composing multiple buildpacks to advance alm ideas

James Bayer

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Oct 6, 2013, 4:15:34 AM10/6/13

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i did a brief experiment tonight with a multi buildpack [1] that i referenced in the ALM ideas document [2].

i created an empty directory and in that directory i created a .buildpacks file with 2 entries.

1st entry - a buildpack url of a buildpack that clones one of my github repos. the repo it's cloning is currently hardcoded to a sinatra app [3], but can be easily changed to a different git location and use credentials, both retrieved from env variables.

2nd entry - the cf ruby buildpack

then i pushed the app with --buildpack and referenced the multi-buildpack url and that was it. it worked like a charm [4]

this shows that we can easily use a buildpack that looks at env variables and then pulls in app source files or binaries from other locations like scm or blob storage, and then still run a buildpack on those files that are pulled in. we can now imagine a pipeline for a particular app with multiple copies, each pulling from different branches/tags of an scm system very easily with minor config variation. i believe this will help us experiment more with alm ideas.

this also shows that we should be able to use this approach to pull in code from repos that may not be public, because we can use a public configurable app-source-retriever-buildpack to pull in non-public stuff leveraging private non-public env variables.

i thought i'd share this approach in case it create some additional ideas for others.

[1] https://github.com/ddollar/heroku-buildpack-multi

[2] https://docs.google.com/a/gopivotal.com/document/d/1pOTLLm2oAm1L2WG5W220kYXJYHcU2RM-8kvvOyY1kcQ/edit#heading=h.ngubbq50ycrf

[3] https://github.com/jbayer/null-buildpack/blob/master/bin/compile

[4] https://gist.github.com/jbayer/6850923

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Thank you,

James Bayer