Add /-/readiness /-/liveness and /-/health_metrics endpoints to track application readiness

17 files changed, 662 insertions, 20 deletions

diff --git a/app/controllers/concerns/requires_health_token.rb b/app/controllers/concerns/requires_health_token.rb
new file mode 100644
index 00000000000..34ab1a97649
--- /dev/null
+++ b/app/controllers/concerns/requires_health_token.rb
@@ -0,0 +1,25 @@
+module RequiresHealthToken
+  extend ActiveSupport::Concern
+  included do
+    before_action :validate_health_check_access!
+  end
+
+  private
+
+  def validate_health_check_access!
+    render_404 unless token_valid?
+  end
+
+  def token_valid?
+    token = params[:token].presence || request.headers['TOKEN']
+    token.present? &&
+      ActiveSupport::SecurityUtils.variable_size_secure_compare(
+        token,
+        current_application_settings.health_check_access_token
+      )
+  end
+
+  def render_404
+    render file: Rails.root.join('public', '404'), layout: false, status: '404'
+  end
+end
diff --git a/app/controllers/health_check_controller.rb b/app/controllers/health_check_controller.rb
index 037da7d2bce..5d3109b7187 100644
--- a/app/controllers/health_check_controller.rb
+++ b/app/controllers/health_check_controller.rb
@@ -1,22 +1,3 @@
 class HealthCheckController < HealthCheck::HealthCheckController
-  before_action :validate_health_check_access!
-
-  private
-
-  def validate_health_check_access!
-    render_404 unless token_valid?
-  end
-
-  def token_valid?
-    token = params[:token].presence || request.headers['TOKEN']
-    token.present? &&
-      ActiveSupport::SecurityUtils.variable_size_secure_compare(
-        token,
-        current_application_settings.health_check_access_token
-      )
-  end
-
-  def render_404
-    render file: Rails.root.join('public', '404'), layout: false, status: '404'
-  end
+  include RequiresHealthToken
 end
diff --git a/app/controllers/health_controller.rb b/app/controllers/health_controller.rb
new file mode 100644
index 00000000000..df0fc3132ed
--- /dev/null
+++ b/app/controllers/health_controller.rb
@@ -0,0 +1,60 @@
+class HealthController < ActionController::Base
+  protect_from_forgery with: :exception
+  include RequiresHealthToken
+
+  CHECKS = [
+    Gitlab::HealthChecks::DbCheck,
+    Gitlab::HealthChecks::RedisCheck,
+    Gitlab::HealthChecks::FsShardsCheck,
+  ].freeze
+
+  def readiness
+    results = CHECKS.map { |check| [check.name, check.readiness] }
+
+    render_check_results(results)
+  end
+
+  def liveness
+    results = CHECKS.map { |check| [check.name, check.liveness] }
+
+    render_check_results(results)
+  end
+
+  def metrics
+    results = CHECKS.flat_map(&:metrics)
+
+    response = results.map(&method(:metric_to_prom_line)).join("\n")
+
+    render text: response, content_type: 'text/plain; version=0.0.4'
+  end
+
+  private
+
+  def metric_to_prom_line(metric)
+    labels = metric.labels&.map { |key, value| "#{key}=\"#{value}\"" }&.join(',') || ''
+    if labels.empty?
