Yes. A volume attached to your Postgres service keeps its data between deployments, and your app service runs as its own separate container, so redeploying it does not redeploy or touch the Postgres service or its volume. The data persists because of the volume, so it only applies while one is attached to the Postgres service, mounted at /var/lib/postgresql/data for the Postgres image. Without a volume, the database would write to the container's temporary storage, which is wiped whenever the Postgres service itself redeploys. More detail is in our database and volume docs.