--- stage: Systems group: Gitaly info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments --- # Gitaly developers guide [Gitaly](https://gitlab.com/gitlab-org/gitaly) is a high-level Git RPC service used by GitLab Rails, Workhorse and GitLab Shell. ## Deep Dive In May 2019, Bob Van Landuyt hosted a Deep Dive (GitLab team members only: `https://gitlab.com/gitlab-org/create-stage/issues/1`) on the [Gitaly project](https://gitlab.com/gitlab-org/gitaly). It included how to contribute to it as a Ruby developer, and shared domain-specific knowledge with anyone who may work in this part of the codebase in the future. You can find the [recording on YouTube](https://www.youtube.com/watch?v=BmlEWFS8ORo), and the slides on [Google Slides](https://docs.google.com/presentation/d/1VgRbiYih9ODhcPnL8dS0W98EwFYpJ7GXMPpX-1TM6YE/edit) and in [PDF](https://gitlab.com/gitlab-org/create-stage/uploads/a4fdb1026278bda5c1c5bb574379cf80/Create_Deep_Dive__Gitaly_for_Create_Ruby_Devs.pdf). Everything covered in this deep dive was accurate as of GitLab 11.11, and while specific details may have changed, it should still serve as a good introduction. ## Beginner's guide Start by reading the Gitaly repository's [Beginner's guide to Gitaly contributions](https://gitlab.com/gitlab-org/gitaly/-/blob/master/doc/beginners_guide.md). It describes how to set up Gitaly, the various components of Gitaly and what they do, and how to run its test suites. ## Developing new Git features To read or write Git data, a request has to be made to Gitaly. This means that if you're developing a new feature where you need data that's not yet available in `lib/gitlab/git` changes have to be made to Gitaly. There should be no new code that touches Git repositories via disk access (for example, Rugged, `git`, `rm -rf`) anywhere in the `gitlab` repository. Anything that needs direct access to the Git repository *must* be implemented in Gitaly, and exposed via an RPC. It's often easier to develop a new feature in Gitaly if you make the changes to GitLab that intends to use the new feature in a separate merge request, to be merged immediately after the Gitaly one. This allows you to test your changes before they are merged. - See [below](#running-tests-with-a-locally-modified-version-of-gitaly) for instructions on running GitLab tests with a modified version of Gitaly. - In GDK run `gdk install` and restart GDK using `gdk restart` to use a locally modified Gitaly version for development ### `gitaly-ruby` It is possible to implement and test RPC's in Gitaly using Ruby code, in [`gitaly-ruby`](https://gitlab.com/gitlab-org/gitaly/tree/master/ruby). This should make it easier to contribute for developers who are less comfortable writing Go code. For more information, see the [Beginner's guide to Gitaly contributions](https://gitlab.com/gitlab-org/gitaly/-/blob/master/doc/beginners_guide.md). ## Gitaly-Related Test Failures If your test-suite is failing with Gitaly issues, as a first step, try running: ```shell rm -rf tmp/tests/gitaly ``` During RSpec tests, the Gitaly instance writes logs to `gitlab/log/gitaly-test.log`. ## Legacy Rugged code While Gitaly can handle all Git access, many of GitLab customers still run Gitaly atop NFS. The legacy Rugged implementation for Git calls may be faster than the Gitaly RPC due to N+1 Gitaly calls and other reasons. See [the issue](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/57317) for more details. Until GitLab has eliminated most of these inefficiencies or the use of NFS is discontinued for Git data, Rugged implementations of some of the most commonly-used RPCs can be enabled via feature flags: - `rugged_find_commit` - `rugged_get_tree_entries` - `rugged_tree_entry` - `rugged_commit_is_ancestor` - `rugged_commit_tree_entry` - `rugged_list_commits_by_oid` A convenience Rake task can be used to enable or disable these flags all together. To enable: ```shell bundle exec rake gitlab:features:enable_rugged ``` To disable: ```shell bundle exec rake gitlab:features:disable_rugged ``` Most of this code exists in the `lib/gitlab/git/rugged_impl` directory. NOTE: You should *not* have to add or modify code related to Rugged unless explicitly discussed with the [Gitaly Team](https://gitlab.com/groups/gl-gitaly/group_members). This code does not work on GitLab.com or other GitLab instances that do not use NFS. ## `TooManyInvocationsError` errors During development and testing, you may experience `Gitlab::GitalyClient::TooManyInvocationsError` failures. The `GitalyClient` attempts to block against potential n+1 issues by raising this error when Gitaly is called more