+      "#{metric.name} #{metric.value}"
+    else
+      "#{metric.name}{#{labels}} #{metric.value}"
+    end
+  end
+
+  def render_check_results(results)
+    flattened = results.flat_map do |name, result|
+      if result.is_a?(Gitlab::HealthChecks::Result)
+        [[name, result]]
+      else
+        result.map { |r| [name, r] }
+      end
+    end
+    success = flattened.all? { |name, r| r.success }
+
+    response = flattened.map do |name, r|
+      info = { status: r.success ? 'ok' : 'failed' }
+      info['message'] = r.message if r.message
+      info[:labels] = r.labels if r.labels
+      [name, info]
+    end
+    render json: response.to_h, status: success ? :ok : :service_unavailable
+  end
+end
diff --git a/changelogs/unreleased/24240-add-monitoring-endpoints.yml b/changelogs/unreleased/24240-add-monitoring-endpoints.yml
new file mode 100644
index 00000000000..a22458965fc
--- /dev/null
+++ b/changelogs/unreleased/24240-add-monitoring-endpoints.yml
@@ -0,0 +1,4 @@
+---
+title: Add /-/readiness /-/liveness and /-/metrics endpoints to track application health
+merge_request: 10416
+author:
diff --git a/config/routes.rb b/config/routes.rb
index 1a851da6203..1da226a3b57 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -39,6 +39,12 @@ Rails.application.routes.draw do
   # Health check
   get 'health_check(/:checks)' => 'health_check#index', as: :health_check
 
+  scope path: '-', controller: 'health' do
+    get :liveness
+    get :readiness
+    get :metrics
+  end
+
   # Koding route
   get 'koding' => 'koding#index'
 
diff --git a/lib/gitlab/health_checks/base_abstract_check.rb b/lib/gitlab/health_checks/base_abstract_check.rb
new file mode 100644
index 00000000000..7de6d4d9367
--- /dev/null
+++ b/lib/gitlab/health_checks/base_abstract_check.rb
@@ -0,0 +1,45 @@
+module Gitlab
+  module HealthChecks
+    module BaseAbstractCheck
+      def name
+        super.demodulize.underscore
+      end
+
+      def human_name
+        name.sub(/_check$/, '').capitalize
+      end
+
+      def readiness
+        raise NotImplementedError
+      end
+
+      def liveness
+        HealthChecks::Result.new(true)
+      end
+
+      def metrics
+        []
+      end
+
+      protected
+
+      def metric(name, value, **labels)
+        Metric.new(name, value, labels)
+      end
+
+      def with_timing(proc)
+        start = Time.now
+        result = proc.call
+        yield result, Time.now.to_f - start.to_f
+      end
+
+      def catch_timeout(seconds, &block)
+        begin
+          Timeout.timeout(seconds.to_i, &block)
+        rescue Timeout::Error => ex
+          ex
+        end
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/health_checks/db_check.rb b/lib/gitlab/health_checks/db_check.rb
new file mode 100644
index 00000000000..fd94984f8a2
--- /dev/null
+++ b/lib/gitlab/health_checks/db_check.rb
@@ -0,0 +1,29 @@
+module Gitlab
+  module HealthChecks
+    class DbCheck
+      extend SimpleAbstractCheck
+
+      class << self
+        private
+
+        def metric_prefix
+          'db_ping'
+        end
+
+        def is_successful?(result)
+          result == '1'
+        end
+
+        def check
+          catch_timeout 10.seconds do
+            if Gitlab::Database.postgresql?
