Why is overlay2 growing in Docker?

Question

Docker

To run multiple replicas, I use docker swarm from one image.
Now I have 6 replicas running and each replica has the --restart=always flag set.
And after a while I noticed that the size of /Containers in the docker is growing strongly, or rather the
/var/lib/docker/overlay2 directory.

Tell me which way to dig, I assume that the dosker does not delete itself when the container is restarted. How can this be overcome? Thank you.

Now the picture is

Answer 1

docker system prune