Disk Clean-Up
Docker uses the disk in different ways:
Docker Images
Saving your images: images are compressed files with your built source-code that you deployed to the server. Every time you deploy a new version of your code, Docker builds a new image for the new version and keeps the old image by default. If you want to clean up all "unused" images on your server, run
docker container prune --force
docker image prune --all
Important Note: Use this approach only if you have a Docker registry set up (local or remote). This is due to an existing bug in Docker, see here for more details on the problem and also see the related Docker Issue
Docker Volumes
Volumes, aka "Persistent Directories". When you create an app with persistent data, like a database, you will assign it a persistent directory. When you change the persistent directory, or when you delete your app, you don't need the volumes anymore. Cleaning up orphaned volumes are tricky. If you have a useful volume for an app that is "currently" crashing and not-running, that volume is considered as "orphaned" by Docker :( So, to safely clean up orphaned volumes, first, check to see if all your services are running by:
docker service ls
Under REPLICAS, you should see 1/1, 2/2 and etc. If you see a service that is not running, then do not proceed! Otherwise, go head and clean-up orphaned volumes by:
docker volume prune
Alternatively, you can first list all volumes, and delete only the ones that you don't want:
docker volume ls # lists all volumes
docker volume rm volume-name-goes-here # removes a specific volume