Add e2e test of distributed reads

doc/development/testing_guide/end_to_end/running_tests_that_require_special_setup.md

@@ -48,3 +48,89 @@ only to prevent it from running in the pipelines for live environments such as S
 
 If Jenkins Docker container exits without providing any information in the logs, try increasing the memory used by
 the Docker Engine.
+
+## Gitaly Cluster tests
+
+The tests tagged `:gitaly_ha` are orchestrated tests that can only be run against a set of Docker containers as configured and started by [the `Test::Integration::GitalyCluster` GitLab QA scenario](https://gitlab.com/gitlab-org/gitlab-qa/-/blob/master/docs/what_tests_can_be_run.md#testintegrationgitalycluster-ceeefull-image-address).
+
+As described in the documentation about the scenario noted above, the following command will run the tests:
+
+```shell
+gitlab-qa Test::Integration::GitalyCluster EE
+```
+
+However, that will remove the containers after it finishes running the tests. If you would like to do further testing, for example, if you would like to run a single test via a debugger, you can use [the `--no-tests` option](https://gitlab.com/gitlab-org/gitlab-qa#command-line-options) to make `gitlab-qa` skip running the tests, and to leave the containers running so that you can continue to use them.
+
+```shell
+gitlab-qa Test::Integration::GitalyCluster EE --no-tests
+```
+
+When all the containers are running you will see the output of the `docker ps` command, showing on which ports the GitLab container can be accessed. For example:
+
+```plaintext
+CONTAINER ID   ...     PORTS                                    NAMES
+d15d3386a0a8   ...     22/tcp, 443/tcp, 0.0.0.0:32772->80/tcp   gitlab-gitaly-ha
+```
+
+That shows that the GitLab instance running in the `gitlab-gitaly-ha` container can be reached via `http://localhost:32772`. However, Git operations like cloning and pushing are performed against the URL revealed via the UI as the clone URL. It uses the hostname configured for the GitLab instance, which in this case matches the Docker container name and network, `gitlab-gitaly-ha.test`. Before you can run the tests you need to configure your computer to access the container via that address. One option is to [use caddyserver as described for running tests against GDK](https://gitlab.com/gitlab-org/gitlab-qa/-/blob/master/docs/run_qa_against_gdk.md#workarounds).
+
+Another option is to use NGINX.
+
+In both cases you will need to configure your machine to translate `gitlab-gitlab-ha.test` into an appropriate IP address:
+
+```shell
+echo '127.0.0.1 gitlab-gitaly-ha.test' | sudo tee -a /etc/hosts
+```
+
+Then install NGINX:
+
+```shell
+# on macOS
+brew install nginx
+
+# on Debian/Ubuntu
+apt install nginx
+
+# on Fedora
+yum install nginx
+```
+
+Finally, configure NGINX to pass requests for `gitlab-gitaly-ha.test` to the GitLab instance:
+
+```plaintext
+# On Debian/Ubuntu, in /etc/nginx/sites-enabled/gitlab-cluster
+# On macOS, in /usr/local/etc/nginx/nginx.conf
+
+server {
+  server_name gitlab-gitaly-ha.test;
+  client_max_body_size 500m;
+
+  location / {
+    proxy_pass http://127.0.0.1:32772;
+    proxy_set_header Host gitlab-gitaly-ha.test;
+  }
+}
+```
+
+Restart NGINX for the configuration to take effect. For example:
+
+```shell
+# On Debian/Ubuntu
+sudo systemctl restart nginx
+
+# on macOS
+sudo nginx -s reload
+```
+
+You could then run the tests from the `/qa` directory:
+
+```shell
+CHROME_HEADLESS=false bin/qa Test::Instance::All http://gitlab-gitaly-ha.test -- --tag gitaly_ha
+```
+
+Once you have finished testing you can stop and remove the Docker containers:
+
+```shell
+docker stop gitlab-gitaly-ha praefect postgres gitaly3 gitaly2 gitaly1
+docker rm gitlab-gitaly-ha praefect postgres gitaly3 gitaly2 gitaly1
+```

