Problem
Some of my docker containers access resources from a NAS over NFS.
On reboot, the Docker service comes up before the NFS paths are mounted, this causes the services within my containers to fail.
Restating the docker service, systemctl restart docker fixes this but I’d rather the containers come up properly the first time.
Solution
Add a systemd drop-in unit for the docker service instructing it to wait for the NFS mount to come online before starting.
Steps
Identify the systemd unit for the NFS mount. In my case /nas/data .
danesh@antman:~$ mount -t nfs4
192.168.100.1:/volume8/data on /nas/data type nfs4 (rw,relatime,vers=4.1,rsize=131072,wsize=131072,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,clientaddr=192.168.100.2,local_lock=none,addr=192.168.100.1,_netdev)
danesh@antman:~$ sudo systemctl list-units | grep nas-data
nas-data.mount loaded active mounted /nas/data
Create the systemd drop-in unit file for the docker service. Create the directory if it is not there.
danesh@antman:~$ sudo mkdir /etc/systemd/system/docker.service.d/
danesh@antman:~$ sudo echo "[Unit]
After=nas-data.mount
Wants=nas-data.mount" >> /etc/systemd/system/docker.service.d/wait-for-nfs.conf
danesh@antman:~$ sudo cat /etc/systemd/system/docker.service.d/wait-for-nfs.conf
[sudo] password for danesh:
[Unit]
After=nas-data.mount
Wants=nas-data.mount
After: Start after NFS /nas/data is mounted.
Wants: If not already mounted, go ahead and mount /nas/data
If Wants is changed to Requires, the docker service will not start unless /nas/data is mounted.
Restart the docker service to verify that the drop-in is picked up.
danesh@antman:~$ sudo systemctl restart docker
danesh@antman:~$ sudo systemctl status docker
? docker.service - Docker Application Container Engine
Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
Drop-In: /etc/systemd/system/docker.service.d
??wait-for-nfs.conf
Active: active (running) since Mon 2020-08-31 20:45:40 UTC; 5h 21min ago
TriggeredBy: ? docker.socket
If the drop-in is showing then the change will now be persistent across reboots.