The docker container updating service Ouroboros works well on a Synology NAS. How ever one can’t create the container through the DSM GUI because it needs a special volume mount (/var/run/docker.sock).

To create the container through a terminal and start it the first time, run

sudo docker run -d --name ouroboros -e INTERVAL=45000 -e LOGLEVEL=info -e SELF_UPDATE=true -e RUNONCE=false -e CLEANUP=true -e TZ=Europe/Zurich -v /var/run/docker.sock:/var/run/docker.sock --restart unless-stopped pyouroboros/ouroboros

Compared to Watchtower it supports more configuration and is actively maintained.

Example by appending the parameter -n 'tgram://1234:DEADBEEF/1234567/' it sends you automatically a telegram if a container got updated.