Add initial support for fetching govuk-guix revisions on remote hosts

This begins to remote the restriction of having to have Guix installed
locally.

3 files changed, 64 insertions, 14 deletions

diff --git a/app/controllers/govuk_guix/revisions_controller.rb b/app/controllers/govuk_guix/revisions_controller.rb
index 1e311eb..f7c7f56 100644
--- a/app/controllers/govuk_guix/revisions_controller.rb
+++ b/app/controllers/govuk_guix/revisions_controller.rb
@@ -26,7 +26,19 @@ class GovukGuix::RevisionsController < ApplicationController
   def enqueue_fetch_revision
     revision = params.require('revision')
 
-    GovukGuix::FetchRevisionJob.enqueue(revision)
+    # Attempt to check if this can be performed locally
+    if File.exist? '/var/guix/daemon-socket/socket'
+      options = {}
+    else
+      # Assume that the AWS backend is in use
+      backend = Backends::TerraformAws.first
+
+      options = {
+        run_remotely_on_host: "ubuntu@guix-daemon.#{backend.domain}"
+      }
+    end
+
+    GovukGuix::FetchRevisionJob.enqueue(revision, options)
 
     flash[:info] = "Fetching govuk-guix revision (#{revision})..."
     redirect_to setup_path
diff --git a/app/jobs/govuk_guix/fetch_revision_job.rb b/app/jobs/govuk_guix/fetch_revision_job.rb
index 2787156..d3f11bf 100644
--- a/app/jobs/govuk_guix/fetch_revision_job.rb
+++ b/app/jobs/govuk_guix/fetch_revision_job.rb
@@ -24,26 +24,22 @@ class GovukGuix::FetchRevisionJob < Que::Job
   extend EnqueuedJobs
   include ::ShellUtils
 
-  REPOSITORY_DIRECTORY = 'tmp/cache/govuk-guix'.freeze
-
   @retry_interval = 30
 
-  def run(commit_hash)
-    repository.fetch
-
-    sha = repository.object(commit_hash).sha
+  def run(commit_hash, options = {})
+    remote_host = options[:run_remotely_on_host]
 
-    repository.checkout(sha)
+    fetch_and_checkout(commit_hash, remote_host)
 
     command = [
-      "#{REPOSITORY_DIRECTORY}/guix-pre-inst-env",
+      "#{@repository_directory}/guix-pre-inst-env",
       'guix',
       'build',
       '-e',
       '(begin (use-modules (gds packages govuk)) (current-govuk-guix))'
     ]
 
-    output = run_command(*command)
+    output = run_command(*command, run_remotely_on_host: remote_host)
 
     store_path = output.last.strip
     logger.debug(self.class) { "store_path: #{store_path}" }
@@ -55,12 +51,53 @@ class GovukGuix::FetchRevisionJob < Que::Job
     )
   end
 
+  def fetch_and_checkout(commit_hash, remote_host)
+    if remote_host
+      @repository_directory = '/tmp/govuk-guix'
+
+      run_command(
+        "/bin/sh",
+        "-c",
+        "if cd '#{@repository_directory}';"\
+        "then git fetch;"\
+        "else "\
+        "git clone #{self.class.repository_remote_location} '#{@repository_directory}';"\
+        "fi",
+        run_remotely_on_host: remote_host
+      )
+
+      sha = run_command(
+        "/bin/sh",
+        "-c",
+        "cd '#{@repository_directory}';"\
+        "git rev-list -n 1 '#{commit_hash}'",
+        run_remotely_on_host: remote_host
+      ).last.strip
+
+      run_command(
+        "/bin/sh",
+        "-c",
+        "cd '#{@repository_directory}';"\
+        "git checkout #{sha}",
+        run_remotely_on_host: remote_host
+      )
+    else
+      @repository_directory = 'tmp/cache/govuk-guix'
+
+      repository.fetch
+
+      sha = repository.object(commit_hash).sha
+
+      repository.checkout(sha)
+    end
+  end
+
   def repository
     @_repository ||= begin
-      if File.exist? REPOSITORY_DIRECTORY
-        Git.open(REPOSITORY_DIRECTORY, log: Rails.logger)
+      if File.exist? @repository_directory
+        Git.open(@repository_directory, log: Rails.logger)
       else
-        Git.clone(self.class.repository_remote_location, REPOSITORY_DIRECTORY)
+        Git.clone(self.class.repository_remote_location, @repository_directory)
       end
     end
   end
diff --git a/test/controllers/govuk_guix/revisions_controller_test.rb b/test/controllers/govuk_guix/revisions_controller_test.rb
index 51ca048..6f08489 100644
--- a/test/controllers/govuk_guix/revisions_controller_test.rb
+++ b/test/controllers/govuk_guix/revisions_controller_test.rb
@@ -19,7 +19,8 @@ class GovukGuix::RevisionsControllerTest < ActionDispatch::IntegrationTest
   test 'enqueue_fetch_revision' do
     revision = 'test-revision'
 
-    GovukGuix::FetchRevisionJob.expects(:enqueue).with(revision)
+    Guix.stubs(:available_locally?).returns(true)
+    GovukGuix::FetchRevisionJob.expects(:enqueue).with(revision, {})
 
     post(
       enqueue_fetch_govuk_guix_revision_path,