than 30 times in a single Rails request or Sidekiq execution. As a temporary measure, export `GITALY_DISABLE_REQUEST_LIMITS=1` to suppress the error. This disables the n+1 detection in your development environment. Please raise an issue in the GitLab CE or EE repositories to report the issue. Include the labels ~Gitaly ~performance ~"technical debt". Please ensure that the issue contains the full stack trace and error message of the `TooManyInvocationsError`. Also include any known failing tests if possible. Isolate the source of the n+1 problem. This is normally a loop that results in Gitaly being called for each element in an array. If you are unable to isolate the problem, please contact a member of the [Gitaly Team](https://gitlab.com/groups/gl-gitaly/group_members) for assistance. After the source has been found, wrap it in an `allow_n_plus_1_calls` block, as follows: ```ruby # n+1: link to n+1 issue Gitlab::GitalyClient.allow_n_plus_1_calls do # original code commits.each { |commit| ... } end ``` After the code is wrapped in this block, this code path is excluded from n+1 detection. ## Request counts Commits and other Git data, is now fetched through Gitaly. These fetches can, much like with a database, be batched. This improves performance for the client and for Gitaly itself and therefore for the users too. To keep performance stable and guard performance regressions, Gitaly calls can be counted and the call count can be tested against. This requires the `:request_store` flag to be set. ```ruby describe 'Gitaly Request count tests' do context 'when the request store is activated', :request_store do it 'correctly counts the gitaly requests made' do expect { subject }.to change { Gitlab::GitalyClient.get_request_count }.by(10) end end end ``` ## Running tests with a locally modified version of Gitaly Normally, GitLab CE/EE tests use a local clone of Gitaly in `tmp/tests/gitaly` pinned at the version specified in `GITALY_SERVER_VERSION`. The `GITALY_SERVER_VERSION` file supports also branches and SHA to use a custom commit in [the repository](https://gitlab.com/gitlab-org/gitaly). NOTE: With the introduction of auto-deploy for Gitaly, the format of `GITALY_SERVER_VERSION` was aligned with Omnibus syntax. It no longer supports `=revision`, it evaluates the file content as a Git reference (branch or SHA). Only if it matches a semantic version does it prepend a `v`. If you want to run tests locally against a modified version of Gitaly you can replace `tmp/tests/gitaly` with a symlink. This is much faster because it avoids a Gitaly re-install each time you run `rspec`. Make sure this directory contains the files `config.toml` and `praefect.config.toml`. You can copy them from `config.toml.example` and `config.praefect.toml.example` respectively. After copying, make sure to edit them so everything points to the correct paths. ```shell rm -rf tmp/tests/gitaly ln -s /path/to/gitaly tmp/tests/gitaly ``` Make sure you run `make` in your local Gitaly directory before running tests. Otherwise, Gitaly fails to boot. If you make changes to your local Gitaly in between test runs you need to manually run `make` again. Note that CI tests do not use your locally modified version of Gitaly. To use a custom Gitaly version in CI, you must update GITALY_SERVER_VERSION as described at the beginning of this section. To use a different Gitaly repository, such as if your changes are present on a fork, you can specify a `GITALY_REPO_URL` environment variable when running tests: ```shell GITALY_REPO_URL=https://gitlab.com/nick.thomas/gitaly bundle exec rspec spec/lib/gitlab/git/repository_spec.rb ``` If your fork of Gitaly is private, you can generate a [Deploy Token](../user/project/deploy_tokens/index.md) and specify it in the URL: ```shell GITALY_REPO_URL=https://gitlab+deploy-token-1000:token-here@gitlab.com/nick.thomas/gitaly bundle exec rspec spec/lib/gitlab/git/repository_spec.rb ``` To use a custom Gitaly repository in CI/CD, for instance if you want your GitLab fork to always use your own Gitaly fork, set `GITALY_REPO_URL` as a [CI/CD variable](../ci/variables/index.md). ### Use a locally modified version of Gitaly RPC client If you are making changes to the RPC client, such as adding a new endpoint or adding a new parameter to an existing endpoint, follow the guide for [Gitaly protobuf specifications](https://gitlab.com/gitlab-org/gitaly/blob/master/proto/README.md). After pushing the branch with the changes (`new-feature-branch`, for example): 1. Change the `gitaly` line in the Rails' `Gemfile` to: ```ruby gem 'gitaly', git: 'https://gitlab.com/gitlab-org/gitaly.git', branch: 