Add rake docker tasks

lib/tasks/docker.rake

@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+IMAGE_NAME = 'turniere/backend'
+
+namespace :docker do
+  desc 'Build docker image'
+  task :build, [:tag] do |_, args|
+    args.with_defaults(tag: 'latest')
+    sh "docker build -t #{IMAGE_NAME}:#{args.tag} ."
+  end
+
+  desc 'Tag docker image with Travis build number'
+  task :tag do
+    next if ENV['TRAVIS_PULL_REQUEST'] != 'false'
+
+    tag = "build#{ENV['TRAVIS_BUILD_NUMBER']}"
+    sh "docker tag #{IMAGE_NAME} #{IMAGE_NAME}:#{tag}"
+  end
+
+  desc 'Push docker image'
+  task :push do
+    sh "docker push #{IMAGE_NAME}"
+  end
+
+  desc 'Run TravisCI tasks'
+  task travis: %i[build tag push] do
+  end
+end