Building and running Anki sync server in Docker

This is an example Dockerfile contributed by an Anki user, which shows how you can run a self-hosted sync server, similar to what AnkiWeb.net offers.

Building and running the sync server within a container has the advantage of fully isolating the build products and runtime dependencies from the rest of your system.

Requirements

• Docker

Aspect	Dockerfile	Dockerfile.distroless
Shell & Tools	✅ Includes shell and tools	❌ Minimal, no shell or tools
Debugging	✅ Easier debugging with shell and tools	❌ Harder to debug due to minimal environment
Health Checks	✅ Supports complex health checks	❌ Health checks need to be simple or directly executable
Image Size	❌ Larger image size	✅ Smaller image size
Customization	✅ Easier to customize with additional packages	❌ Limited customization options
Attack Surface	❌ Larger attack surface due to more installed packages	✅ Reduced attack surface
Libraries	✅ More libraries available	❌ Limited libraries
Start-up Time	❌ Slower start-up time due to larger image size	✅ Faster start-up time
Tool Compatibility	✅ Compatible with more tools and libraries	❌ Compatibility limitations with certain tools
Maintenance	❌ Higher maintenance due to larger image and dependencies	✅ Lower maintenance with minimal base image
Custom uid/gid	✅ It’s possible to pass in PUID and PGID	❌ PUID and PGID are not supported

Building image

To proceed with building, you must specify the Anki version you want, by replacing <version> with something like 24.11 and <Dockerfile> with the chosen Dockerfile (e.g., Dockerfile or Dockerfile.distroless)

The --platform option specifies which systems the image will be able to run on after it has been built. This is helpful in scenarios where you are building the image on one architecture (eg: an M series Mac) but running the image on another architecture (eg: x86 Linux server).

• linux/amd64 is for x86 linux systems (Images built with this option will work on Windows as well through WSL2 which is included with Docker Desktop)
• linux/arm64 is for ARM systems (eg: M series Macs)

On Linux systems, you will have to configure a custom builder which supports ARM builds first as shown below. You can then run the Mac build command in the next step.

# Configuring multiplatform builder and activating it
docker buildx create --name multiplatform-builder --driver docker-container --driver-opt default-load=true --bootstrap --use

On M-series Macs running Docker Desktop, you can build for both platforms using the default builder by running the command below:

# Execute this command from this directory
docker buildx build -f <Dockerfile> --platform linux/amd64,linux/arm64 --no-cache --build-arg ANKI_VERSION=<version> -t anki-sync-server .

If the build fails with Resource Exhausted:.... cannot allocate memory, go to Docker Desktop > Settings > Resources and increase the memory limit.

If you are unsure of what platform your system is, just run the command below without the platform option.

# Execute this command from this directory
docker buildx build -f <Dockerfile> --no-cache --build-arg ANKI_VERSION=<version> -t anki-sync-server .

Run container

Once done with build, you can proceed with running this image with the following command:

# this will create anki server
docker run -d \
    -e "SYNC_USER1=admin:admin" \
    -p 8080:8080 \
    --mount type=volume,src=anki-sync-server-data,dst=/anki_data \
    --name anki-sync-server \
    anki-sync-server

If the image you are using was built with Dockerfile you can specify the PUID and PGID env variables for the user and group id of the process that will run the anki-sync-server process. This is valuable when you want the files written and read from the /anki_data volume to belong to a particular user/group e.g. to access it from the host or another container. Note the the ids chosen for PUID and PGID must not already be in use inside the container (1000 and above is fine). For example add -e "PUID=1050" and -e "PGID=1050" to the above command.

If you want to have multiple Anki users that can sync their devices, you can specify multiple SYNC_USER as follows:

# this will create anki server with multiple users
docker run -d \
    -e "SYNC_USER1=admin:admin" \
    -e "SYNC_USER2=admin2:admin2" \
    -p 8080:8080 \
    --mount type=volume,src=anki-sync-server-data,dst=/anki_data \
    --name anki-sync-server \
    anki-sync-server

Moreover, you can pass additional env vars mentioned here. Note that SYNC_BASE and SYNC_PORT will be ignored. In the first case for safety reasons, to avoid accidentally placing data outside the volume and the second for simplicity since the internal port of the container does not matter given that you can change the external one.

Upgrading

If your image was built after January 2025 then you can just build a new image and start a new container with the same configuration as the previous container. Everything should work as expected.

If the image you were running was built before January 2025 then it did not contain a volume, meaning all syncserver data was stored inside the container. If you discard the container, for example because you want to build a new container using an updated image, then your syncserver data will be lost.

The easiest way of working around this is by ensuring at least one of your devices is fully in sync with your syncserver before upgrading the Docker container. Then after upgrading the container when you try to sync your device it will tell you that the server has no data. You will then be given the option of uploading all local data from the device to syncserver.