Support for post deployment migrationsbackground-migrations

These are regular Rails migrations that are executed by default. A user
can opt-out of these migrations by setting an environment variable
during the deployment process.

Fixes gitlab-org/gitlab-ce#22133

1 files changed, 22 insertions, 0 deletions

diff --git a/generator_templates/rails/post_deployment_migration/migration.rb b/generator_templates/rails/post_deployment_migration/migration.rb
new file mode 100644
index 00000000000..1a7b8d5bf35
--- /dev/null
+++ b/generator_templates/rails/post_deployment_migration/migration.rb
@@ -0,0 +1,22 @@
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class <%= migration_class_name %> < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  # When using the methods "add_concurrent_index" or "add_column_with_default"
+  # you must disable the use of transactions as these methods can not run in an
+  # existing transaction. When using "add_concurrent_index" make sure that this
+  # method is the _only_ method called in the migration, any other changes
+  # should go in a separate migration. This ensures that upon failure _only_ the
+  # index creation fails and can be retried or reverted easily.
+  #
+  # To disable transactions uncomment the following line and remove these
+  # comments:
+  # disable_ddl_transaction!
+
+  def change
+  end
+end