I use Docker for my CI pipeline: testing, building, etc. Everything that is built successfully, is packed as a Docker image and is pushed on a private Docker registry. Before long I was having space issues (which turned out to not to be caused by the registry) and decided to purge all images older than 3 months.
I decided on a simple program with the following requirements:
- It should be a single binary with no dependencies
- It should work with remote (non-local) registries
- It should conform to Docker APIs (no dirty hacking!)
- It should be possible to remove images by age
- It should always keep the latest image
Requirement 1. and 2. make sure that no other dependencies/runtime env is needed and the housekeeping can be done remotely. Requirement 3. makes sure that the communication procedure with the registry is undesrstood correctly! Requirement 4. allows fine-grain filtering. Requirement 5. makes sure that in the worst case, at least one image per repository stays on the server.
There are similar projects implemented in python, ruby, etc. As I wanted to have the housekeeping locally on my Docker registry server, I deemed it utmost unnecesary to have python, etc. installed on my production server just to remove old Docker images from the registry. And that’s how
deckschrubber was born.
I chose Go as it allows building cross platform executable (also see Go CGO) and as Docker registry itself is implemented in Go (Req. 1.). Go packages from Docker registry are used to make sure the program conforms to the API (Req. 2. and 3.).
Filtering (Req. 4 und 5.) is done as follows:
- The list of repositories is fetched from the registry (e.g. from
- The list of images of each repository is fetched
- Blob details for each image is fetched (this contains creation date)
- A sorted (by date) list of images for each repository is created
- For each respository, images older than the given age (except latest image) are removed
NOTE: to have the deletion take effect immediately, the garbage collection of the registry has to be triggered:
registry garbage-collect /etc/docker/registry/config.yml
It is assumed that the configuration for the registry is available under the default path
git clone https://github.com/fraunhoferfokus/deckschrubber.git cd deckschrubber go get ./... go install $GOPATH/bin/deckschrubber -registry http://localhost:5000 -repos 25 -day 14 -dry
For details on arguments and more examples, checkout the project page.