Persist the State of the SuperLink

By default, the Flower SuperLink keeps its state in-memory. When using the Docker flag --rm, the state is not persisted between container starts.

If you want to persist the state of the SuperLink on your host system, all you need to do is specify a directory where you want to save the file on your host system and a name for the database file.

By default, the SuperLink container runs with a non-root user called app with the user ID 49999. When working with Docker on Linux, it is recommended to create a new directory and set the user ID to 49999 to ensure the mounted directory has the proper permissions.

If you later want to delete the directory, you can change the user ID back to the current user ID by running sudo chown -R $USER:$(id -gn) state.

Example

In the example below, we create a new directory called state, change the user ID and tell Docker via the flag --volume to mount the local state directory into the /app/state directory of the container. Lastly, we use the flag --database to specify the name of the database file.

$ mkdir state
$ sudo chown -R 49999:49999 state
$ docker run --rm \
     --volume ./state/:/app/state flwr/superlink:1.18.0 \
     --database state.db \
     <additional-args>

As soon as the SuperLink starts, the file state.db is created in the state directory on your host system. If the file already exists, the SuperLink tries to restore the state from the file. To start the SuperLink with an empty database, ensure that there is no database called state.db in the state directory (rm state.db) before you execute the docker run command above.