'new-feature-branch' ``` 1. Run `bundle install` to use the modified RPC client. Re-run `bundle install` in the `gitlab` project each time the Gitaly branch changes to embed a new SHA in the `Gemfile.lock` file. --- [Return to Development documentation](index.md) ## Wrapping RPCs in Feature Flags Here are the steps to gate a new feature in Gitaly behind a feature flag. ### Gitaly 1. Create a package scoped flag name: ```golang var findAllTagsFeatureFlag = "go-find-all-tags" ``` 1. Create a switch in the code using the `featureflag` package: ```golang if featureflag.IsEnabled(ctx, findAllTagsFeatureFlag) { // go implementation } else { // ruby implementation } ``` 1. Create Prometheus metrics: ```golang var findAllTagsRequests = prometheus.NewCounterVec( prometheus.CounterOpts{ Name: "gitaly_find_all_tags_requests_total", Help: "Counter of go vs ruby implementation of FindAllTags", }, []string{"implementation"}, ) func init() { prometheus.Register(findAllTagsRequests) } if featureflag.IsEnabled(ctx, findAllTagsFeatureFlag) { findAllTagsRequests.WithLabelValues("go").Inc() // go implementation } else { findAllTagsRequests.WithLabelValues("ruby").Inc() // ruby implementation } ``` 1. Set headers in tests: ```golang import ( "google.golang.org/grpc/metadata" "gitlab.com/gitlab-org/gitaly/internal/featureflag" ) //... md := metadata.New(map[string]string{featureflag.HeaderKey(findAllTagsFeatureFlag): "true"}) ctx = metadata.NewOutgoingContext(context.Background(), md) c, err = client.FindAllTags(ctx, rpcRequest) require.NoError(t, err) ``` ### GitLab Rails Test in a Rails console by setting the feature flag: ```ruby Feature.enable('gitaly_go_find_all_tags') ``` Pay attention to the name of the flag and the one used in the Rails console. There is a difference between them (dashes replaced by underscores and name prefix is changed). Make sure to prefix all flags with `gitaly_`. NOTE: If not set in GitLab, feature flags are read as false from the console and Gitaly uses their default value. The default value depends on the GitLab version. ### Testing with GDK To be sure that the flag is set correctly and it goes into Gitaly, you can check the integration by using GDK: 1. The state of the flag must be observable. To check it, you must enable it by fetching the Prometheus metrics: 1. Navigate to GDK's root directory. 1. Make sure you have the proper branch checked out for Gitaly. 1. Recompile it with `make gitaly-setup` and restart the service with `gdk restart gitaly`. 1. Make sure your setup is running: `gdk status | grep praefect`. 1. Check what configuration file is used: `cat ./services/praefect/run | grep praefect` value of the `-config` flag 1. Uncomment `prometheus_listen_addr` in the configuration file and run `gdk restart gitaly`. 1. Make sure that the flag is not enabled yet: 1. Perform whatever action is required to trigger your changes, such as project creation, submitting commit, or observing history. 1. Check that the list of current metrics has the new counter for the feature flag: ```shell curl --silent "http://localhost:9236/metrics" | grep go_find_all_tags ``` 1. After you observe the metrics for the new feature flag and it increments, you can enable the new feature: 1. Navigate to GDK's root directory. 1. Start a Rails console: ```shell bundle install && bundle exec rails console ``` 1. Check the list of feature flags: ```ruby Feature::Gitaly.server_feature_flags ``` It should be disabled `"gitaly-feature-go-find-all-tags"=>"false"`. 1. Enable it: ```ruby Feature.enable('gitaly_go_find_all_tags') ``` 1. Exit the Rails console and perform whatever action is required to trigger your changes, such as project creation, submitting commit, or observing history. 1. Verify the feature is on by observing the metrics for it: ```shell curl --silent "http://localhost:9236/metrics" | grep go_find_all_tags ``` ## Using Praefect in test By default Praefect in test uses an in-memory election strategy. This strategy is deprecated and no longer used in production. It mainly is kept for unit-testing purposes. A more modern election strategy requires a connection with a PostgreSQL database. This behavior is disabled by default when running tests, but you can enable it by setting `GITALY_PRAEFECT_WITH_DB=1` in your environment. This requires you have PostgreSQL running, and you have the database created. When you are using GDK, you can set it up with: 1. Start the database: `gdk start db` 1. Load the environment from GDK: `eval $(cd ../gitaly && gdk env)` 1. Create the database: `createdb --encoding=UTF8 --locale=C --echo praefect_test`