Docker redis backup

Question

I am looking at this example

docker run --rm --volumes-from myredis -v $(pwd)/backup:/backup debian cp /data/dump.rdb /backup/

from Using Docker book.

Why do we need --rm flag?

Why do we have --volumes-from?

Answer 1

The idea here is that

• you have a redis container named myredis which has some volumes for persistent storage (that you'd like to backup).
• you run a temporary debian container that will save the backup to your_current_dir/backup and get removed.

---

1. docker run --rm ... debian runs the container and removes it after it exits
2. --volumes-from myredis this way the debian container will have access to the database
3. -v $(pwd)/backup:/backup this second volume is used to put the backup at your current dir $(pwd)/backup. If it wasn't used, the backup would have only been copied to /backup (inside the container) and later been removed together with the container. This way the backup persists.
4. cp /data/dump.rdb /backup/ copies the actual files

Answer 2

The --rm flag tells Docker Engine to remove the container once it exits. Without this flag, you need to manually remove the container after you stop it.

The --volumes-from flag mounts all the defined volumes from the referenced containers, it ensures the two containers mounts same volumes.