Merge branch 'bvl-circuitbreaker-backoff' into 'master'

Circuitbreaker backoff and retries

Closes #37383 and #38231

See merge request gitlab-org/gitlab-ce!14933

app/helpers/application_settings_helper.rb

@@ -120,6 +120,15 @@ module ApplicationSettingsHelper
     message.html_safe
   end
 
+  def circuitbreaker_access_retries_help_text
+    _('The number of attempts GitLab will make to access a storage.')
+  end
+
+  def circuitbreaker_backoff_threshold_help_text
+    _("The number of failures after which GitLab will start temporarily "\
+      "disabling access to a storage shard on a host")
+  end
+
   def circuitbreaker_failure_wait_time_help_text
     _("When access to a storage fails. GitLab will prevent access to the "\
       "storage for the time specified here. This allows the filesystem to "\
@@ -144,6 +153,8 @@ module ApplicationSettingsHelper
       :akismet_api_key,
       :akismet_enabled,
       :auto_devops_enabled,
+      :circuitbreaker_access_retries,
+      :circuitbreaker_backoff_threshold,
       :circuitbreaker_failure_count_threshold,
       :circuitbreaker_failure_reset_time,
       :circuitbreaker_failure_wait_time,

app/helpers/storage_health_helper.rb

@@ -16,17 +16,16 @@ module StorageHealthHelper
   def message_for_circuit_breaker(circuit_breaker)
     maximum_failures = circuit_breaker.failure_count_threshold
     current_failures = circuit_breaker.failure_count
-    permanently_broken = circuit_breaker.circuit_broken? && current_failures >= maximum_failures
 
     translation_params = { number_of_failures: current_failures,
                            maximum_failures: maximum_failures,
                            number_of_seconds: circuit_breaker.failure_wait_time }
 
-    if permanently_broken
+    if circuit_breaker.circuit_broken?
       s_("%{number_of_failures} of %{maximum_failures} failures. GitLab will not "\
          "retry automatically. Reset storage information when the problem is "\
          "resolved.") % translation_params
-    elsif circuit_breaker.circuit_broken?
+    elsif circuit_breaker.backing_off?
       _("%{number_of_failures} of %{maximum_failures} failures. GitLab will "\
         "block access for %{number_of_seconds} seconds.") % translation_params
     else

app/models/application_setting.rb

@@ -153,13 +153,25 @@ class ApplicationSetting < ActiveRecord::Base
             presence: true,
             numericality: { greater_than_or_equal_to: 0 }
 
-  validates :circuitbreaker_failure_count_threshold,
+  validates :circuitbreaker_backoff_threshold,
+            :circuitbreaker_failure_count_threshold,
             :circuitbreaker_failure_wait_time,
             :circuitbreaker_failure_reset_time,
             :circuitbreaker_storage_timeout,
             presence: true,
             numericality: { only_integer: true, greater_than_or_equal_to: 0 }
 
+  validates :circuitbreaker_access_retries,
+            presence: true,
+            numericality: { only_integer: true, greater_than_or_equal_to: 1 }
+
+  validates_each :circuitbreaker_backoff_threshold do |record, attr, value|
+    if value.to_i >= record.circuitbreaker_failure_count_threshold
+      record.errors.add(attr, _("The circuitbreaker backoff threshold should be "\
+                                "lower than the failure count threshold"))
+    end
+  end
+
   SUPPORTED_KEY_TYPES.each do |type|
     validates :"#{type}_key_restriction", presence: true, key_restriction: { type: type }
   end

