Merge branch 'build-chunks-on-object-storage' into 'master'

Allow to store BuildTraceChunks on Object Storage

Closes #45712

See merge request gitlab-org/gitlab-ce!19515

app/models/ci/build_trace_chunk.rb

 module Ci
   class BuildTraceChunk < ActiveRecord::Base
     include FastDestroyAll
+    include ::Gitlab::ExclusiveLeaseHelpers
     extend Gitlab::Ci::Model
     belongs_to :build, class_name: "Ci::Build", foreign_key: :build_id
     default_value_for :data_store, :redis
-    WriteError = Class.new(StandardError)
-
     CHUNK_SIZE = 128.kilobytes
-    CHUNK_REDIS_TTL = 1.week
     WRITE_LOCK_RETRY = 10
     WRITE_LOCK_SLEEP = 0.01.seconds
     WRITE_LOCK_TTL = 1.minute
+    # Note: The ordering of this enum is related to the precedence of persist store.
+    # The bottom item takes the higest precedence, and the top item takes the lowest precedence.
     enum data_store: {
       redis: 1,
-      db: 2
+      database: 2,
+      fog: 3
     }
     class << self
-      def redis_data_key(build_id, chunk_index)
-        "gitlab:ci:trace:#{build_id}:chunks:#{chunk_index}"
+      def all_stores
+        @all_stores ||= self.data_stores.keys
       end
-      def redis_data_keys
-        redis.pluck(:build_id, :chunk_index).map do |data|
-          redis_data_key(data.first, data.second)
-        end
+      def persistable_store
+        # get first available store from the back of the list
+        all_stores.reverse.find { |store| get_store_class(store).available? }
       end
-      def redis_delete_data(keys)
-        return if keys.empty?
-
-        Gitlab::Redis::SharedState.with do |redis|
-          redis.del(keys)
-        end
+      def get_store_class(store)
+        @stores ||= {}
+        @stores[store] ||= "Ci::BuildTraceChunks::#{store.capitalize}".constantize.new
       end
       ##
       # FastDestroyAll concerns
       def begin_fast_destroy
-        redis_data_keys
+        all_stores.each_with_object({}) do |store, result|
+          relation = public_send(store) # rubocop:disable GitlabSecurity/PublicSend
+          keys = get_store_class(store).keys(relation)
+
+          result[store] = keys if keys.present?
+        end
       end
       ##
       # FastDestroyAll concerns
       def finalize_fast_destroy(keys)
-        redis_delete_data(keys)
+        keys.each do |store, value|
+          get_store_class(store).delete_keys(value)
+        end
       end
     end
@@ -66,10 +70,15 @@ module Ci
     end
     def append(new_data, offset)
+      raise ArgumentError, 'New data is missing' unless new_data
       raise ArgumentError, 'Offset is out of range' if offset > size || offset < 0
       raise ArgumentError, 'Chunk size overflow' if CHUNK_SIZE < (offset + new_data.bytesize)
-      set_data(data.byteslice(0, offset) + new_data)
+      in_lock(*lock_params) do # Write opetation is atomic
+        unsafe_set_data!(data.byteslice(0, offset) + new_data)
+      end
+
+      schedule_to_persist if full?
     end
     def size
@@ -88,93 +97,63 @@ module Ci
       (start_offset...end_offset)
     end
-    def use_database!
-      in_lock do
-        break if db?
-        break unless size > 0
-
-        self.update!(raw_data: data, data_store: :db)
-        self.class.redis_delete_data([redis_data_key])
+    def persist_data!
+      in_lock(*lock_params) do # Write opetation is atomic
+        unsafe_persist_to!(self.class.persistable_store)
       end
     end
     private
-    def get_data
-      if redis?
-        redis_data
-      elsif db?
-        raw_data
-      else
-        raise 'Unsupported data store'
-      end&.force_encoding(Encoding::BINARY) # Redis/Database return UTF-8 string as default
-    end
-
-    def set_data(value)
-      raise ArgumentError, 'too much data' if value.bytesize > CHUNK_SIZE
-
-      in_lock do
-        if redis?
-          redis_set_data(value)
-        elsif db?
-          self.raw_data = value
-        else
-          raise 'Unsupported data store'
-        end
-        @data = value
-        save! if changed?
+    def unsafe_persist_to!(new_store)
+      return if data_store == new_store.to_s
+      raise ArgumentError, 'Can not persist empty data' unless size > 0
+      old_store_class = self.class.get_store_class(data_store)
+      get_data.tap do |the_data|
+        self.raw_data = nil
+        self.data_store = new_store
+        unsafe_set_data!(the_data)
       end
-      schedule_to_db if full?
-    end
-
-    def schedule_to_db
-      return if db?
-
-      Ci::BuildTraceChunkFlushWorker.perform_async(id)
+      old_store_class.delete_data(self)
     end
-    def full?
-      size == CHUNK_SIZE
+    def get_data
+      self.class.get_store_class(data_store).data(self)&.force_encoding(Encoding::BINARY) # Redis/Database return UTF-8 string as default
+    rescue Excon::Error::NotFound
+      # If the data store is :fog and the file does not exist in the object storage, this method returns nil.
     end
-    def redis_data
-      Gitlab::Redis::SharedState.with do |redis|
-        redis.get(redis_data_key)
-      end
-    end
-    def redis_set_data(data)
-      Gitlab::Redis::SharedState.with do |redis|
-        redis.set(redis_data_key, data, ex: CHUNK_REDIS_TTL)
-      end
-    end
-    def redis_data_key
-      self.class.redis_data_key(build_id, chunk_index)
+    def unsafe_set_data!(value)
+      raise ArgumentError, 'New data size exceeds chunk size' if value.bytesize > CHUNK_SIZE
+      self.class.get_store_class(data_store).set_data(self, value)
+      @data = value
+      save! if changed?
     end
-    def in_lock
-      write_lock_key = "trace_write:#{build_id}:chunks:#{chunk_index}"
-      lease = Gitlab::ExclusiveLease.new(write_lock_key, timeout: WRITE_LOCK_TTL)
-      retry_count = 0
-      until uuid = lease.try_obtain
-        # Keep trying until we obtain the lease. To prevent hammering Redis too
-        # much we'll wait for a bit between retries.
-        sleep(WRITE_LOCK_SLEEP)
-        break if WRITE_LOCK_RETRY < (retry_count += 1)
-      end
-      raise WriteError, 'Failed to obtain write lock' unless uuid
-      self.reload if self.persisted?
-      return yield
-    ensure
-      Gitlab::ExclusiveLease.cancel(write_lock_key, uuid)
+    def schedule_to_persist
+      return if data_persisted?
+      Ci::BuildTraceChunkFlushWorker.perform_async(id)
+    end
+    def data_persisted?
+      !redis?
+    end
+    def full?
+      size == CHUNK_SIZE
+    end
+    def lock_params
+      ["trace_write:#{build_id}:chunks:#{chunk_index}",
+       { ttl: WRITE_LOCK_TTL,
+         retries: WRITE_LOCK_RETRY,
+         sleep_sec: WRITE_LOCK_SLEEP }]
     end
   end
 end

