Read Git Revision (Hash) in Elixir

[nelsonic]

I would like to display the git revision hash when visiting a url in an application
so that everyone on the project knows exactly which version of the app
is in "staging" or production.

e.g visiting: https://www.healthlocker.uk/_version

healthlocker/healthlocker@cc66a3c

Note: currently visiting this url shows an error page:

We made the Git Revision available in dwyl/aws-lambda-deploy/lib/utils.js#L80-L81
So it's a matter of running a similar command in Elixir and returning that when visiting the route.

Todo

• run an Elixir command/script to get the git revision
• create a route in basic Phoenix app that returns the git revision
• determine if the git revision is available in an elixir app that has been deployed with edeliver (I don't see a reason why not, we need to be certain)

[nelsonic]

https://stackoverflow.com/questions/22594988/run-shell-commands-in-elixir

git rev-parse HEAD

so the Git Revision in Elixir is:

System.cmd("git", ["rev-parse", "HEAD"])

iex demo:

[nelsonic]

surprisingly easy even with my paltry Elixir/Phoenix skills ... 😮

add the following handler to: web/controllers/page_controller.ex:

  def git_revision_hash(conn, _params) do
    {rev, i} = System.cmd("git", ["rev-parse", "HEAD"])
    text conn, String.replace(rev, "\n", "")
  end

add route to /router.ex:

get "/_version", PageController, :git_revision_hash

Result:

Which is exactly what I wanted. ✅

[nelsonic]

Learned how to render text from:
https://stackoverflow.com/questions/38601617/whats-the-most-minimalistic-way-to-render-ok-in-elixir-phoenix

[nelsonic]

sadly, as I feared, the release generated by distillery does not include the .git history!
so:

fatal: Not a git repository (or any of the parent directories): .git

So we're back to the drawing board on this ... 😢

[nelsonic]

  def git_revision_hash(conn, _params) do
    IO.inspect(System.cmd("pwd", []))
    {ls, _} = IO.inspect(System.cmd("ls", ["-a"]))

    ls = String.split(ls, "\n")
    IO.inspect ls

    unless Enum.member?(ls, ".git") do
      File.cd("./builds")
      IO.inspect(System.cmd("pwd", []))
    end

    {rev, _} = System.cmd("git", ["rev-parse", "HEAD"])
    IO.puts(String.replace(rev, "\n", ""))
    text conn, String.replace(rev, "\n", "")
  end

still debugging it, will reduce debug lines once it's working.

[nelsonic]

Result!

7cb64a0be4bd7346ee4a4cc2bf770e401f9f76c9

This Git Hash corresponds to this commit: nelsonic/hello_world_edeliver@7cb64a0

So it's trivial to see exactly which version of the project is running in a given environment!

[nelsonic]

Got it working in: dwyl/learn-devops#19 (comment)