app/views/admin/application_settings/_form.html.haml

@@ -533,11 +533,23 @@
   %fieldset
     %legend Git Storage Circuitbreaker settings
     .form-group
-      = f.label :circuitbreaker_failure_count_threshold, _('Maximum git storage failures'), class: 'control-label col-sm-2'
+      = f.label :circuitbreaker_access_retries, _('Number of access attempts'), class: 'control-label col-sm-2'
       .col-sm-10
-        = f.number_field :circuitbreaker_failure_count_threshold, class: 'form-control'
+        = f.number_field :circuitbreaker_access_retries, class: 'form-control'
         .help-block
-          = circuitbreaker_failure_count_help_text
+          = circuitbreaker_access_retries_help_text
+    .form-group
+      = f.label :circuitbreaker_storage_timeout, _('Seconds to wait for a storage access attempt'), class: 'control-label col-sm-2'
+      .col-sm-10
+        = f.number_field :circuitbreaker_storage_timeout, class: 'form-control'
+        .help-block
+          = circuitbreaker_storage_timeout_help_text
+    .form-group
+      = f.label :circuitbreaker_backoff_threshold, _('Number of failures before backing off'), class: 'control-label col-sm-2'
+      .col-sm-10
+        = f.number_field :circuitbreaker_backoff_threshold, class: 'form-control'
+        .help-block
+          = circuitbreaker_backoff_threshold_help_text
     .form-group
       = f.label :circuitbreaker_failure_wait_time, _('Seconds to wait after a storage failure'), class: 'control-label col-sm-2'
       .col-sm-10
@@ -545,17 +557,17 @@
         .help-block
           = circuitbreaker_failure_wait_time_help_text
     .form-group
-      = f.label :circuitbreaker_failure_reset_time, _('Seconds before reseting failure information'), class: 'control-label col-sm-2'
+      = f.label :circuitbreaker_failure_count_threshold, _('Maximum git storage failures'), class: 'control-label col-sm-2'
       .col-sm-10
-        = f.number_field :circuitbreaker_failure_reset_time, class: 'form-control'
+        = f.number_field :circuitbreaker_failure_count_threshold, class: 'form-control'
         .help-block
-          = circuitbreaker_failure_reset_time_help_text
+          = circuitbreaker_failure_count_help_text
     .form-group
-      = f.label :circuitbreaker_storage_timeout, _('Seconds to wait for a storage access attempt'), class: 'control-label col-sm-2'
+      = f.label :circuitbreaker_failure_reset_time, _('Seconds before reseting failure information'), class: 'control-label col-sm-2'
       .col-sm-10
-        = f.number_field :circuitbreaker_storage_timeout, class: 'form-control'
+        = f.number_field :circuitbreaker_failure_reset_time, class: 'form-control'
         .help-block
-          = circuitbreaker_storage_timeout_help_text
+          = circuitbreaker_failure_reset_time_help_text
 
   %fieldset
     %legend Repository Checks

changelogs/unreleased/bvl-circuitbreaker-backoff.yml

+---
+title: Make the circuitbreaker more robust by adding higher thresholds, and multiple
+  access attempts.
+merge_request: 14933
+author:
+type: fixed

db/migrate/20171017145932_add_new_circuitbreaker_settings_to_application_settings.rb

+class AddNewCircuitbreakerSettingsToApplicationSettings < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def change
+    add_column :application_settings,
+               :circuitbreaker_access_retries,
+               :integer,
+               default: 3
+    add_column :application_settings,
+               :circuitbreaker_backoff_threshold,
+               :integer,
+               default: 80
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20171012101043) do
+ActiveRecord::Schema.define(version: 20171017145932) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -138,6 +138,8 @@ ActiveRecord::Schema.define(version: 20171012101043) do
     t.integer "circuitbreaker_failure_wait_time", default: 30
     t.integer "circuitbreaker_failure_reset_time", default: 1800
     t.integer "circuitbreaker_storage_timeout", default: 30
+    t.integer "circuitbreaker_access_retries", default: 3
+    t.integer "circuitbreaker_backoff_threshold", default: 80
   end
 
   create_table "audit_events", force: :cascade do |t|

doc/administration/repository_storage_paths.md

@@ -109,6 +109,11 @@ This can be configured from the admin interface:
 
 ![circuitbreaker configuration](img/circuitbreaker_config.png)
 
+**Number of access attempts**: The number of attempts GitLab will make to access a
+storage when probing a shard.
+
+**Number of failures before backing off**: The number of failures after which
+GitLab will start temporarily disabling access to a storage shard on a host.
 
 **Maximum git storage failures:** The number of failures of after which GitLab will
 completely prevent access to the storage. The number of failures can be reset in
@@ -126,6 +131,15 @@ mount is reset.
 **Seconds to wait for a storage access attempt:** The time in seconds GitLab will
 try to access storage. After this time a timeout error will be raised.
 
