Pruning Images

Over time Maelstrom nodes may accumulate unused and unwanted Docker images. Eventually this could consume all disk space on a node.

Maelstrom can be optionally configured to periodically remove untagged images and images that are not associated with any components. This feature is disabled by default, but can be easily enabled by setting a single environment variable.

Examples#

Example 1: Remove exited containers and untagged images#

This is similar in behavior to docker system prune. To enable this simply set MAEL_DOCKER_PRUNE_MINUTES to specify the interval this job should run on each Maelstrom node.

# run daily
MAEL_DOCKER_PRUNE_MINUTES=1440

Example 2: Same as #1 plus all images not associated with a component#

# run every 12 hours
MAEL_DOCKER_PRUNE_MINUTES=720
# remove all images NOT associated with a Maelstrom component
MAEL_DOCKER_PRUNE_UNREG_IMAGES=true

This example is a superset of Example 1. In addition to removing exited containers and untagged images Maelstrom will remove all images not associated with a Maelstrom component. For example, if your system has 5 components defined with these image names:

mycorp/web:v1
mycorp/accounting:v2
mycorp/intranet:v2
mycorp/hr
mycorp/api

And your maelstrom node has these images stored locally:

mycorp/web:v1
mycorp/accounting:v1
mycorp/accounting:v2
mycorp/intranet:v1
mycorp/intranet:v2
mycorp/hr
mycorp/api
othercorp/api
redis:3.2

Then these images would be removed:

mycorp/accounting:v1
mycorp/intranet:v1
othercorp/api
redis:3.2

Example 3: Same as #2, but keep some images#

What if you need the redis image and don’t want it deleted? Maelstrom allows you to specify a list of image name patterns to keep.

# run every 12 hours
MAEL_DOCKER_PRUNE_MINUTES=720
# remove all images NOT associated with a Maelstrom component
MAEL_DOCKER_PRUNE_UNREG_IMAGES=true
# comma separated list of names to retain. prefix and suffix * globs
# are supported (but not full regexps)
MAEL_DOCKER_PRUNE_UNREG_KEEP=othercorp/*,redis*

In this configuration only these images would be removed:

mycorp/accounting:v1
mycorp/intranet:v1