+              ActiveRecord::Base.connection.execute('SELECT 1 as ping')&.first&.[]('ping')
+            else
+              ActiveRecord::Base.connection.execute('SELECT 1 as ping')&.first&.first&.to_s
+            end
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/health_checks/fs_shards_check.rb b/lib/gitlab/health_checks/fs_shards_check.rb
new file mode 100644
index 00000000000..df962d203b7
--- /dev/null
+++ b/lib/gitlab/health_checks/fs_shards_check.rb
@@ -0,0 +1,117 @@
+module Gitlab
+  module HealthChecks
+    class FsShardsCheck
+      extend BaseAbstractCheck
+
+      class << self
+        def readiness
+          repository_storages.map do |storage_name|
+            begin
+              tmp_file_path = tmp_file_path(storage_name)
+
+              if !storage_stat_test(storage_name)
+                HealthChecks::Result.new(false, 'cannot stat storage', shard: storage_name)
+              elsif !storage_write_test(tmp_file_path)
+                HealthChecks::Result.new(false, 'cannot write to storage', shard: storage_name)
+              elsif !storage_read_test(tmp_file_path)
+                HealthChecks::Result.new(false, 'cannot read from storage', shard: storage_name)
+              else
+                HealthChecks::Result.new(true, nil, shard: storage_name)
+              end
+            rescue RuntimeError => ex
+              message = "unexpected error #{ex} when checking storage #{storage_name}"
+              Rails.logger.error(message)
+              HealthChecks::Result.new(false, message, shard: storage_name)
+            ensure
+              delete_test_file(tmp_file_path)
+            end
+          end
+        end
+
+        def metrics
+          repository_storages.flat_map do |storage_name|
+            tmp_file_path = tmp_file_path(storage_name)
+            [
+              operation_metrics(:filesystem_accessible, :filesystem_access_latency, -> { storage_stat_test(storage_name) }, shard: storage_name),
+              operation_metrics(:filesystem_writable, :filesystem_write_latency, -> { storage_write_test(tmp_file_path) }, shard: storage_name),
+              operation_metrics(:filesystem_readable, :filesystem_read_latency, -> { storage_read_test(tmp_file_path) }, shard: storage_name)
+            ].flatten
+          end
+        end
+
+        private
+
+        RANDOM_STRING = SecureRandom.hex(1000).freeze
+
+        def operation_metrics(ok_metric, latency_metric, operation, **labels)
+          with_timing operation do |result, elapsed|
+            [
+              metric(latency_metric, elapsed, **labels),
+              metric(ok_metric, result ? 1 : 0, **labels)
+            ]
+          end
+        rescue RuntimeError => ex
+          Rails.logger("unexpected error #{ex} when checking #{ok_metric}")
+          [metric(ok_metric, 0, **labels)]
+        end
+
+        def repository_storages
+          @repository_storage ||= Gitlab::CurrentSettings.current_application_settings.repository_storages
+        end
+
+        def storages_paths
+          @storage_paths ||= Gitlab.config.repositories.storages
+        end
+
+        def with_timeout(args)
+          %w{timeout 1}.concat(args)
+        end
+
+        def tmp_file_path(storage_name)
+          Dir::Tmpname.create(%w(fs_shards_check +deleted), path(storage_name)) { |path| path }
+        end
+
+        def path(storage_name)
+          storages_paths&.dig(storage_name, 'path')
+        end
+
+        def storage_stat_test(storage_name)
+          stat_path = File.join(path(storage_name), '.')
+          begin
+            _, status = Gitlab::Popen.popen(with_timeout(%W{ stat #{stat_path} }))
+            status == 0
+          rescue Errno::ENOENT
+            File.exist?(stat_path) && File::Stat.new(stat_path).readable?
