* docker: set force=true on remove image to handle images referenced by multiple tags
This PR changes our call of docker client RemoveImage() to RemoveImageExtended with
the Force=true option set. This fixes a bug where an image referenced by more than
one tag could never be garbage collected by Nomad. The Force option only applies to
stopped containers; it does not affect running workloads.
* docker: add note about image_delay and multiple tags
Pulling large docker containers can take longer than the default
context timeout. Without a way to change this it is very hard for
users to utilise Nomad properly without hacky work arounds.
This change adds an optional pull_timeout config parameter which
gives operators the possibility to account for increase pull times
where needed. The infra docker image also has the option to set a
custom timeout to keep consistency.
Fix some docker test flakiness where image cleanup process may
contaminate other tests. A clean up process may attempt to delete an
image while it's used by another test.
* Making pull activity timeout configurable in Docker plugin config, first pass
* Fixing broken function call
* Fixing broken tests
* Fixing linter suggestion
* Adding documentation on new parameter in Docker plugin config
* Adding unit test
* Setting min value for pull_activity_timeout, making pull activity duration a private var
