Watchtower — Automated Docker Updates on a Synology NAS

Update	Date
New guide released	31/12/2021

Watchtower is an application that watches for updates for all your over containers and automatically updates them for you, this saves you time especially when you have a lot of containers running.

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.

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

You can now copy and paste the details below 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.

version: "3.2"
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

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.

Variable	What it does
TZ=Europe/London	Change this to your own timezone
WATCHTOWER_CLEANUP=true	We 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_STOPPED=true	Do you want to update any stopped containers, the container will stay stopped after being updated (true or false)
WATCHTOWER_REVIVE_STOPPED=false	If a stopped container is updated do you want Watchtower to start it up? (true or false)
WATCHTOWER_SCHEDULE=0 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 everyday, you can work out your own schedule using a cron schedule generator

Your final file should look similar to the one shown below.

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 create a new folder called ‘watchtower’ (lower case)

You need to change the ‘File name’ to watchtower.yml and save it in the ‘watchtower’ 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.

cd /volume1/docker/watchtower

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.

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.

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