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Watchtower — Automated Docker Updates on a Synology NAS

Last updated on 23 November 2023

Please note if you are using DSM7.2 or higher you should use the Container Manager version of this guide from the menu.
This guide has reached the end of its updates as most people are now on the latest DSM update - This guide is correct as of 08/12/2023 however no further updates will be added.


Important or Recent Updates
Historic Updates

What is Watchtower?

Watchtower is an application that watches for updates for all your containers and automatically updates them for you.

Let’s Begin

Watchtower requires access to the Docker socket, we are unable to set this up via the Synology GUI. This means we will be using Docker-Compose.

Docker Compose

We will be using Docker Compose to set up the container. In a nutshell we will be creating a text file (YAML formatted) which tells Docker exactly how we want to set up a specific container.

The next steps can be done either using a code/text editor such as Notepad++ or to keep things simple for this guide we will be using the Synology Text Editor which can be installed from the Package Center.

Install Text Editor from the Package Center

Open up Text Editor and click on File then New to start a new file.

We have a couple of different composes available below the first one is configured to update all running containers at 2am daily (UTC).

YAML
services:
  watchtower:
    image: containrrr/watchtower:latest
    container_name: watchtower
    environment:
      - TZ=YOURTIMEZONE
      - WATCHTOWER_CLEANUP=true
      - WATCHTOWER_INCLUDE_STOPPED=true
      - WATCHTOWER_REVIVE_STOPPED=false
      - WATCHTOWER_SCHEDULE=0 0 2 * * *
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    restart: unless-stopped

As an addition to the method above you can exclude specific containers from updates by adding this line to their yaml (compose) details. This is likely faster than using method 2

YAML
    labels:
      - com.centurylinklabs.watchtower.enable=false

The second has an added section where you can specify the names of the containers you would like to update (use the exact name of the container as per the Synology UI)

You can copy and paste the one you wish to use into the new text file, it is important you don’t change the spacing as YAML has to be formatted correctly in order to be read by Docker Compose.

YAML
services:
  watchtower:
    image: containrrr/watchtower:latest
    container_name: watchtower
    environment:
      - TZ=YOURTIMEZONE
      - WATCHTOWER_CLEANUP=true
      - WATCHTOWER_INCLUDE_STOPPED=true
      - WATCHTOWER_REVIVE_STOPPED=false
      - WATCHTOWER_SCHEDULE=0 0 2 * * *
    command: # add or remove the below as required
      - nzbget
      - overseerr
      - plex
      - prowlarr
      - radarr
      - sonarr
      - tautulli
      - watchtower
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    restart: unless-stopped

Environment Variables

We need to make some changes in order for watchtower to know what time it is where you are and what we want it to do. You can amend these based on your preferences.

VariableValueWhat it does
TZEurope/LondonChange this to your own timezone
WATCHTOWER_CLEANUPtrue or falseWe want to clean up the old docker images, if you don’t turn this on over the course of a few months you will find that the images start to eat a lot of space and they are not even being used. (true or false)
WATCHTOWER_INCLUDE_STOPPEDtrue or falseDo you want to update any stopped containers, the container will stay stopped after being updated (true or false)
WATCHTOWER_REVIVE_STOPPEDtrue or falseIf a stopped container is updated do you want Watchtower to start it up? (true or false)
WATCHTOWER_SCHEDULE0 0 2 * * *Rather than setting the number of seconds to wait between checks you can set a schedule. The default I use is to check at 2am every day, you can work out your own schedule using a cron schedule generator

Your final file should look similar to the one shown below, depending on which version you used above.

Saving the Compose File

We now need to save this file into our docker share

Click on File then Save As, navigate to the ‘docker’ share and you need to change the ‘File name’ to watchtower.yml and save it in the ‘docker’ folder.

SSH and Docker-Compose

It’s time to get logged into you Diskstation via SSH, you can do this in the same way as when you obtained your IDs in the ‘Setting up a restricted Docker user‘ guide.

Once you have logged in you will need to give 2 commands, you can copy and paste these one at a time — you will need to enter your password for the command starting with ‘sudo’

First we are going to change directory to where the watchtower.yml is located, type the below and then press enter.

Bash
cd /volume1/docker

Then we are going to instruct Docker Compose to read the file we created and complete the set-up the container. Again type the below and press enter.