+To enable the circuitbreaker for repository storage you can flip the feature flag from a rails console:
+
+```
+Feature.enable('git_storage_circuit_breaker')
+```
+
+Alternatively it can be enabled by setting `true` in the `GIT_STORAGE_CIRCUIT_BREAKER` environment variable.
+This approach would be used when enabling the circuit breaker on a single host.
+
 When storage failures occur, this will be visible in the admin interface like this:
 
 ![failing storage](img/failing_storage.png)

doc/api/settings.md

@@ -69,6 +69,8 @@ PUT /application/settings
 | `after_sign_up_text`                     | string           | no                                            | Text shown to the user after signing up                                                                                                                                                                                                                                                                                                                                                                                                                   |
 | `akismet_api_key`                        | string           | no                                            | API key for akismet spam protection                                                                                                                                                                                                                                                                                                                                                                                                                       |
 | `akismet_enabled`                        | boolean          | no                                            | Enable or disable akismet spam protection                                                                                                                                                                                                                                                                                                                                                                                                                 |
+| `circuitbreaker_access_retries           | integer          | no                                            | The number of attempts GitLab will make to access a storage.                                                                                                                                                                                                                                                                                                                                                                                              |
+| `circuitbreaker_backoff_threshold        | integer          | no                                            | The number of failures after which GitLab will start temporarily disabling access to a storage shard on a host.                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
 | `circuitbreaker_failure_count_threshold` | integer          | no                                            | The number of failures of after which GitLab will completely prevent access to the storage.                                                                                                                                                                                                                                                                                                                                                               |
 | `circuitbreaker_failure_reset_time`      | integer          | no                                            | Time in seconds GitLab will keep storage failure information. When no failures occur during this time, the failure information is reset.                                                                                                                                                                                                                                                                                                                  |
 | `circuitbreaker_failure_wait_time`       | integer          | no                                            | Time in seconds GitLab will block access to a failing storage to allow it to recover.                                                                                                                                                                                                                                                                                                                                                                     |

lib/gitlab/git/storage.rb

@@ -12,6 +12,7 @@ module Gitlab
 
       CircuitOpen = Class.new(Inaccessible)
       Misconfiguration = Class.new(Inaccessible)
+      Failing = Class.new(Inaccessible)
 
       REDIS_KEY_PREFIX = 'storage_accessible:'.freeze
 

lib/gitlab/git/storage/circuit_breaker.rb

@@ -54,7 +54,7 @@ module Gitlab
         end
 
         def perform
-          return yield unless Feature.enabled?('git_storage_circuit_breaker')
+          return yield unless enabled?
 
           check_storage_accessible!
 
@@ -64,10 +64,27 @@ module Gitlab
         def circuit_broken?
           return false if no_failures?
 
+          failure_count > failure_count_threshold
+        end
+
+        def backing_off?
+          return false if no_failures?
+
           recent_failure = last_failure > failure_wait_time.seconds.ago
-          too_many_failures = failure_count > failure_count_threshold
+          too_many_failures = failure_count > backoff_threshold
 
-          recent_failure || too_many_failures
+          recent_failure && too_many_failures
+        end
+
+        private
+
+        # The circuitbreaker can be enabled for the entire fleet using a Feature
+        # flag.
+        #
+        # Enabling it for a single host can be done setting the
+        # `GIT_STORAGE_CIRCUIT_BREAKER` environment variable.
+        def enabled?
+          ENV['GIT_STORAGE_CIRCUIT_BREAKER'].present? || Feature.enabled?('git_storage_circuit_breaker')
         end
 
         def failure_info
@@ -83,7 +100,7 @@ module Gitlab
           return @storage_available if @storage_available
 
           if @storage_available = Gitlab::Git::Storage::ForkedStorageCheck
-                                    .storage_available?(storage_path, storage_timeout)
+                                    .storage_available?(storage_path, storage_timeout, access_retries)
             track_storage_accessible
           else
             track_storage_inaccessible
@@ -94,7 +111,11 @@ module Gitlab
 
         def check_storage_accessible!
           if circuit_broken?
-            raise Gitlab::Git::Storage::CircuitOpen.new("Circuit for #{storage} is broken", failure_wait_time)
+            raise Gitlab::Git::Storage::CircuitOpen.new("Circuit for #{storage} is broken", failure_reset_time)
+          end
+
+          if backing_off?
+            raise Gitlab::Git::Storage::Failing.new("Backing off access to #{storage}", failure_wait_time)
           end
 
           unless storage_available?
@@ -131,12 +152,6 @@ module Gitlab
           end
         end
 
-        def cache_key
-          @cache_key ||= "#{Gitlab::Git::Storage::REDIS_KEY_PREFIX}#{storage}:#{hostname}"
-        end
-
-        private
-
         def get_failure_info
           last_failure, failure_count = Gitlab::Git::Storage.redis.with do |redis|
             redis.hmget(cache_key, :last_failure, :failure_count)
@@ -146,6 +161,10 @@ module Gitlab
 
