when running docker-compose, all containers have network aliases to the ip of the other containers running in the network. How are these aliases created ?
I need to recreate an alias in an nginx container within a Kubernetes cluster, because nginx conf doesn't allow environment variables and I reverse proxy requests to another container from there. I would normally edit the /etc/hosts file, but since docker-compose doesn't, I'm wondering how is the alias created and if I could do it the same way within my kubernetes cluster.
As written in the documentation
Containers for the linked service are reachable at a hostname identical to the alias, or the service name if no alias was specified
This means if you have a docker-compose file like this:
version: '3'
services:
nginx:
links:
- app1
...
app1:
...
Then nginx is able to access the other container by app1.
In a kubernetes cluster, there is a DNS server service deployed by default.
kubectl get svc should show the DNS service IP address.
You can find the DNS server IP address inside the containers /etc/resolv.conf file too.
See here for more info.
You can specify additional entries in container's /etc/hosts file using HostAliases. See here.
Snip:
apiVersion: v1
kind: Pod
metadata:
name: hostaliases-pod
spec:
restartPolicy: Never
hostAliases:
- ip: "127.0.0.1"
hostnames:
- "foo.local"
- "bar.local"
- ip: "10.1.2.3"
hostnames:
- "foo.remote"
- "bar.remote"