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.
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
When using a Service with
spec.type: LoadBalancer, you can specify the IP ranges that are allowed to access the load balancer
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 126.96.36.199 and 188.8.131.52.
apiVersion: v1 kind: Service metadata: name: myapp spec: ports: - port: 8765 targetPort: 9376 selector: app: example type: LoadBalancer loadBalancerSourceRanges: - 184.108.40.206/32 - 220.127.116.11/32
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>
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.
- You create a Service with an external load balancer (IP Address 18.104.22.168) 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 22.214.171.124). 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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