           FailureInfo.new(last_failure, failure_count.to_i)
         end
+
+        def cache_key
+          @cache_key ||= "#{Gitlab::Git::Storage::REDIS_KEY_PREFIX}#{storage}:#{hostname}"
+        end
       end
     end
   end

lib/gitlab/git/storage/circuit_breaker_settings.rb

@@ -18,6 +18,14 @@ module Gitlab
           application_settings.circuitbreaker_storage_timeout
         end
 
+        def access_retries
+          application_settings.circuitbreaker_access_retries
+        end
+
+        def backoff_threshold
+          application_settings.circuitbreaker_backoff_threshold
+        end
+
         private
 
         def application_settings

lib/gitlab/git/storage/forked_storage_check.rb

@@ -4,8 +4,17 @@ module Gitlab
       module ForkedStorageCheck
         extend self
 
-        def storage_available?(path, timeout_seconds = 5)
-          status = timeout_check(path, timeout_seconds)
+        def storage_available?(path, timeout_seconds = 5, retries = 1)
+          partial_timeout = timeout_seconds / retries
+          status = timeout_check(path, partial_timeout)
+
+          # If the status check did not succeed the first time, we retry a few
+          # more times to avoid one-off failures
+          current_attempts = 1
+          while current_attempts < retries && !status.success?
+            status = timeout_check(path, partial_timeout)
+            current_attempts += 1
+          end
 
           status.success?
         end

lib/gitlab/git/storage/null_circuit_breaker.rb

@@ -25,6 +25,10 @@ module Gitlab
           !!@error
         end
 
+        def backing_off?
+          false
+        end
+
         def last_failure
           circuit_broken? ? Time.now : nil
         end

spec/lib/gitlab/git/storage/forked_storage_check_spec.rb

@@ -33,6 +33,21 @@ describe Gitlab::Git::Storage::ForkedStorageCheck, broken_storage: true, skip_da
       expect(runtime).to be < 1.0
     end
 
+    it 'will try the specified amount of times before failing'  do
+      allow(described_class).to receive(:check_filesystem_in_process) do
+        Process.spawn("sleep 10")
+      end
+
+      expect(Process).to receive(:spawn).with('sleep 10').twice
+                           .and_call_original
+
+      runtime = Benchmark.realtime do
+        described_class.storage_available?(existing_path, 0.5, 2)
+      end
+
+      expect(runtime).to be < 1.0
+    end
+
     describe 'when using paths with spaces' do
       let(:test_dir) { Rails.root.join('tmp', 'tests', 'storage_check') }
       let(:path_with_spaces) { File.join(test_dir, 'path with spaces') }

spec/lib/gitlab/git/storage/null_circuit_breaker_spec.rb

@@ -65,17 +65,6 @@ describe Gitlab::Git::Storage::NullCircuitBreaker do
     ours = described_class.public_instance_methods
     theirs = Gitlab::Git::Storage::CircuitBreaker.public_instance_methods
 
-    # These methods are not part of the public API, but are public to allow the
-    # CircuitBreaker specs to operate. They should be made private over time.
-    exceptions = %i[
-      cache_key
-      check_storage_accessible!
-      no_failures?
-      storage_available?
-      track_storage_accessible
-      track_storage_inaccessible
-    ]
-
-    expect(theirs - ours).to contain_exactly(*exceptions)
+    expect(theirs - ours).to be_empty
   end
 end

spec/models/application_setting_spec.rb

@@ -115,7 +115,8 @@ describe ApplicationSetting do
     end
 
     context 'circuitbreaker settings' do
-      [:circuitbreaker_failure_count_threshold,
+      [:circuitbreaker_backoff_threshold,
+       :circuitbreaker_failure_count_threshold,
        :circuitbreaker_failure_wait_time,
        :circuitbreaker_failure_reset_time,
        :circuitbreaker_storage_timeout].each do |field|
@@ -125,6 +126,16 @@ describe ApplicationSetting do
                            .is_greater_than_or_equal_to(0)
         end
       end
+
+      it 'requires the `backoff_threshold` to be lower than the `failure_count_threshold`' do
+        setting.circuitbreaker_failure_count_threshold = 10
+        setting.circuitbreaker_backoff_threshold = 15
+        failure_message = "The circuitbreaker backoff threshold should be lower "\
+                          "than the failure count threshold"
+
+        expect(setting).not_to be_valid
+        expect(setting.errors[:circuitbreaker_backoff_threshold]).to include(failure_message)
+      end
     end
 
     context 'repository storages' do