirror PodLINK
A podThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. object that a kubelet uses to represent a static podA pod managed directly by the kubelet daemon on a specific node.
[+]When the kubelet finds a static pod in its configuration, it automatically tries to create a Pod object on the Kubernetes API server for it. This means that the pod will be visible on the API server, but cannot be controlled from there.
(For example, removing a mirror pod will not stop the kubelet daemon from running it).
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NamespaceLINK
An abstraction used by Kubernetes to support multiple virtual clusters on the same physical clusterA set of machines, called nodes, that run containerized applications managed by Kubernetes. A cluster has at least one worker node and at least one master node. .
[+]Namespaces are used to organize objects in a cluster and provide a way to divide cluster resources. Names of resources need to be unique within a namespace, but not across namespaces.
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Network PolicyLINK
A specification of how groups of Pods are allowed to communicate with each other and with other network endpoints.
[+]Network Policies help you declaratively configure which Pods are allowed to connect to each other, which namespaces are allowed to communicate, and more specifically which port numbers to enforce each policy on.
NetworkPolicyresources use labels to select Pods and define rules which specify what traffic is allowed to the selected Pods. Network Policies are implemented by a supported network plugin provided by a network provider. Be aware that creating a network resource without a controller to implement it will have no effect. -
NodeLINK
A node is a worker machine in Kubernetes.
[+]A worker node may be a VM or physical machine, depending on the cluster. It has local daemons or services necessary to run PodsThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. and is managed by the control plane. The daemons on a node include kubeletAn agent that runs on each node in the cluster. It makes sure that containers are running in a pod. , kube-proxykube-proxy is a network proxy that runs on each node in the cluster. , and a container runtime implementing the CRIAn API for container runtimes to integrate with kubelet such as DockerDocker is a software technology providing operating-system-level virtualization also known as containers. .
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Operator patternLINK
The operator pattern is a system design that links a ControllerA control loop that watches the shared state of the cluster through the apiserver and makes changes attempting to move the current state towards the desired state. to one or more custom resources.
[+]You can extend Kubernetes by adding controllers to your cluster, beyond the built-in controllers that come as part of Kubernetes itself.
If a running application acts as a controller and has API access to carry out tasks against a custom resource that’s defined in the control plane, that’s an example of the Operator pattern.
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Persistent VolumeLINK
An API object that represents a piece of storage in the cluster. Available as a general, pluggable resource that persists beyond the lifecycle of any individual PodThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. .
[+]PersistentVolumes (PVs) provide an API that abstracts details of how storage is provided from how it is consumed. PVs are used directly in scenarios where storage can be created ahead of time (static provisioning). For scenarios that require on-demand storage (dynamic provisioning), PersistentVolumeClaims (PVCs) are used instead.
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Persistent Volume ClaimLINK
Claims storage resources defined in a PersistentVolume so that it can be mounted as a volume in a container.
[+]Specifies the amount of storage, how the storage will be accessed (read-only, read-write and/or exclusive) and how it is reclaimed (retained, recycled or deleted). Details of the storage itself are in the PersistentVolume specification.
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Platform DeveloperLINK
A person who customizes the Kubernetes platform to fit the needs of their project.
[+]A platform developer may, for example, use Custom Resources or Extend the Kubernetes API with the aggregation layer to add functionality to their instance of Kubernetes, specifically for their application. Some Platform Developers are also contributorsSomeone who donates code, documentation, or their time to help the Kubernetes project or community. and develop extensions which are contributed to the Kubernetes community. Others develop closed-source commercial or site-specific extensions.
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PodLINK
The smallest and simplest Kubernetes object. A Pod represents a set of running containersA lightweight and portable executable image that contains software and all of its dependencies. on your cluster.
[+]A Pod is typically set up to run a single primary container. It can also run optional sidecar containers that add supplementary features like logging. Pods are commonly managed by a DeploymentAn API object that manages a replicated application. .
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Pod Disruption BudgetLINKAlso known as:PDB
A Pod Disruption Budget allows an application owner to create an object for a replicated application, that ensures a certain number or percentage of Pods with an assigned label will not be voluntarily evicted at any point in time. PDBs cannot prevent an involuntary disruption, but will count against the budget. [+]A Pod Disruption Budget allows an application owner to create an object for a replicated application, that ensures a certain number or percentage of Pods with an assigned label will not be voluntarily evicted at any point in time. PDBs cannot prevent an involuntary disruption, but will count against the budget.
