Asynchronous image removal would remove intermediate build images during the build process, causing intermittent build failures for users of multi-stage dockerfiles. While we still remove intermediate docker images that may be used in the current build, we now do so during the deploy, ensuring that there are no intermediate build failures in the future.
Closes#3474
As this trigger is always in the execution path, `plugn` starts and expensively checks to see if it can execute the trigger. Rather than call this on every invocation, skip the trigger if no non-core implementation exists.
This is a "one-shot" ability, meaning that it is highly discouraged for multiple plugins to implement the triggers.
The `builder-create-dokku-image` trigger is meant to modify the base DOKKU_IMAGE that will be used to build an application. A good use of the hook is to inject system packages by:
- calculating an image tag from the set of system packages
- checking that the image doesnt already exist
- creating the image if it does not
As the output is sent to stdout, we have to find an alternative way of fetching the new DOKKU_IMAGE. The `builder-dokku-image` trigger can output an image tag based on the calculated image tag. If no tag is output, then the DOKKU_IMAGE is used as is.
Using this pattern, users can efficiently modify the base image in use for an app without duplicating the work on every push. This is especially useful for package installation, where packages are required for app building, but may take a long time and can be error prone.
A builder plugin implements some method for 'building' artifacts from a given source code archive. This refactor moves the majority of the image building code into separate plugins, allowing us to implement other builders, but also simplifying the common pugin codebase.
Also move the pre-build-buildpack hook from the build-env plugin to builder-herokuish.
This reduces duplication and allows users to rely on global arguments to generate most labels needed.
The 'commit' command cannot have global arguments because the whitespace within the label change breaks string-based interpolation, and shell arrays cannot be exported.
The plugin creation docs were hard to follow, unnecessarily complicating issues for developers. The new format should make the recommendations clear, and align examples with the core code.
[ci skip]