+          end
+        end
+
+        def storage_write_test(tmp_path)
+          _, status = Gitlab::Popen.popen(with_timeout(%W{ tee #{tmp_path} })) do |stdin|
+            stdin.write(RANDOM_STRING)
+          end
+          status == 0
+        rescue Errno::ENOENT
+          written_bytes = File.write(tmp_path, RANDOM_STRING) rescue Errno::ENOENT
+          written_bytes == RANDOM_STRING.length
+        end
+
+        def storage_read_test(tmp_path)
+          _, status = Gitlab::Popen.popen(with_timeout(%W{ diff #{tmp_path} - })) do |stdin|
+            stdin.write(RANDOM_STRING)
+          end
+          status == 0
+        rescue Errno::ENOENT
+          file_contents = File.read(tmp_path) rescue Errno::ENOENT
+          file_contents == RANDOM_STRING
+        end
+
+        def delete_test_file(tmp_path)
+          _, status = Gitlab::Popen.popen(with_timeout(%W{ rm -f #{tmp_path} }))
+          status == 0
+        rescue Errno::ENOENT
+          File.delete(tmp_path) rescue Errno::ENOENT
+        end
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/health_checks/metric.rb b/lib/gitlab/health_checks/metric.rb
new file mode 100644
index 00000000000..1a2eab0b005
--- /dev/null
+++ b/lib/gitlab/health_checks/metric.rb
@@ -0,0 +1,3 @@
+module Gitlab::HealthChecks
+  Metric = Struct.new(:name, :value, :labels)
+end
diff --git a/lib/gitlab/health_checks/redis_check.rb b/lib/gitlab/health_checks/redis_check.rb
new file mode 100644
index 00000000000..57bbe5b3ad0
--- /dev/null
+++ b/lib/gitlab/health_checks/redis_check.rb
@@ -0,0 +1,25 @@
+module Gitlab
+  module HealthChecks
+    class RedisCheck
+      extend SimpleAbstractCheck
+
+      class << self
+        private
+
+        def metric_prefix
+          'redis_ping'
+        end
+
+        def is_successful?(result)
+          result == 'PONG'
+        end
+
+        def check
+          catch_timeout 10.seconds do
+            Gitlab::Redis.with(&:ping)
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/health_checks/result.rb b/lib/gitlab/health_checks/result.rb
new file mode 100644
index 00000000000..8086760023e
--- /dev/null
+++ b/lib/gitlab/health_checks/result.rb
@@ -0,0 +1,3 @@
+module Gitlab::HealthChecks
+  Result = Struct.new(:success, :message, :labels)
+end
diff --git a/lib/gitlab/health_checks/simple_abstract_check.rb b/lib/gitlab/health_checks/simple_abstract_check.rb
new file mode 100644
index 00000000000..fbe1645c1b1
--- /dev/null
+++ b/lib/gitlab/health_checks/simple_abstract_check.rb
@@ -0,0 +1,43 @@
+module Gitlab
+  module HealthChecks
+    module SimpleAbstractCheck
+      include BaseAbstractCheck
+
+      def readiness
+        check_result = check
+        if is_successful?(check_result)
+          HealthChecks::Result.new(true)
+        elsif check_result.is_a?(Timeout::Error)
+          HealthChecks::Result.new(false, "#{human_name} check timed out")
+        else
+          HealthChecks::Result.new(false, "unexpected #{human_name} check result: #{check_result}")
+        end
+      end
+
+      def metrics
+        with_timing method(:check) do |result, elapsed|
+          Rails.logger.error("#{human_name} check returned unexpected result #{result}") unless is_successful?(result)
+          [
+            metric("#{metric_prefix}_timeout", result.is_a?(Timeout::Error) ? 1 : 0),
+            metric("#{metric_prefix}_success", is_successful?(result) ? 1 : 0),
+            metric("#{metric_prefix}_latency", elapsed)
+          ]
+        end
+      end
+
+      private
+
+      def metric_prefix
+        raise NotImplementedError
+      end
+
+      def is_successful?(result)
+        raise NotImplementedError
+      end
+
+      def check
+        raise NotImplementedError
+      end
+    end
+  end
+end
diff --git a/spec/controllers/health_controller_spec.rb b/spec/controllers/health_controller_spec.rb
new file mode 100644
index 00000000000..b8b6e0c3a88