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Pod LifecycleLINK
A high-level summary of what phase the Pod is in within its lifecyle.
[+]The Pod Lifecycle is a high level summary of where a Pod is in its lifecyle. A Pod’s
statusfield is a PodStatus object, which has aphasefield that displays one of the following phases: Running, Pending, Succeeded, Failed, Unknown, Completed, or CrashLoopBackOff. -
Pod PriorityLINK
Pod Priority indicates the importance of a Pod relative to other Pods.
[+]Pod Priority gives the ability to set scheduling priority of a Pod to be higher and lower than other Pods — an important feature for production clusters workload.
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Pod Security PolicyLINK
Enables fine-grained authorization of PodThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. creation and updates.
[+]A cluster-level resource that controls security sensitive aspects of the Pod specification. The
PodSecurityPolicyobjects define a set of conditions that a Pod must run with in order to be accepted into the system, as well as defaults for the related fields. Pod Security Policy control is implemented as an optional admission controller. -
PodPresetLINK
An API object that injects information such as secrets, volume mounts, and environment variables into pods at creation time.
[+]This object chooses the pods to inject information into using standard selectors. This allows the podspec definitions to be nonspecific, decoupling the podspec from environment specific configuration.
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ProxyLINK
In computing, a proxy is a server that acts as an intermediary for a remote service.
[+]A client interacts with the proxy; the proxy copies the client’s data to the actual server; the actual server replies to the proxy; the proxy sends the actual server’s reply to the client.
kube-proxy is a network proxy that runs on each node in your cluster, implementing part of the Kubernetes ServiceA way to expose an application running on a set of Pods as a network service. concept.
You can run kube-proxy as a plain userland proxy service. If your operating system supports it, you can instead run kube-proxy in a hybrid mode that achieves the same overall effect using less system resources.
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QoS ClassLINK
QoS Class (Quality of Service Class) provides a way for Kubernetes to classify Pods within the cluster into several classes and make decisions about scheduling and eviction.
[+]QoS Class of a Pod is set at creation time based on its compute resources requests and limits settings. QoS classes are used to make decisions about Pods scheduling and eviction. Kubernetes can assign one of the following QoS classes to a Pod:
Guaranteed,BurstableorBestEffort. -
QuantityLINK
A whole-number representation of small or large numbers using SI suffixes.
[+]Quantities are representations of small or large numbers using a compact, whole-number notation with SI suffixes. Fractional numbers are represented using milli units, while large numbers can be represented using kilo, mega, or giga units.
For instance, the number
1.5is represented as1500m, while the number1000can be represented as1k, and1000000as1M. You can also specify binary-notation suffixes; the number 2048 can be written as2Ki.The accepted decimal (power-of-10) units are
m(milli),k(kilo, intentionally lowercase),M(mega),G(giga),T(terra),P(peta),E(exa).The accepted binary (power-of-2) units are
Ki(kibi),Mi(mebi),Gi(gibi),Ti(tebi),Pi(pebi),Ei(exbi). -
RBAC (Role-Based Access Control)LINK
Manages authorization decisions, allowing admins to dynamically configure access policies through the Kubernetes APIThe application that serves Kubernetes functionality through a RESTful interface and stores the state of the cluster. .
[+]RBAC utilizes roles, which contain permission rules, and role bindings, which grant the permissions defined in a role to a set of users.
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ReplicaSetLINK
A ReplicaSet (aims to) maintain a set of replica Pods running at any given time.
[+]Workload objects such as DeploymentAn API object that manages a replicated application. make use of ReplicaSets to ensure that the configured number of PodsThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. are running in your cluster, based on the spec of that ReplicaSet.
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Replication ControllerLINK
Kubernetes service that ensures a specific number of instances of a pod are always running.
[+]Will automatically add or remove running instances of a pod, based on a set value for that pod. Allows the pod to return to the defined number of instances if pods are deleted or if too many are started by mistake.
