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Docker Volumes and Networks

Keep data after a container is removed, and let containers talk to each other by name.

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  • Docker Engine 19.03.12
  • PostgreSQL 12

Volumes hold data outside the container’s writable layer.

docker volume create pgdata
docker run -d --name db -v pgdata:/var/lib/postgresql/data \
  -e POSTGRES_PASSWORD=change-me postgres:12
docker rm -f db
docker run -d --name db -v pgdata:/var/lib/postgresql/data \
  -e POSTGRES_PASSWORD=change-me postgres:12      # data is still there

A bind mount (-v /host/path:/container/path) maps a host directory and suits development. For production data prefer named volumes.

On a user-defined network, containers resolve each other by name:

docker network create appnet
docker run -d --name db --network appnet postgres:12
docker run -it --rm --network appnet postgres:12 psql -h db -U postgres

The default bridge network has no name-based discovery, so always create your own. Publish only the ports that outside clients need; containers on the same network reach each other without -p.