Add support to append to existing builder

Signed-off-by: Balasankar 'Balu' C <balasankar@gitlab.com>

lib/gitlab/docker_helper.rb

@@ -62,13 +62,18 @@ class DockerHelper < DockerOperations
     end
 
     def create_builder
-      cleanup_existing_builder
-
       puts "Creating docker builder instance"
+      buildx_command = %W[docker buildx create --bootstrap --use --name omnibus-gitlab-builder-#{Build::Info::CI.commit_ref_slug}]
+
+      if builders_exist?
+        puts "omnibus-gitlab-builder-#{Build::Info::CI.commit_ref_slug} instance already exists. Not attempting to create again but instead appending to it."
+        buildx_command << "--append"
+      end
 
       # TODO: For multi-arch builds, use Kubernetes driver for builder instance
-      _, stdout_stderr, status = Open3.popen2e(*%W[docker buildx create --bootstrap --use --name omnibus-gitlab-builder-#{Build::Info::CI.commit_ref_slug}])
+      raise "Using Kubernetes cluster for buildx is not currently supported." if Gitlab::Util.get_env('DISABLE_BUILDX_CLUSTER') && Gitlab::Util.get_env('DISABLE_BUILDX_CLUSTER') != 'true'
 
+      _, stdout_stderr, status = Open3.popen2e(*buildx_command)
       return if status.value.success?
 
       puts "Creating builder instance failed."
@@ -76,10 +81,15 @@ class DockerHelper < DockerOperations
       raise
     end
 
-    def cleanup_existing_builder
-      puts "Cleaning any existing builder instances."
+    def builders_exist?
       _, _, status = Open3.popen2e(*%W[docker buildx ls | grep omnibus-gitlab-builder-#{Build::Info::CI.commit_ref_slug}])
-      unless status.value.success?
+      status.value.success?
+    end
+
+    def cleanup_existing_builder
+      puts "Cleaning existing builder instances."
+
+      unless builders_exist?
         puts "omnibus-gitlab-builder-#{Build::Info::CI.commit_ref_slug} instance not found. Not attempting to clean."
         return
       end

spec/lib/gitlab/docker_helper_spec.rb

@@ -106,7 +106,6 @@ RSpec.describe DockerHelper do
 
   describe '.create_builder' do
     before do
-      allow(described_class).to receive(:cleanup_existing_builder).and_return(true)
       stub_env_var('CI_COMMIT_REF_SLUG', 'feature-branch')
 
       stdout_stderr_mock = double(gets: nil)
@@ -114,10 +113,28 @@ RSpec.describe DockerHelper do
       allow(Open3).to receive(:popen2e).with("docker", "buildx", "create", any_args).and_return([nil, stdout_stderr_mock, status_mock])
     end
 
-    it 'calls docker buildx create command with correct arguments' do
-      expect(Open3).to receive(:popen2e).with(*%w[docker buildx create --bootstrap --use --name omnibus-gitlab-builder-feature-branch])
+    context 'when builder already exists' do
+      before do
+        allow(described_class).to receive(:builders_exist?).and_return(true)
+      end
 
-      described_class.create_builder
+      it 'calls docker buildx create command with append argument' do
+        expect(Open3).to receive(:popen2e).with(*%w[docker buildx create --bootstrap --use --name omnibus-gitlab-builder-feature-branch --append])
+
+        described_class.create_builder
+      end
+    end
+
+    context 'when builder does not already exist' do
+      before do
+        allow(described_class).to receive(:builders_exist?).and_return(false)
+      end
+
+      it 'calls docker buildx create command without append argument' do
+        expect(Open3).to receive(:popen2e).with(*%w[docker buildx create --bootstrap --use --name omnibus-gitlab-builder-feature-branch])
+
+        described_class.create_builder
+      end
     end
   end