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Resource QuotasLINK
Provides constraints that limit aggregate resource consumption per NamespaceAn abstraction used by Kubernetes to support multiple virtual clusters on the same physical cluster. .
[+]Limits the quantity of objects that can be created in a namespace by type, as well as the total amount of compute resources that may be consumed by resources in that project.
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rktLINK
A security-minded, standards-based container engine.
[+]rkt is an application containerA lightweight and portable executable image that contains software and all of its dependencies. engine featuring a PodThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. -native approach, a pluggable execution environment, and a well-defined surface area. rkt allows users to apply different configurations at both the Pod and application level. Each Pod executes directly in the classic Unix process model, in a self-contained, isolated environment.
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SecretLINK
Stores sensitive information, such as passwords, OAuth tokens, and ssh keys.
[+]Allows for more control over how sensitive information is used and reduces the risk of accidental exposure, including encryption at rest. A PodThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. references the secret as a file in a volume mount or by the kubelet pulling images for a pod. Secrets are great for confidential data and ConfigMaps for non-confidential data.
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Security ContextLINK
The securityContext field defines privilege and access control settings for a Pod or Container, including the runtime UID and GID.
[+]The securityContext field in a PodThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. (applying to all containers) or container is used to set the user, groups, capabilities, privilege settings, and security policies (SELinux/AppArmor/Seccomp) and more that container processes use.
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SelectorLINK
Allows users to filter a list of resources based on labels.
[+]Selectors are applied when querying lists of resources to filter them by LabelsTags objects with identifying attributes that are meaningful and relevant to users. .
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ServiceLINK
An abstract way to expose an application running on a set of PodsThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. as a network service.
[+]The set of Pods targeted by a Service is (usually) determined by a selectorAllows users to filter a list of resources based on labels. . If more Pods are added or removed, the set of Pods matching the selector will change. The Service makes sure that network traffic can be directed to the current set of Pods for the workload.
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Service AccountLINK
Provides an identity for processes that run in a PodThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. .
[+]When processes inside Pods access the cluster, they are authenticated by the API server as a particular service account, for example,
default. When you create a Pod, if you do not specify a service account, it is automatically assigned the default service account in the same namespace NamespaceAn abstraction used by Kubernetes to support multiple virtual clusters on the same physical cluster. . -
Service BrokerLINK
An endpoint for a set of Managed ServicesA software offering maintained by a third-party provider. offered and maintained by a third-party.
[+]Service BrokersAn endpoint for a set of Managed Services offered and maintained by a third-party. implement the Open Service Broker API spec and provide a standard interface for applications to use their Managed Services. Service Catalog provides a way to list, provision, and bind with Managed Services offered by Service Brokers.
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Service CatalogLINK
An extension API that enables applications running in Kubernetes clusters to easily use external managed software offerings, such as a datastore service offered by a cloud provider.
[+]It provides a way to list, provision, and bind with external Managed ServicesA software offering maintained by a third-party provider. from Service BrokersAn endpoint for a set of Managed Services offered and maintained by a third-party. without needing detailed knowledge about how those services are created or managed.
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SIG (special interest group)LINK
Community membersA continuously active contributor in the K8s community. who collectively manage an ongoing piece or aspect of the larger Kubernetes open source project.
[+]Members within a SIG have a shared interest in advancing a specific area, such as architecture, API machinery, or documentation. SIGs must follow the SIG governance guidelines, but can have their own contribution policy and channels of communication.
For more information, see the kubernetes/community repo and the current list of SIGs and Working Groups.
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StatefulSetLINK
Manages the deployment and scaling of a set of PodsThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. , and provides guarantees about the ordering and uniqueness of these Pods.
[+]Like a DeploymentAn API object that manages a replicated application. , a StatefulSet manages Pods that are based on an identical container spec. Unlike a Deployment, a StatefulSet maintains a sticky identity for each of their Pods. These pods are created from the same spec, but are not interchangeable: each has a persistent identifier that it maintains across any rescheduling.
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Static PodLINK
A podThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. managed directly by the kubelet daemon on a specific node,
[+]without the API server observing it.
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Storage ClassLINK
A StorageClass provides a way for administrators to describe different available storage types.
