How to Ensure Stable Docker Container Communication Without Relying on Changing IPs

1. Connecting via IP

Containers have a virtual bridge and can be assigned their own IP addresses, allowing direct IP‑based communication. After launching two containers and checking their IPs (e.g., 192.168.42.4 and 192.168.42.5), a ping from one to the other succeeds, confirming network connectivity.

However, container IPs change after a restart, making IP‑based communication unreliable.

2. Connecting via container name

Docker provides an alias linking mechanism that removes the dependency on IP addresses. First, start a container with a name: docker run -d -p 22 --name net001 dys/centos:ssh The --name net001 option assigns the name net001 to the container, which persists across Docker service restarts.

Start a second container and link it to the first one:

docker run -d -p 22 --name net002 --link net001:lk001 dys/centos:ssh

The --link net001:lk001 option creates an alias lk001 for net001. Inside net002, you can ping net001 (or lk001) and the connection succeeds, regardless of the first container’s IP changes.

What Docker does

Docker updates the /etc/hosts file inside the linked container. For example, after linking, cat /etc/hosts in net002 shows a line such as: 192.168.42.4 lk001 4193f1ac3f78 net001 When net001 receives a new IP after a restart, Docker automatically rewrites this entry, ensuring that name‑based communication remains stable.