How to debug persistent data volume mount for Docker Odoo container? - docker

Question

I followed the standard Odoo container instructions on Docker to start the required postgres and odoo servers, and tried to pass host directories as persistent data storage for both as indicated in those instructions:
sudo mkdir /tmp/postgres /tmp/odoo
sudo docker run -d -v /tmp/postgres:/var/lib/postgresql/data/pgdata -e POSTGRES_USER=odoo -e POSTGRES_PASSWORD=odoo -e POSTGRES_DB=postgres --name db postgres:10
sudo docker run -v /tmp/odoo:/var/lib/odoo -p 8069:8069 --name odoo --link db:db -t odoo
The Odoo container shows messages that it starts up fine, but when I point my web browser at http://localhost:8069 I get no response from the server. By contrast, if I omit the -v argument from the Odoo docker run command, my web browser connects to the Odoo server fine, and everything works great.
I searched and see other people also struggling with getting the details of persistent data volumes working, e.g. Odoo development on Docker, Encountered errors while bringing up the project
This seems like a significant gap in Docker's standard use-case that users need better info on how to debug:
How to debug why the host volume mounting doesn't work for the odoo container, whereas it clearly does work for the postgres container? I'm not getting any insight from the log messages.
In particular, how to debug whether the container requires the host data volume to be pre-configured in some specific way, in order to work? For example, the fact that I can get the container to work without the -v option seems like it ought to be helpful, but also rather opaque. How can I use that success to inspect what those requirements actually are?
Docker is supposed to help you get a useful service running without needing to know the guts of its internals, e.g. how to set up its internal data directory. Mounting a persistent data volume from the host is a key part of that, e.g. so that users can snapshot, backup and restore their data using tools they already know.

Answer 1

I figured out some good debugging methods that both solved this problem and seem generally useful for figuring out Docker persistent data volume issues.
Test 1: can the container work with an empty Docker volume?
This is a really easy test: just create a new Docker volume and pass that in your -v argument (instead of a host directory absolute path):
sudo docker volume create hello
sudo docker run -v hello:/var/lib/odoo -p 8069:8069 --name odoo --link db:db -t odoo
The odoo container immediately worked successfully this way (i.e. my web browswer was able to connect to the Odoo server). This showed that it could work fine with an (initially) empty data directory. The obvious question then is why it didn't work with an empty host-directory volume. I had read that Docker containers can be persnickety about UID/GID ownership, so my next question was how do I figure out what it expects.
Test 2: inspect the running container's file system
I used docker exec to get an interactive bash shell in the running container:
sudo docker exec -ti odoo bash
Inside this shell I then looked at the data directory ownership, to get numeric UID and GID values:
ls -dn /var/lib/odoo
This showed me the UID/GID values were 101:101. (You can exit from this shell by just typing Control-D)
Test 3: re-run container with matching host-directory UID:GID
I then changed the ownership of my host directory to 101:101 and re-ran the odoo container with my host-directory mount:
sudo chown 101:101 /tmp/odoo
sudo docker stop odoo
sudo docker rm odoo
sudo docker run -v /tmp/odoo:/var/lib/odoo -p 8069:8069 --name odoo --link db:db -t odoo
Success! Finally the odoo container worked properly with a host-directory mount. While it's annoying the Odoo docker docs don't mention anything about this, it's easy to debug if you know how to use these basic tests.