heroku outputs “error fetching custom buildpack”, but only sometimes

Question

I have a Django project hosted on Heroku with a buildpack forked from cirlabs/heroku-buildpack-geodjango. Sometimes when I push to Heroku it responds with

Counting objects: 16, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (9/9), done.
Writing objects: 100% (9/9), 790 bytes, done.
Total 9 (delta 7), reused 0 (delta 0)

-----> Heroku receiving push
-----> Fetching custom buildpack... failed
 !     Heroku push rejected, error fetching custom buildpack

To git@heroku.com:taplister-staging.git
 ! [remote rejected] dev -> master (pre-receive hook declined)
error: failed to push some refs to 'git@heroku.com:heroku-app.git'

I'm wondering if this may be an error with the buildpack itself, or if it's something about how Heroku interacts with github?

Oh, also among my heroku config is the buildpack URL

BUILDPACK_URL:              https://github.com/taplister/heroku-buildpack-geodjango

Any insights are greatly appreciated.

Answer 1

This occasionally happens. Since you're using a custom buildpack, each time you push Heroku will download the buildpack over Git, and then use it to process your build.

Sometimes, depending on issues (network latency, temporary downtime, whatever) Heroku just won't be able to finish the Git clone, and will fail with the above error.

This is a known issue, and the only way around it is to retry the push.