--- /dev/null
+++ b/spec/controllers/health_controller_spec.rb
@@ -0,0 +1,96 @@
+require 'spec_helper'
+
+describe HealthController do
+  include StubENV
+
+  let(:token) { current_application_settings.health_check_access_token }
+  let(:json_response) { JSON.parse(response.body) }
+
+  before do
+    stub_env('IN_MEMORY_APPLICATION_SETTINGS', 'false')
+  end
+
+  describe '#readiness' do
+    context 'authorization token provided' do
+      before do
+        request.headers['TOKEN'] = token
+      end
+
+      it 'returns proper response' do
+        get :readiness
+        expect(json_response['db_check']['status']).to eq('ok')
+        expect(json_response['redis_check']['status']).to eq('ok')
+        expect(json_response['fs_shards_check']['status']).to eq('ok')
+        expect(json_response['fs_shards_check']['labels']['shard']).to eq('default')
+      end
+    end
+
+    context 'without authorization token' do
+      it 'returns proper response' do
+        get :readiness
+        expect(response.status).to eq(404)
+      end
+    end
+  end
+
+  describe '#liveness' do
+    context 'authorization token provided' do
+      before do
+        request.headers['TOKEN'] = token
+      end
+
+      it 'returns proper response' do
+        get :liveness
+        expect(json_response['db_check']['status']).to eq('ok')
+        expect(json_response['redis_check']['status']).to eq('ok')
+        expect(json_response['fs_shards_check']['status']).to eq('ok')
+      end
+    end
+
+    context 'without authorization token' do
+      it 'returns proper response' do
+        get :liveness
+        expect(response.status).to eq(404)
+      end
+    end
+  end
+
+  describe '#metrics' do
+    context 'authorization token provided' do
+      before do
+        request.headers['TOKEN'] = token
+      end
+
+      it 'returns DB ping metrics' do
+        get :metrics
+        expect(response.body).to match(/^db_ping_timeout 0$/)
+        expect(response.body).to match(/^db_ping_success 1$/)
+        expect(response.body).to match(/^db_ping_latency [0-9\.]+$/)
+      end
+
+      it 'returns Redis ping metrics' do
+        get :metrics
+        expect(response.body).to match(/^redis_ping_timeout 0$/)
+        expect(response.body).to match(/^redis_ping_success 1$/)
+        expect(response.body).to match(/^redis_ping_latency [0-9\.]+$/)
+      end
+
+      it 'returns file system check metrics' do
+        get :metrics
+        expect(response.body).to match(/^filesystem_access_latency{shard="default"} [0-9\.]+$/)
+        expect(response.body).to match(/^filesystem_accessible{shard="default"} 1$/)
+        expect(response.body).to match(/^filesystem_write_latency{shard="default"} [0-9\.]+$/)
+        expect(response.body).to match(/^filesystem_writable{shard="default"} 1$/)
+        expect(response.body).to match(/^filesystem_read_latency{shard="default"} [0-9\.]+$/)
+        expect(response.body).to match(/^filesystem_readable{shard="default"} 1$/)
+      end
+    end
+
+    context 'without authorization token' do
+      it 'returns proper response' do
+        get :metrics
+        expect(response.status).to eq(404)
+      end
+    end
+  end
+end
diff --git a/spec/lib/gitlab/healthchecks/db_check_spec.rb b/spec/lib/gitlab/healthchecks/db_check_spec.rb
new file mode 100644
index 00000000000..33c6c24449c
--- /dev/null
+++ b/spec/lib/gitlab/healthchecks/db_check_spec.rb
@@ -0,0 +1,6 @@
+require 'spec_helper'
+require_relative './simple_check_shared'
+
+describe Gitlab::HealthChecks::DbCheck do
+  include_examples 'simple_check', 'db_ping', 'Db', '1'
+end
diff --git a/spec/lib/gitlab/healthchecks/fs_shards_check_spec.rb b/spec/lib/gitlab/healthchecks/fs_shards_check_spec.rb
new file mode 100644
index 00000000000..4cd8cf313a5
--- /dev/null
+++ b/spec/lib/gitlab/healthchecks/fs_shards_check_spec.rb
@@ -0,0 +1,127 @@
+require 'spec_helper'
+