Bash
sudo docker-compose -f watchtower.yml up -d

When the command has completed you should be able to see Watchtower running in the list of containers in the Synology GUI. You can go into the container and within the log you should see that Watchtower is counting down to your next check.

You can now just leave Watchtower running you will never need to manually update your containers again.

FAQ

Q: I keep getting X container has stopped unexpectedly errors!
A: DSM does not know or understand that Watchtower is issuing commands in the background. So it makes the assumption that it was stopped unexpectedly, but we know it was Watchtower doing an update, the same happens if you issue a commands via docker-compose or even Portainer.

Q: Do I need to update Watchtower itself?
A: Nope it updates itself – quite clever really 🙂


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Historic UpdatesDate
New guide released31/12/2021
Added command to only include specific containers (thanks to TimeLord on Discord)01/09/2022
Added notes in relation to updating GlueTUN and Torrents03/12/2022
Added the missing ‘synobridge’ network16/01/2023
Compose version number removed and small wording amendments09/04/2023
Amended the path to save the compose file – this is for security, so the container has no access to the file contents.14/04/2023
Historic Updates
Published inDockerSynologyUpdating Containers 7.1

76 Comments

  1. Dr_Frankenstein Dr_Frankenstein

    Try removing redundant images with sudo docker image prune

    This will remove any unused images.

    Or you can do a complete cleanup with

    sudo docker system prune

    This will remove all unused images, stopped containers and other cached items

  2. Chris Chris

    A big thank you for all you do.
    I have an error with Watchtower, and I don’t know what to do…
    This is an installation with Portainer.
    But I tried in SSH and same problem
    Thank you for your help

    level=warning msg=”Failed to retrieve container image info: Error: No such image: sha256:0d303190802119ec5897f8fa8305f7c2af47b3bd03d206f0dce83c60fe84c6e0″

  3. rfg81 rfg81

    It seems watchtower blocks vlan access when I have it setup as a container in portainer. I’m going to use it as a task to run daily to avoid this problem.

  4. Bryan Bryan

    Well even got this up and running. I almost feel like a docker wizard now. Well I’d be lost without the tutorials! Keep them up. Great stuff!

  5. NewToSyn NewToSyn

    Loving your guides! I have just ordered a synology NAS and will be following them and sending some coffee. Started drafting the docker compose file in preparation. I was trying to figure out how to set watchtower to only update certain containers – their seems to be an environment variable to do this, but I believe I need to set it for each container. I don’t suppose you have done this?

    • Dr_Frankenstein Dr_Frankenstein

      Hey, shout out in Discord if you have any questions when setting up. I have not done what you are after but it looks easy. You add a label of ‘com.centurylinklabs.watchtower.enable’ to you other containers in the compose file and then the Environment Variable WATCHTOWER_LABEL_ENABLE this will then only update those containers.

      Bit hard to explain in the comments.

      • NewToSyn NewToSyn

        Thanks. Will give it a go, think I’ve figured out the label thing. Looks like an even simpler alternative is putting the names of the containers that I want monitored as part of the compose. Just out of interest – do you run your box with separate compose files, or a single one including all? I am unsure whether it’s critical to specify the version or not since some compose files seem to specify use of a different version at the start eg 2 vs 3

        • Dr_Frankenstein Dr_Frankenstein

          I use a single compose file in the /docker share. The version numbers don’t really make any difference to be honest at some point I used 3 and it just stuck. So there might be some slightly different numbers across the guides.

    • Rather than having Watchtower constantly running, I just set up a scheduled task in Synology to run it once a day and clean up after itself once it has completed. Since the container is quite small, it doesn’t have much impact and it also means you don’t need a Compose file or any command line work (although I do run Compose files through Portainer and don’t use Synology’s Docker front end at all).

      docker run –rm –name watchtower \
      -v /var/run/docker.sock:/var/run/docker.sock \
      -e WATCHTOWER_NO_STARTUP_MESSAGE=true \
      -e WATCHTOWER_RUN_ONCE=true \
      -e WATCHTOWER_CLEANUP=true

      • There must be an error in the command.
        It doesn’t run saying something is wrong but I’m not able to figure out the problem

        • His example has hyphens instead of double dashes in a few places. Should be “–rm –name”, not “–rm –name”.

          • Dr_Frankenstein Dr_Frankenstein

            I will see if there is a setting I can change for the comments section, WordPress being derpy and changing

            • – and -rm

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