Description
I recently ran into buildpack IO errors during a pack build that turned out to be due to disk space exhaustion on the macOS Docker Desktop created VM - caused by leftover Docker volumes used by Pack for caching.
There were ~800 named Docker volumes that consumed 40GB of disk space, of form:
$ docker volume ls
DRIVER VOLUME NAME
local pack-cache-library_libcnbtest_abnaipzkqlhfeopwdzgpcmwnldonle_latest-ce76e11c69c4.build
local pack-cache-library_libcnbtest_abnaipzkqlhfeopwdzgpcmwnldonle_latest-ce76e11c69c4.launch
local pack-cache-library_libcnbtest_actqilpclbkigdmjhdrhgnuwgealsm_latest-a44e7557da8c.build
local pack-cache-library_libcnbtest_actqilpclbkigdmjhdrhgnuwgealsm_latest-a44e7557da8c.launch
local pack-cache-library_libcnbtest_actyjtmpayftrpdhfehpwefuffycaf_latest-d0ec397b5241.build
local pack-cache-library_libcnbtest_actyjtmpayftrpdhfehpwefuffycaf_latest-d0ec397b5241.launch
...
For normal (non-integration testing) usage of Pack CLI, one wouldn't end up with hundreds of these volumes, since caches are re-used/replaced for the same output image name. The reason we end up with hundreds when using libcnb-test is that it uses a random image name each time (which is the right thing for it to do), but whilst it deletes the images at the end of each test, it doesn't currently delete the image's associated Pack cache volumes.
I've started a discussion ups
5FAE
tream about some potential improvements upstream (for example, adding pack cache prune commands or similar, and also asking why Pack is creating these volumes for layers that also exist in the final app image):
https://cloud-native.slack.com/archives/C0331B61A1Y/p1683817627443339
However, libcnb-test will need to handle this even with those improvements upstream.
To avoid this issue, libcnb-test can use the new --cache argument to pack build, and either:
- Continue to use volume-based caching, but pass in an explicit (and random) volume name, that
libcnb-testcan then remove whenTestContextis dropped. (For example:--cache='type=build;format=volume;name=<volume-name>;type=launch;format=volume;name=<volume-name>') - Or, switch to bind mount based caching, and pass in a temporary directory as the cache location, that
libcnb-testcan then remove whenTestContextis dropped. (For example:--cache='type=build;format=bind;source=<a-tmp-dir>;type=launch;format=bind;source=<a-tmp-dir>')