+describe Gitlab::HealthChecks::FsShardsCheck do
+  let(:metric_class) { Gitlab::HealthChecks::Metric }
+  let(:result_class) { Gitlab::HealthChecks::Result }
+  let(:repository_storages) { [:default] }
+  let(:tmp_dir) { Dir.mktmpdir }
+
+  let(:storages_paths) do
+    {
+      default: { path: tmp_dir }
+    }.with_indifferent_access
+  end
+
+  before do
+    allow(described_class).to receive(:repository_storages) { repository_storages }
+    allow(described_class).to receive(:storages_paths) { storages_paths }
+  end
+
+  after do
+    FileUtils.remove_entry_secure(tmp_dir) if Dir.exist?(tmp_dir)
+  end
+
+  shared_examples 'filesystem checks' do
+    describe '#readiness' do
+      subject { described_class.readiness }
+
+      context 'storage points to not existing folder' do
+        let(:storages_paths) do
+          {
+            default: { path: 'tmp/this/path/doesnt/exist' }
+          }.with_indifferent_access
+        end
+
+        it { is_expected.to include(result_class.new(false, 'cannot stat storage', shard: :default)) }
+      end
+
+      context 'storage points to directory that has both read and write rights' do
+        before do
+          FileUtils.chmod_R(0755, tmp_dir)
+        end
+
+        it { is_expected.to include(result_class.new(true, nil, shard: :default)) }
+
+        it 'cleans up files used for testing' do
+          expect(described_class).to receive(:storage_write_test).with(any_args).and_call_original
+
+          subject
+
+          expect(Dir.entries(tmp_dir).count).to eq(2)
+        end
+
+        context 'read test fails' do
+          before do
+            allow(described_class).to receive(:storage_read_test).with(any_args).and_return(false)
+          end
+
+          it { is_expected.to include(result_class.new(false, 'cannot read from storage', shard: :default)) }
+        end
+
+        context 'write test fails' do
+          before do
+            allow(described_class).to receive(:storage_write_test).with(any_args).and_return(false)
+          end
+
+          it { is_expected.to include(result_class.new(false, 'cannot write to storage', shard: :default)) }
+        end
+      end
+    end
+
+    describe '#metrics' do
+      subject { described_class.metrics }
+
+      context 'storage points to not existing folder' do
+        let(:storages_paths) do
+          {
+            default: { path: 'tmp/this/path/doesnt/exist' }
+          }.with_indifferent_access
+        end
+
+        it { is_expected.to include(metric_class.new(:filesystem_accessible, 0, shard: :default)) }
+        it { is_expected.to include(metric_class.new(:filesystem_readable, 0, shard: :default)) }
+        it { is_expected.to include(metric_class.new(:filesystem_writable, 0, shard: :default)) }
+
+        it { is_expected.to include(have_attributes(name: :filesystem_access_latency, value: be > 0, labels: { shard: :default })) }
+        it { is_expected.to include(have_attributes(name: :filesystem_read_latency, value: be > 0, labels: { shard: :default })) }
+        it { is_expected.to include(have_attributes(name: :filesystem_write_latency, value: be > 0, labels: { shard: :default })) }
+      end
+
+      context 'storage points to directory that has both read and write rights' do
+        before do
+          FileUtils.chmod_R(0755, tmp_dir)
+        end
+
+        it { is_expected.to include(metric_class.new(:filesystem_accessible, 1, shard: :default)) }
+        it { is_expected.to include(metric_class.new(:filesystem_readable, 1, shard: :default)) }
+        it { is_expected.to include(metric_class.new(:filesystem_writable, 1, shard: :default)) }
+
+        it { is_expected.to include(have_attributes(name: :filesystem_access_latency, value: be > 0, labels: { shard: :default })) }
+        it { is_expected.to include(have_attributes(name: :filesystem_read_latency, value: be > 0, labels: { shard: :default })) }
