Access current git commit number from within Heroku app

Question

I know the slug compiler removes the .git directory when creating a heroku slug, but is there any way to configure Heroku so that I can access the currently run

Answer 1

A couple of options...

SOURCE_VERSION environment variable (build-time)

Since 1st April 2015, there's a SOURCE_VERSION environment variable available to builds running on Heroku. For git-pushed builds, this is the git commit SHA-1 of the source being built:

https://devcenter.heroku.com/changelog-items/630

(thanks to @srtech for pointing that out!)

An example of me using that variable in a build - if you look at the HTML served by the deployed app, you'll see the commit id is coming though in an HTML comment near the very bottom: https://gu-who.herokuapp.com/

/etc/heroku/dyno metadata file (run-time)

Heroku have beta functionality to write out a /etc/heroku/dyno metadata file onto your running dyno. If you email support you can probably get added to the beta. Here's a place where Heroku themselves are using it:

https://github.com/heroku/fix/blob/6c8ab7a/lib/heroku_dyno_metadata.rb

The contents look like this:

{
   "dyno":{
      "physical_id":"161bfad9-9e83-40b7-b385-78305db2f168",
      "size":1,
      "name":"run.7145"
   },
   "app":{
      "id":null
   },
   "release":{
      "id":50,
      "commit":"2c3a0b24069af49b3de35b8e8c26765c1dba9ff0",
      "description":null
   }
}

..so release.commit is the field you're after. I used to use this method until the SOURCE_VERSION variable became available.