app/models/ci/build_trace_chunks/database.rb

+module Ci
+  module BuildTraceChunks
+    class Database
+      def available?
+        true
+      end
+
+      def keys(relation)
+        []
+      end
+
+      def delete_keys(keys)
+        # no-op
+      end
+
+      def data(model)
+        model.raw_data
+      end
+
+      def set_data(model, data)
+        model.raw_data = data
+      end
+
+      def delete_data(model)
+        model.update_columns(raw_data: nil) unless model.raw_data.nil?
+      end
+    end
+  end
+end

app/models/ci/build_trace_chunks/fog.rb

+module Ci
+  module BuildTraceChunks
+    class Fog
+      def available?
+        object_store.enabled
+      end
+
+      def data(model)
+        connection.get_object(bucket_name, key(model))[:body]
+      end
+
+      def set_data(model, data)
+        connection.put_object(bucket_name, key(model), data)
+      end
+
+      def delete_data(model)
+        delete_keys([[model.build_id, model.chunk_index]])
+      end
+
+      def keys(relation)
+        return [] unless available?
+
+        relation.pluck(:build_id, :chunk_index)
+      end
+
+      def delete_keys(keys)
+        keys.each do |key|
+          connection.delete_object(bucket_name, key_raw(*key))
+        end
+      end
+
+      private
+
+      def key(model)
+        key_raw(model.build_id, model.chunk_index)
+      end
+
+      def key_raw(build_id, chunk_index)
+        "tmp/builds/#{build_id.to_i}/chunks/#{chunk_index.to_i}.log"
+      end
+
+      def bucket_name
+        return unless available?
+
+        object_store.remote_directory
+      end
+
+      def connection
+        return unless available?
+
+        @connection ||= ::Fog::Storage.new(object_store.connection.to_hash.deep_symbolize_keys)
+      end
+
+      def object_store
+        Gitlab.config.artifacts.object_store
+      end
+    end
+  end
+end

