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Configure Your Cloud Provider's Firewalls

Many cloud providers (e.g. Google Compute Engine) define firewalls that help prevent inadvertent exposure to the internet. When exposing a service to the external world, you may need to open up one or more ports in these firewalls to serve traffic. This document describes this process, as well as any provider specific details that may be necessary.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using Minikube, or you can use one of these Kubernetes playgrounds:

To check the version, enter kubectl version.

Restrict Access For LoadBalancer Service

When using a Service with spec.type: LoadBalancer, you can specify the IP ranges that are allowed to access the load balancer by using spec.loadBalancerSourceRanges. This field takes a list of IP CIDR ranges, which Kubernetes will use to configure firewall exceptions. This feature is currently supported on Google Compute Engine, Google Kubernetes Engine, AWS Elastic Kubernetes Service, Azure Kubernetes Service, and IBM Cloud Kubernetes Service. This field will be ignored if the cloud provider does not support the feature.

Assuming 10.0.0.0/8 is the internal subnet. In the following example, a load balancer will be created that is only accessible to cluster internal IPs. This will not allow clients from outside of your Kubernetes cluster to access the load balancer.

apiVersion: v1
kind: Service
metadata:
  name: myapp
spec:
  ports:
  - port: 8765
    targetPort: 9376
  selector:
    app: example
  type: LoadBalancer
  loadBalancerSourceRanges:
  - 10.0.0.0/8

In the following example, a load balancer will be created that is only accessible to clients with IP addresses from 130.211.204.1 and 130.211.204.2.

apiVersion: v1
kind: Service
metadata:
  name: myapp
spec:
  ports:
  - port: 8765
    targetPort: 9376
  selector:
    app: example
  type: LoadBalancer
  loadBalancerSourceRanges:
  - 130.211.204.1/32
  - 130.211.204.2/32

Google Compute Engine

When using a Service with spec.type: LoadBalancer, the firewall will be opened automatically. When using spec.type: NodePort, however, the firewall is not opened by default.

Google Compute Engine firewalls are documented elsewhere.

You can add a firewall with the gcloud command line tool:

gcloud compute firewall-rules create my-rule --allow=tcp:<port>
Note:

GCE firewalls are defined per-vm, rather than per-ip address. This means that when you open a firewall for a service’s ports, anything that serves on that port on that VM’s host IP address may potentially serve traffic. Note that this is not a problem for other Kubernetes services, as they listen on IP addresses that are different than the host node’s external IP address.

Consider:

  • You create a Service with an external load balancer (IP Address 1.2.3.4) and port 80
  • You open the firewall for port 80 for all nodes in your cluster, so that the external Service actually can deliver packets to your Service
  • You start an nginx server, running on port 80 on the host virtual machine (IP Address 2.3.4.5). This nginx is also exposed to the internet on the VM’s external IP address.

Consequently, please be careful when opening firewalls in Google Compute Engine or Google Kubernetes Engine. You may accidentally be exposing other services to the wilds of the internet.

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