I'm running Docker on a Debian VM through Proxmox and I've set up a NAS for storage, which I mount using fstab. Everything's worked smoothly until now. My concern is how to handle scenarios where the NAS goes offline—like during a reboot or if the network switch fails. Is there a way to configure my Docker setup so that containers don't start unless the NAS storage is available? Also, if the connection drops while a container is running, I'd like it to shut down immediately. What's the best approach to achieve this?
5 Answers
Consider defining the volume in your compose.yml instead of mounting it on the host. This way, if the mount fails, the container won't even start, which could be a safety net for you.
That makes sense for portability! Do you have a link to an example? Most guides I've followed showed mounts at the host level.
You could use a hook script to prevent the VM from booting if the storage isn't there. I have one that checks for a specific file in the mounted directory; if it's missing, the VM won't start. Here’s a sample script I wrote:
```
#! /bin/bash
VMID="$1"
PHASE="$2"
MOUNT_BASE="/mnt/pve/docker-cephFS"
MARKER_FILE=".donotdelete"
MARKER_PATH="${MOUNT_BASE}/${MARKER_FILE}"
if [[ "$PHASE" == "pre-start" && ! -e "$MARKER_PATH" ]]; then
echo "VM $VMID start blocked: ${MARKER_PATH} missing."
exit 1
fi
```
You could modify this to also check on shutdown by implementing additional phases in the script.
That sounds smart! Adding checks for other phases like running or shutdown would really make your script robust.
Have you checked out Docker Compose's health check feature? It allows you to define health checks for your containers. If the NAS fails and the check fails, Docker won't run the container, which could be handy for your situation.
Why not just use NFS for your mounts? It should simplify the process. You wouldn't have to deal with local storage issues; you'd mount directly on the NAS.
I thought that would create a new storage volume on the NAS rather than mount an existing one. I didn’t dig into it too deep since fstab was straightforward and worked well.
You might want to look into using the 'chattr +i' command on your mount point. This makes the mount immutable so that if it disappears, it might prevent your containers from messing with local storage instead of the NAS. But just to confirm, when the NAS goes down, will you still get read-only errors in your container since it's trying to write to your Debian storage?
Yes, if the NAS is down and the local storage is writable, your containers might start writing there instead. Using chattr can help ensure they don't accidentally store data locally, which is really what you want.
Would that cause the container to crash if the mount disconnects later? I’m just getting into Docker, so I'm curious.