The Overleaf Toolkit needs to store persistent data, such as the files required to compile LaTeX projects, and the contents of the MongoDB database. This is achieved by mounting a few directories from the host machine into the docker containers, and writing the data to those directories.
The Overleaf container requires a directory in which to store data relating to LaTeX compiles. This directory is set with the OVERLEAF_DATA_PATH variable in config/overleaf.rc.
The MongoDB container, if it is enabled, requires a directory in which to store it's database files, and the same is true of the Redis container. These directories can also be configured in config/overleaf.rc.
Because docker runs as root, the data directories will end up being owned by the root user, even if the toolkit is being used by a non-root user. This is not a problem, but is worth being aware of, if you intend to alter the persistent data from outside of the containers.
Documentation for creating a backup on data can be found in the Developer Wiki.
If you're running Overleaf on Windows or macOS, the mongo service may fail to restart, with an error:
Failed to start up WiredTiger under any compatibility version.
Reason: 1: Operation not permitted
To avoid this error, the data needs to be stored in a volume rather than a bind mounted directory (see the mongo image documentation for more details).
To store data inside Docker volumes mounted inside the MongoDB and Redis containers, add the following to config/docker-compose.override.yml (create this file if it doesn't exist yet):
volumes:
mongo-data:
redis-data:
services:
mongo:
volumes:
- mongo-data:/data/db
redis:
volumes:
- redis-data:/data