Bug with plugin when mapping docker volume on external drive for /var/lib/grafana

[jenshenk]

I ran into an interesting but confusing issue, most likely not uniquely connected to mqtt-datasource but to plugins in general

I'm using grafana 10.0.1 on a raspberry pi with docker and wanted the docker db reside on an external drive, Here's what's happening:

• created a volume on the external drive
• mapped that volume to /var/lib/grafana when starting docker
• grafana uses that volume and is able to install the mqtt plugin
• on trying to use the mqtt plugin I get the "plugin unavailable error.

Interestingly, when I map a docker volume that's on the SD card Docker and RaspiOS is running from the plugin gets installed and can be used without issues.

In another attempt I did the following, which might lead to fixing this bug

• Created a docker volume for /var/lib/grafana
• Created another docker volume for /var/lib/grafana/plugin
• Mapped both volumes to being used as data and plugins directory respectively
• Grafana is using the mapped volume /var/lib/grafana, HOWEVER the directory of the mapped volume for /var/lib/grafana/plugins remains empty
• Yet, grafana is able to install the plugin and use it without issues

Troubleshooting a bit more I found out that if I stop the container and unmount the external drive, the _data directory of the the mapped docker volume for /var/lib/grafana is empty, what makes sense. Where it becomes really interesting is that in the volumes directory from docker I now see a directory called grafanadataplugins that somehow was created by grafana and that remains having files when the external drive is unmounted. The plugins volume I specifically created and mapped for the plugins directory however was called grafanaplugins without the "data" in the name and that one is not being used.

I think the bug somehow revolves around the plugins directory being a subdirectory of the /var/lib/grafana directory and hope the above info helps to fix this issue.