+        it { is_expected.to include(have_attributes(name: :filesystem_write_latency, value: be > 0, labels: { shard: :default })) }
+      end
+    end
+  end
+
+  context 'when popen always finds required binaries' do
+    before do
+      allow(Gitlab::Popen).to receive(:popen).and_wrap_original do |method, *args, &block|
+        begin
+          method.call(*args, &block)
+        rescue RuntimeError
+          raise 'expected not to happen'
+        end
+      end
+    end
+
+    it_behaves_like 'filesystem checks'
+  end
+
+  context 'when popen never finds required binaries' do
+    before do
+      allow(Gitlab::Popen).to receive(:popen).and_raise(Errno::ENOENT)
+    end
+
+    it_behaves_like 'filesystem checks'
+  end
+end
diff --git a/spec/lib/gitlab/healthchecks/redis_check_spec.rb b/spec/lib/gitlab/healthchecks/redis_check_spec.rb
new file mode 100644
index 00000000000..734cdcb893e
--- /dev/null
+++ b/spec/lib/gitlab/healthchecks/redis_check_spec.rb
@@ -0,0 +1,6 @@
+require 'spec_helper'
+require_relative './simple_check_shared'
+
+describe Gitlab::HealthChecks::RedisCheck do
+  include_examples 'simple_check', 'redis_ping', 'Redis', 'PONG'
+end
diff --git a/spec/lib/gitlab/healthchecks/simple_check_shared.rb b/spec/lib/gitlab/healthchecks/simple_check_shared.rb
new file mode 100644
index 00000000000..1fa6d0faef9
--- /dev/null
+++ b/spec/lib/gitlab/healthchecks/simple_check_shared.rb
@@ -0,0 +1,66 @@
+shared_context 'simple_check' do |metrics_prefix, check_name, success_result|
+  describe '#metrics' do
+    subject { described_class.metrics }
+    context 'Check is passing' do
+      before do
+        allow(described_class).to receive(:check).and_return success_result
+      end
+
+      it { is_expected.to include(have_attributes(name: "#{metrics_prefix}_success", value: 1)) }
+      it { is_expected.to include(have_attributes(name: "#{metrics_prefix}_timeout", value: 0)) }
+      it { is_expected.to include(have_attributes(name: "#{metrics_prefix}_latency", value: be > 0)) }
+    end
+
+    context 'Check is misbehaving' do
+      before do
+        allow(described_class).to receive(:check).and_return 'error!'
+      end
+
+      it { is_expected.to include(have_attributes(name: "#{metrics_prefix}_success", value: 0)) }
+      it { is_expected.to include(have_attributes(name: "#{metrics_prefix}_timeout", value: 0)) }
+      it { is_expected.to include(have_attributes(name: "#{metrics_prefix}_latency", value: be > 0)) }
+    end
+
+    context 'Check is timeouting' do
+      before do
+        allow(described_class).to receive(:check).and_return Timeout::Error.new
+      end
+
+      it { is_expected.to include(have_attributes(name: "#{metrics_prefix}_success", value: 0)) }
+      it { is_expected.to include(have_attributes(name: "#{metrics_prefix}_timeout", value: 1)) }
+      it { is_expected.to include(have_attributes(name: "#{metrics_prefix}_latency", value: be > 0)) }
+    end
+  end
+
+  describe '#readiness' do
+    subject { described_class.readiness }
+    context 'Check returns ok' do
+      before do
+        allow(described_class).to receive(:check).and_return success_result
+      end
+
+      it { is_expected.to have_attributes(success: true) }
+    end
+
+    context 'Check is misbehaving' do
+      before do
+        allow(described_class).to receive(:check).and_return 'error!'
+      end
+
+      it { is_expected.to have_attributes(success: false, message: "unexpected #{check_name} check result: error!") }
+    end
+
+    context 'Check is timeouting' do
+      before do
+        allow(described_class).to receive(:check ).and_return Timeout::Error.new
+      end
+
+      it { is_expected.to have_attributes(success: false, message: "#{check_name} check timed out") }
+    end
+  end
+
+  describe '#liveness' do
+    subject { described_class.readiness }
+    it { is_expected.to eq(Gitlab::HealthChecks::Result.new(true)) }
+  end
+end