Docker volumes
How you ever wondered how docker volumes work? Let’s jump into it real quick.
Mechanics behind docker volumes
- A special type of storage in docker.
- Designed to persist data independent of the container lifecycle.
- The idea is that when a container stops, crashes, or is deleted, the data stored in the volume remains intact as long as the volume itself is not deleted.
- Gives you data isolation.
- Bind mount:
- Directly maps a host (your local system filesystem) directory, into a docker volume.
- Volume:
- Is managed by docker and stored in docker’s storage directory (e.g.,
/var/lib/docker/volumes
on Linux).
- Is managed by docker and stored in docker’s storage directory (e.g.,
Compose files
-
E.g. in this compose file we Map a named volume (i.e.
postgres
) to the container path/var/lib/postgresql/data/pgdata
.That is where PostgreSQL stores its data files by default (ref). This ensures PostgreSQL’s database files are written to the volume.
-
To test it:
- Run this python script.
docker compose down
. Do NOT pass-v
flag since it will delete the volume along side the data.docker compose up -d
.- Check your database to see if everything is there.