Many cloud providers (e.g. Google Compute Engine) define firewalls that help keep 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.
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 There is one important security note when using firewalls on Google Compute Engine:
Firewalls are defined per-vm, rather than per-ip address. This means that if you open a firewall for that 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 Container Engine. You may accidentally be exposing other services to the wilds of the internet.
Coming soon.