app/models/ci/build_trace_chunks/redis.rb

+module Ci
+  module BuildTraceChunks
+    class Redis
+      CHUNK_REDIS_TTL = 1.week
+
+      def available?
+        true
+      end
+
+      def data(model)
+        Gitlab::Redis::SharedState.with do |redis|
+          redis.get(key(model))
+        end
+      end
+
+      def set_data(model, data)
+        Gitlab::Redis::SharedState.with do |redis|
+          redis.set(key(model), data, ex: CHUNK_REDIS_TTL)
+        end
+      end
+
+      def delete_data(model)
+        delete_keys([[model.build_id, model.chunk_index]])
+      end
+
+      def keys(relation)
+        relation.pluck(:build_id, :chunk_index)
+      end
+
+      def delete_keys(keys)
+        return if keys.empty?
+
+        keys = keys.map { |key| key_raw(*key) }
+
+        Gitlab::Redis::SharedState.with do |redis|
+          redis.del(keys)
+        end
+      end
+
+      private
+
+      def key(model)
+        key_raw(model.build_id, model.chunk_index)
+      end
+
+      def key_raw(build_id, chunk_index)
+        "gitlab:ci:trace:#{build_id.to_i}:chunks:#{chunk_index.to_i}"
+      end
+    end
+  end
+end

app/workers/ci/build_trace_chunk_flush_worker.rb

@@ -7,7 +7,7 @@ module Ci
     def perform(build_trace_chunk_id)
       ::Ci::BuildTraceChunk.find_by(id: build_trace_chunk_id).try do |build_trace_chunk|
-        build_trace_chunk.use_database!
+        build_trace_chunk.persist_data!
       end
     end
   end

changelogs/unreleased/build-chunks-on-object-storage.yml

+---
+title: Use object storage as the first class persistable store for new live trace
+  architecture
+merge_request: 19515
+author:
+type: changed

doc/administration/job_traces.md

@@ -77,10 +77,10 @@ cloud-native, for example on Kubernetes.
 The data flow is the same as described in the [data flow section](#data-flow)
 with one change: _the stored path of the first two phases is different_. This new live
-trace architecture stores chunks of traces in Redis and the database instead of
+trace architecture stores chunks of traces in Redis and a persistent store (object storage or database) instead of
 file storage. Redis is used as first-class storage, and it stores up-to 128KB
-of data. Once the full chunk is sent, it is flushed to database. After a while,
-the data in Redis and database will be archived to [object storage](#uploading-traces-to-object-storage).
+of data. Once the full chunk is sent, it is flushed a persistent store, either object storage(temporary directory) or database.
+After a while, the data in Redis and a persitent store will be archived to [object storage](#uploading-traces-to-object-storage).
 The data are stored in the following Redis namespace: `Gitlab::Redis::SharedState`.
@@ -89,11 +89,11 @@ Here is the detailed data flow:
 1. GitLab Runner picks a job from GitLab
 1. GitLab Runner sends a piece of trace to GitLab
 1. GitLab appends the data to Redis
-1. Once the data in Redis reach 128KB, the data is flushed to the database.
+1. Once the data in Redis reach 128KB, the data is flushed to a persistent store (object storage or the database).
 1. The above steps are repeated until the job is finished.
 1. Once the job is finished, GitLab schedules a Sidekiq worker to archive the trace.
 1. The Sidekiq worker archives the trace to object storage and cleans up the trace
-   in Redis and the database.
+   in Redis and a persistent store (object storage or the database).
 ### Enabling live trace