qa/qa/resource/repository/commit.rb

@@ -59,14 +59,19 @@ module QA
           @update_files = files
         end
 
-        def resource_web_url(resource)
+        # If `actions` are specified, it performs the actions to create,
+        # update, or delete commits. If no actions are specified it
+        # gets existing commits.
+        def fabricate_via_api!
+          return api_get if actions.empty?
+
+          super
+        rescue ResourceNotFoundError
           super
-        rescue ResourceURLMissingError
-          # this particular resource does not expose a web_url property
         end
 
         def api_get_path
-          "#{api_post_path}/#{@sha}"
+          api_post_path
         end
 
         def api_post_path

qa/qa/service/praefect_manager.rb

@@ -7,6 +7,8 @@ module QA
 
       attr_accessor :gitlab
 
+      PrometheusQueryError = Class.new(StandardError)
+
       def initialize
         @gitlab = 'gitlab-gitaly-ha'
         @praefect = 'praefect'
@@ -106,6 +108,18 @@ module QA
         )
       end
 
+      def query_read_distribution
+        output = shell "docker exec gitlab-gitaly-ha bash -c 'curl -s http://localhost:9090/api/v1/query?query=gitaly_praefect_read_distribution'" do |line|
+          QA::Runtime::Logger.debug(line)
+          break line
+        end
+        result = JSON.parse(output)
+
+        raise PrometheusQueryError, "Unable to query read distribution metrics" unless result['status'] == 'success'
+
+        result['data']['result'].map { |result| { node: result['metric']['storage'], value: result['value'][1].to_i } }
+      end
+
       def replication_queue_lock_count
         result = []
         shell sql_to_docker_exec_cmd("select count(*) from replication_queue_lock where acquired = 't';") do |line|
@@ -285,6 +299,18 @@ module QA
         )
       end
 
+      # Waits until there is an increase in the number of reads for
+      # any node compared to the number of reads provided
+      def wait_for_read_count_change(pre_read_data)
+        diff_found = false
+        Support::Waiter.wait_until(sleep_interval: 5) do
+          query_read_distribution.each_with_index do |data, index|
+            diff_found = true if data[:value] > pre_read_data[index][:value]
+          end
+          diff_found
+        end
+      end
+
       def wait_for_reliable_connection
         QA::Runtime::Logger.info('Wait until GitLab and Praefect can communicate reliably')
         wait_for_praefect

qa/qa/specs/features/api/3_create/repository/distributed_reads_spec.rb

+# frozen_string_literal: true
+
+require 'parallel'
+
+module QA
+  RSpec.describe 'Create' do
+    context 'Gitaly' do
+      # Issue to track removal of feature flag: https://gitlab.com/gitlab-org/quality/team-tasks/-/issues/602
+      describe 'Distributed reads', :orchestrated, :gitaly_ha, :skip_live_env, :requires_admin do
+        let(:number_of_reads) { 100 }
+        let(:praefect_manager) { Service::PraefectManager.new }
+        let(:project) do
+          Resource::Project.fabricate! do |project|
+            project.name = "gitaly_cluster"
+            project.initialize_with_readme = true
+          end
+        end
+
+        before do
+          Runtime::Feature.enable_and_verify('gitaly_distributed_reads')
+          praefect_manager.wait_for_replication(project.id)
+        end
+
+        after do
+          Runtime::Feature.disable_and_verify('gitaly_distributed_reads')
+        end
+
+        it 'reads from each node' do
+          pre_read_data = praefect_manager.query_read_distribution
+
+          QA::Runtime::Logger.info('Fetching commits from the repository')
+          Parallel.each((1..number_of_reads)) do |index|
+            Resource::Repository::Commit.fabricate_via_api! do |commits|
+              commits.project = project
+            end
+          end
+
+          praefect_manager.wait_for_read_count_change(pre_read_data)
+
+          aggregate_failures "each gitaly node" do
+            praefect_manager.query_read_distribution.each_with_index do |data, index|
+              expect(data[:value])
+                .to be > pre_read_data[index][:value],
+                  "Read counts did not differ for node #{pre_read_data[index][:node]}"
+            end
+          end
+        end
+      end
+    end
+  end
+end