build-packer-templates.rb

def link_to(url, content = nil)
  if ENV["BUILDKITE"]
    "\e]1339;url=#{url.gsub(";", "%3b")}#{";content=#{content.gsub(";", "%3b")}" if content}\a"
  else
    url
  end
end

def system!(*args)
  system(*args) or fail("Command exited with status #{$?.exitstatus}: #{args.join(" ")}")
end

def capture!(*args)
  IO.popen(args, &:read).tap do
    $?.success? or fail("Command exited with status #{$?.exitstatus}: #{args.join(" ")}")
  end
end

def meta_data_get(name)
  capture!("buildkite-agent", "meta-data", "get", name.to_s).chomp
end

def meta_data_set(name, value)
  system!("buildkite-agent", "meta-data", "set", name.to_s, value.to_s)
end

require "buildkit"

token = ENV.fetch("BUILDKITE_TOKEN")
$buildkit = Buildkit.new(token: token)

templates = []

if ENV["PACKER"] && %w(0 n no f false).include?(ENV["PACKER"].strip.downcase)
  puts "--- :fast_forward: You've asked me not to build anything"
elsif ENV["PACKER"] && %w(1 y yes t true).include?(ENV["PACKER"].strip.downcase)
  puts "--- :allthethings: You've asked me to build everything"

  templates = Dir["packer/*.json"].map { |path| File.basename(path, ".json") }
elsif ENV["PACKER"] && !ENV["PACKER"].strip.empty?
  puts "--- :bow: You've asked me to build #{ENV["PACKER"]}"

  templates = ENV["PACKER"].split(",").map(&:strip)
else
  puts "+++ :thinking_face: Seeing if we need to build new images"

  organization = ENV.fetch("BUILDKITE_ORGANIZATION_SLUG")
  pipeline = ENV.fetch("BUILDKITE_PIPELINE_SLUG")

  branch = ENV.fetch("BUILDKITE_BRANCH")
  commit = ENV.fetch("BUILDKITE_COMMIT")

  Dir["packer/*.json"].each do |path|
    template = File.basename(path, ".json")
    previous_build = nil

    # If this is not the master branch then it's probably a pull request
    # to look at the history of this branch for a packer build and diff
    # from the previously built commit
    if branch != "master"
      previous_build = $buildkit.pipeline_builds(organization, pipeline, branch: branch, "meta_data[packer:build:#{template}]" => "true", page: 1, per_page: 1).first
    end

    # If this is master and we're running a pull request merge commit and
    # the merged branch has a built packer image and nothing in packer
    # has changed on master since this branch started then we can use the
    # already-built image.
    #
    # Useful when the pull request image has already been tested and
    # we're just merging to promote that image into production.
    if !previous_build and
        branch == "master" and
        %r{Merge pull request #(?:\d+) from (?:[^/]+)/(?<previous_branch>.+)} =~ capture!("git", "show", commit, "--format=format:%s").chomp and
        system("git", "diff", "--quiet", "#{capture!("git", "merge-base", "HEAD^1", "HEAD^2").chomp}...#{commit}^", "packer")
      previous_build = $buildkit.pipeline_builds(organization, pipeline, branch: previous_branch, "meta_data[packer:build:#{template}]" => template, page: 1, per_page: 1).first
    end

    # Otherwise maybe there's a recent master build which we can use as a base for comparison
    if !previous_build
      previous_build = $buildkit.pipeline_builds(organization, pipeline, branch: "master", "meta_data[packer:build:#{template}]" => "true", page: 1, per_page: 1).first
    end

    # If we found a previous build then see if there have been any changes
    if previous_build
      # Make sure we have the commit we want to diff against
      unless system "git", "cat-file", "-e", "#{previous_build.commit}^{commit}"
        system! "git", "fetch", "origin", previous_build.commit
      end

      # Has this template been changed since then?
      #
      # XXX: This only considers the template file, not the scripts or
      # any files for copying like services, etc. You must bump the
      # template content to trigger an automatic packer build.
      #
      if not system("git", "diff", "--quiet", "--diff-filter", "ACMR", "#{previous_build.commit}...#{commit}", "--", "packer/#{template}.json")
        puts "#{template} has been built on #{previous_build.branch} at #{previous_build.commit} in #{link_to(previous_build.web_url, "build #{previous_build.number}")} but packer template has changed, building."

        templates << template
      else
        puts "#{template} has been built on #{previous_build.branch} at #{previous_build.commit} in #{link_to(previous_build.web_url, "build #{previous_build.number}")}."
      end
    else
      puts "#{template} has never been built, building."

      # We couldn't find a single build of this template! Definitely build it.
      templates << template
    end
  end
end

templates.each do |template|
  puts "+++ :thinking_face: Building #{template}"

  system! "packer", "build", "packer/#{template}.json"

  meta_data_set "packer:build:#{template}", "true"
end