The docker build cache may consume a large number of filesystem inodes especially if building images containing a large number of files.
The docker build cache can be managed with the docker builder ... CLI commands. If the cache is large, running the prune command can take several minutes.
Here is a shell script to periodically check inode usage in the /var/lib/docker or any other desired directory, and run docker builder prune ... if inode usage exceeds the specified threshold.
An example Kubernetes DaemonSet configuration file shows how this can be run in a docker container on all nodes in a Kubernetes cluster.
One case for use in Kubernetes is with CI/CD agents running inside pods and those agents are connecting to the host's docker daemon to build & push docker container images. Kubernetes itself will garbage collect images and containers that are under K8S control. Other containers and the build cache need to be managed separately. This can help cover the build cache.
The environment variables shown below are available:
| ENVIRONMENT VARIABLE | DEFAULT VALUE | PURPOSE |
|---|---|---|
MOUNTPOINTS |
/var/lib/docker /data/var_lib_docker |
Space separated list of mountpoints to check. Non-existent locations will be silently skipped |
THRESHOLD |
50 |
Minimum percentage inode usage that will trigger pruning |
FILTER |
unused-for=1h |
Value of --filter argument on docker builder prune command |
SLEEP |
600 |
Time to wait between checks. Value in seconds unless suffixed with h or d for hours & days respectively |
REST_TIME |
900 |
Additional time to wait after running a prune. Value in seconds unless suffixed with h or d for hours & days respectively |
IDENTIFIER |
Short hostname (from hostname -s) |
Included in console logs |
HOST_IP |
Empty | Included in console logs |