hot-code-reloading.md

Hot code-reloading

By default, apps are restarted when new versions are deployed. This is to make it easy for people to deploy apps quickly with quick setup.

To enable

• Set the deploy_type variable to upgrade in your project's playbooks/vars/main.yml file
• Everytime you deploy, update the app's version in the project's mix.exs

Automatic versioning using git

For hot code-reloading, the app's version needs to be updated in mix.exs for every deploy. That can get repeatitive, since hobby projects are updated & deployed frequently. We've got a workaround for that. We'll use automatic versioning based on git commit SHAs. Technical details are explained in this blog post.

• Change the following in mix.exs

def project do
  [app: :hello_phoenix,
   version: "1.4.1",
   elixir: "~> 1.0",
   ...

to look like the following

def project do
  {result, _exit_code} = System.cmd("git", ["rev-parse", "HEAD"])

  # We'll truncate the commit SHA to 7 chars. Feel free to change
  git_sha = String.slice(result, 0, 7)

  [app: :hello_phoenix,
   version: "1.4.1-#{git_sha}",
   elixir: "~> 1.0",
   ...

That just changes the version to use the git commit SHA.