[+]StorageClasses can map to quality-of-service levels, backup policies, or to arbitrary policies determined by cluster administrators. Each StorageClass contains the fields
provisioner,parameters, andreclaimPolicy, which are used when a Persistent VolumeAn API object that represents a piece of storage in the cluster. Available as a general, pluggable resource that persists beyond the lifecycle of any individual Pod. belonging to the class needs to be dynamically provisioned. Users can request a particular class using the name of a StorageClass object. -
sysctlLINK
[+]sysctlis a semi-standardized interface for reading or changing the attributes of the running Unix kernel.On Unix-like systems,
sysctlis both the name of the tool that administrators use to view and modify these settings, and also the system call that the tool uses.ContainerA lightweight and portable executable image that contains software and all of its dependencies. runtimes and network plugins may rely on
sysctlvalues being set a certain way. -
TaintLINK
A core object consisting of three required properties: key, value, and effect. Taints prevent the scheduling of pods on nodes or node groups.
[+]Taints and tolerationsA core object consisting of three required properties: key, value, and effect. Tolerations enable the scheduling of pods on nodes or node groups that have a matching taint. work together to ensure that pods are not scheduled onto inappropriate nodes. One or more taints are applied to a nodeA node is a worker machine in Kubernetes. . A node should only schedule a pod with the matching tolerations for the configured taints.
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TolerationLINK
A core object consisting of three required properties: key, value, and effect. Tolerations enable the scheduling of pods on nodes or node groups that have matching taintsA core object consisting of three required properties: key, value, and effect. Taints prevent the scheduling of pods on nodes or node groups. .
[+]Tolerations and taintsA core object consisting of three required properties: key, value, and effect. Taints prevent the scheduling of pods on nodes or node groups. work together to ensure that pods are not scheduled onto inappropriate nodes. One or more tolerations are applied to a podThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. . A toleration indicates that the podThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. is allowed (but not required) to be scheduled on nodes or node groups with matching taintsA core object consisting of three required properties: key, value, and effect. Taints prevent the scheduling of pods on nodes or node groups. .
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Upstream (disambiguation)LINK
May refer to: core Kubernetes or the source repo from which a repo was forked.
[+]- In the Kubernetes Community: Conversations often use upstream to mean the core Kubernetes codebase, which the general ecosystem, other code, or third-party tools relies upon. For example, community members may suggest that a feature is moved upstream so that it is in the core codebase instead of in a plugin or third-party tool.
- In GitHub or git: The convention is to refer to a source repo as upstream, whereas the forked repo is considered downstream.
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VolumeLINK
A directory containing data, accessible to the containers in a podThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. .
[+]A Kubernetes volume lives as long as the podThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. that encloses it. Consequently, a volume outlives any containersA lightweight and portable executable image that contains software and all of its dependencies. that run within the podThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. , and data is preserved across containerA lightweight and portable executable image that contains software and all of its dependencies. restarts.
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Volume PluginLINK
A Volume Plugin enables integration of storage within a PodThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. .
[+]A Volume Plugin lets you attach and mount storage volumes for use by a PodThe smallest and simplest Kubernetes object. A Pod represents a set of running containers on your cluster. . Volume plugins can be in tree or out of tree. In tree plugins are part of the Kubernetes code repository and follow its release cycle. Out of tree plugins are developed independently.
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WG (working group)LINK
Facilitates the discussion and/or implementation of a short-lived, narrow, or decoupled project for a committee, SIGCommunity members who collectively manage an ongoing piece or aspect of the larger Kubernetes open source project. , or cross-SIG effort.
[+]Working groups are a way of organizing people to accomplish a discrete task, and are relatively easy to create and deprecate when inactive.
For more information, see the kubernetes/community repo and the current list of SIGs and working groups.
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WorkloadLINK
A workload is an application running on Kubernetes.
[+]Various core objects that represent different types or parts of a workload include the DaemonSet, Deployment, Job, ReplicaSet, and StatefulSet objects.
For example, a workload that has a web server and a database might run the database in one StatefulSetManages the deployment and scaling of a set of Pods, and provides guarantees about the ordering and uniqueness of these Pods. and the web server in a DeploymentAn API object that manages a replicated application. .
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