In order to implement and test this feature, you need to first [set up Geo locally](https://gitlab.com/gitlab-org/gitlab-development-kit/blob/main/doc/howto/geo.md).
There are three main sections below. It is a good idea to structure your merge requests this way as well:
1. Modify database schemas to prepare to add Geo support for Cool Widgets
1. Implement Geo support of Cool Widgets behind a feature flag
1. Release Geo support of Cool Widgets
It is also a good idea to first open a proof-of-concept merge request. It can be helpful for working out kinks and getting initial support and feedback from the Geo team. As an example, see the [Proof of Concept to replicate Pipeline Artifacts](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/56423).
You can look into the following examples of MRs for implementing replication/verification for a new blob type:
- [Add db changes](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/60935) and [add verification for MR diffs using SSF](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/63309)
- [Verify Terraform state versions](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/58800)
### Modify database schemas to prepare to add Geo support for Cool Widgets
You might do this section in its own merge request, but it is not required.
#### Add the registry table to track replication and verification state
Geo secondary sites have a [Geo tracking database](https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/development/geo.md#tracking-database) independent of the main database. It is used to track the replication and verification state of all replicables. Every Model has a corresponding "registry" table in the Geo tracking database.
- [ ] Create the migration file in `ee/db/geo/migrate`:
- [ ] Replace the contents of the migration file with the following. Note that we cannot add a foreign key constraint on `cool_widget_id` because the `cool_widgets` table is in a different database. The application code must handle logic such as propagating deletions.
- [ ] If deviating from the above example, then be sure to order columns according to [our guidelines](https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/development/ordering_table_columns.md).
The Geo primary site needs to checksum every replicable so secondaries can verify their own checksums. To do this, Geo requires fields on the Model. Add verification state fields to a separate table. Consult a database expert if needed.
- [ ] If deviating from the above example, then be sure to order columns according to [our guidelines](https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/development/ordering_table_columns.md).
- [ ] If `cool_widgets` is a high-traffic table, follow [the database documentation to use `with_lock_retries`](https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/development/migration_style_guide.md#when-to-use-the-helper-method)
- [ ] Ensure `CoolWidget.replicables_for_current_secondary` is well-tested. Search the codebase for `replicables_for_current_secondary` to find examples of parameterized table specs. You may need to add more `FactoryBot` traits.
- [ ] Add the following shared examples to `ee/spec/models/ee/cool_widget_spec.rb`:
```ruby
include_examples 'a replicable model with a separate table for verification state' do
let(:verifiable_model_record) { build(:cool_widget) } # add extra params if needed to make sure the record is included in `available_verifiables`
let(:unverifiable_model_record) { build(:cool_widget) } # add extra params if needed to make sure the record is NOT included in `available_verifiables`
- [ ] Create `ee/app/replicators/geo/cool_widget_replicator.rb`. Implement the `#carrierwave_uploader` method which should return a `CarrierWave::Uploader`, and implement the class method `.model` to return the `CoolWidget` class:
```ruby
# frozen_string_literal: true
module Geo
class CoolWidgetReplicator <Gitlab::Geo::Replicator
- [ ] Add this replicator class to the method `replicator_classes` in
`ee/lib/gitlab/geo.rb`:
```ruby
REPLICATOR_CLASSES = [
::Geo::PackageFileReplicator,
::Geo::CoolWidgetReplicator
]
end
```
- [ ] Create `ee/spec/replicators/geo/cool_widget_replicator_spec.rb` and perform the necessary setup to define the `model_record` variable for the shared examples:
- [ ] Make sure the factory also allows setting a `project` attribute. If the model does not have a direct relation to a project, you can use a `transient` attribute. Check out `spec/factories/merge_request_diffs.rb` for an example.
- [ ] Following [the example of Merge Request Diffs](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/63309) add a `Geo::CoolWidgetState` model in `ee/app/models/ee/geo/cool_widget_state.rb`:
- [ ] Add integration tests for providing CoolWidget registry data to the frontend via the GraphQL API, by duplicating and modifying the following shared examples in `ee/spec/requests/api/graphql/geo/registries_spec.rb`:
```ruby
it_behaves_like 'gets registries for', {
field_name: 'coolWidgetRegistries',
registry_class_name: 'CoolWidgetRegistry',
registry_factory: :geo_cool_widget_registry,
registry_foreign_key_field_name: 'coolWidgetId'
}
```
- [ ] Update the GraphQL reference documentation:
```shell
bundle exec rake gitlab:graphql:compile_docs
```
Individual Cool Widget replication and verification data should now be available via the GraphQL API.
If batch destroy logic is implemented for a replicable, then that logic must be "replicated" by Geo secondaries. The easiest way to do this is use `Geo::BatchEventCreateWorker` to bulk insert a delete event for each replicable.
For example, if `FastDestroyAll` is used, then you may be able to [use `begin_fast_destroy` and `finalize_fast_destroy` hooks, like we did for uploads](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/69763).
Or if a special service is used to batch delete records and their associated data, then you probably need to [hook into that service, like we did for job artifacts](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/79530).
As illustrated by the above two examples, batch destroy logic cannot be handled automatically by Geo secondaries without restricting the way other teams perform batch destroys. It is up to you to produce `Geo::BatchEventCreateWorker` attributes before the records are deleted, and then enqueue `Geo::BatchEventCreateWorker` after the records are deleted.
- [ ] Ensure that any batch destroy of this replicable is replicated to secondary sites
- [ ] Regardless of implementation details, please verify in specs that when the parent object is removed, the new `Geo::Event` records are created:
- [ ] In the rollout issue you created when creating the feature flag, modify the Roll Out Steps:
- [ ] Cross out any steps related to testing on production GitLab.com, because Geo is not running on production GitLab.com at the moment.
- [ ] Add a step to `Test replication and verification of Cool Widgets on a non-GDK-deployment. For example, using GitLab Environment Toolkit`.
- [ ] Add a step to `Ping the Geo PM and EM to coordinate testing`. For example, you might add steps to generate Cool Widgets, and then a Geo engineer may take it from there.
- [ ] In `ee/config/feature_flags/development/geo_cool_widget_replication.yml`, set `default_enabled: true`
- [ ] In `ee/app/graphql/types/geo/geo_node_type.rb`, remove the `feature_flag` option for the released type:
```ruby
field :cool_widget_registries, ::Types::Geo::CoolWidgetRegistryType.connection_type,
- [ ] Add a row for Cool Widgets to the `Data types` table in [Geo data types support](https://gitlab.com/gitlab-org/gitlab/blob/master/doc/administration/geo/replication/datatypes.md#data-types)
- [ ] Add a row for Cool Widgets to the `Limitations on replication/verification` table in [Geo data types support](https://gitlab.com/gitlab-org/gitlab/blob/master/doc/administration/geo/replication/datatypes.md#limitations-on-replicationverification). If the row already exists, then update it to show that Replication and Verification is released in the current version.