Networking

A Docker network is the system that lets containers communicate with each other and with the outside world. Docker creates isolated virtual networks and connects containers to them, controlling what can talk to what.

⚠️ The default bridge network (the one that exists without creating anything) does NOT have internal DNS between containers — only bridge networks created explicitly with docker network create do. It’s the most common trap: two containers on the default network don’t resolve each other by name.

Example

In practice you almost always use a bridge network you create yourself — which is exactly what Docker Compose sets up under the hood without you noticing.

docker network create my-net

docker run -d --name db  --network my-net postgres:16
docker run -d --name app --network my-net -p 8080:3000 my-app:1.0   # your image

All containers on my-net see each other by name (DNS): inside app you connect to the database with db:5432, without knowing its IP. Only what you publish with -p is exposed to the outside.

Other drivers exist for specific cases — host (shares the host’s network, no isolation), none (no network) and overlay (multiple machines, the basis of Docker Swarm) — but day to day, and especially with Compose, you work with bridge.

Inspect and clean up

docker network ls              # list networks
docker network inspect my-net  # see which containers are connected
docker network rm my-net       # remove it (must have no containers)