Postal installed in LXD/LXC container.... docker container "lost" after copying the LXD container from server to laptop.

[JohnHammell]

My first Postal install, which was fairly recent, runs inside an LXD container. Everything seems to be running just right. I never have problems with restarting the LXD container as whenever I do Postal is right back up and running exactly as before the restart.

I'm running into a problem with copying the LXD container from my server to my laptop so I can do some local work on it, basically poke around a bit, etc, on a dev copy of the LXD container with Postal.

However, after I copy the LXD container with Postal none of docker containers are running. They all fail to start back up. Doing this same thing on my server to the original LXD container, restarting it, does not cause the Postal docker containers to stop running.

I've been able to get the web ui, smtp & worker postal docker containers back up pretty easily, just by running: postal start

The postal-mariadb container, though, kinda looks as though it's "lost." The folder for postal-mariadb is in /var/lib/docker, but when I try to start it I get a message that it is not found:

root@lxd-container-name:~# docker start postal-mariadb
Error response from daemon: No such container: postal-mariadb
Error: failed to start containers: postal-mariadb

Any idea what is going on with this?

Literally, all I did was stopped the LXD container with the actively running Postal installation, took an LXD snapshot of the container (which is basically as ZFS snapshot as far as I know), then downloaded that snapshot to my laptop. Then I start that LXD container on my laptop and the issues I described arise. Not really sure why Postal does not start back up on its own but the main issue is the "lost" postal-mariadb docker container.

"lost" is in quotes because I really don't know. Maybe I'm doing something wrong here or maybe there's some command I'm not aware of which needs to be used to get postal-mariadb started up again.

[willpower232]

I don't really know much about LXD but I do know that maria and mysql can be a bit funky with copying data around depending on the table type.

I'm also presuming you are running it with a data volume to preserve its contents so it might be worth stopping the container before the snapshot, to ensure the data is definitely stored locally. If that doesn't work, presumably you could mysqldump it.

[willpower232]

Ah interesting, it doesn't mention using a volume so I'm going to say that the docker container doesn't keep its data.

If it says no such container, what docker containers does the restored LXD container list?

[JohnHammell]

The postal containers (smtp, web & worker) seem to function normally when the LXD container is copied to my laptop from the server, but the postal-mariadb container does not & ends up "missing."

Initially none are listed with 'docker ps -a' but 'postal start' gets the postal containers going, other than postal-mariadb container.

Haven't figured out why yet. The postal-mariadb docker container works just fine and doesn't lose anything when I start/stop & restart the container on the server. I'll be moving that installation over to a non-docker install of mariadb soon, though, just to ensure I can get a container backup running again if I ever need to.

[willpower232]

Initially none are listed with 'docker ps -a'

Aha well there you go, taking a snapshot of the container does not capture any running containers, not just the database. Its just more annoying with the database as that needs a manual start unless you add it to Postals docker-compose.yml (although you probably want to backup the database more directly before you mess around with it too much as there isn't a volume as previously mentioned)

[JohnHammell]

The strange part is that LXD/LXC uses ZFS snapshots (when ZFS is the filesystem as I have) and ZFS snapshots do not discriminate data. ZFS snapshots are simply a 100% snapshot of data at that specific point in time. I suppose it would be similar to making an image copy of a hard drive. After taking the lxc snapshot it can be seen in zfs list to view zfs snapshots.

I'm pretty sure I tried doing this taking the snapshot while the container is both offline & online with the same result. I'll test again, though. I'll post an update after doing that.

[JohnHammell]

Tested again. 2 snapshots, one with the lxd/lxc container vm turned off and the other with it running. Both had the same result:

"postal status" returned no containers running.

"postal start" re-downloads/pulls the postal containers and gets them going again.

"docker start postal-mariadb" returns "Error response from daemon: No such container: postal-mariadb"