lib/gitlab/exclusive_lease_helpers.rb

+module Gitlab
+  # This module provides helper methods which are intregrated with GitLab::ExclusiveLease
+  module ExclusiveLeaseHelpers
+    FailedToObtainLockError = Class.new(StandardError)
+
+    ##
+    # This helper method blocks a process/thread until the other process cancel the obrainted lease key.
+    #
+    # Note: It's basically discouraged to use this method in the unicorn's thread,
+    #       because it holds the connection until all `retries` is consumed.
+    #       This could potentially eat up all connection pools.
+    def in_lock(key, ttl: 1.minute, retries: 10, sleep_sec: 0.01.seconds)
+      lease = Gitlab::ExclusiveLease.new(key, timeout: ttl)
+
+      until uuid = lease.try_obtain
+        # Keep trying until we obtain the lease. To prevent hammering Redis too
+        # much we'll wait for a bit.
+        sleep(sleep_sec)
+        break if (retries -= 1) < 0
+      end
+
+      raise FailedToObtainLockError, 'Failed to obtain a lock' unless uuid
+
+      return yield
+    ensure
+      Gitlab::ExclusiveLease.cancel(key, uuid)
+    end
+  end
+end

spec/factories/ci/build_trace_chunks.rb

@@ -3,5 +3,53 @@ FactoryBot.define do
     build factory: :ci_build
     chunk_index 0
     data_store :redis
+
+    trait :redis_with_data do
+      data_store :redis
+
+      transient do
+        initial_data 'test data'
+      end
+
+      after(:create) do |build_trace_chunk, evaluator|
+        Ci::BuildTraceChunks::Redis.new.set_data(build_trace_chunk, evaluator.initial_data)
+      end
+    end
+
+    trait :redis_without_data do
+      data_store :redis
+    end
+
+    trait :database_with_data do
+      data_store :database
+
+      transient do
+        initial_data 'test data'
+      end
+
+      after(:build) do |build_trace_chunk, evaluator|
+        Ci::BuildTraceChunks::Database.new.set_data(build_trace_chunk, evaluator.initial_data)
+      end
+    end
+
+    trait :database_without_data do
+      data_store :database
+    end
+
+    trait :fog_with_data do
+      data_store :fog
+
+      transient do
+        initial_data 'test data'
+      end
+
+      after(:create) do |build_trace_chunk, evaluator|
+        Ci::BuildTraceChunks::Fog.new.set_data(build_trace_chunk, evaluator.initial_data)
+      end
+    end
+
+    trait :fog_without_data do
+      data_store :fog
+    end
   end
 end

spec/lib/gitlab/exclusive_lease_helpers_spec.rb

+require 'spec_helper'
+
+describe Gitlab::ExclusiveLeaseHelpers, :clean_gitlab_redis_shared_state do
+  include ::ExclusiveLeaseHelpers
+
+  let(:class_instance) { (Class.new { include ::Gitlab::ExclusiveLeaseHelpers }).new }
+  let(:unique_key) { SecureRandom.hex(10) }
+
+  describe '#in_lock' do
+    subject { class_instance.in_lock(unique_key, **options) { } }
+
+    let(:options) { {} }
+
+    context 'when the lease is not obtained yet' do
+      before do
+        stub_exclusive_lease(unique_key, 'uuid')
+      end
+
+      it 'calls the given block' do
+        expect { |b| class_instance.in_lock(unique_key, &b) }.to yield_control.once
+      end
+
+      it 'calls the given block continuously' do
+        expect { |b| class_instance.in_lock(unique_key, &b) }.to yield_control.once
+        expect { |b| class_instance.in_lock(unique_key, &b) }.to yield_control.once
+        expect { |b| class_instance.in_lock(unique_key, &b) }.to yield_control.once
+      end
+
+      it 'cancels the exclusive lease after the block' do
+        expect_to_cancel_exclusive_lease(unique_key, 'uuid')
+
+        subject
+      end
+    end
+
+    context 'when the lease is obtained already' do
+      let!(:lease) { stub_exclusive_lease_taken(unique_key) }
+
+      it 'retries to obtain a lease and raises an error' do
+        expect(lease).to receive(:try_obtain).exactly(11).times
+
+        expect { subject }.to raise_error('Failed to obtain a lock')
+      end
+
+      context 'when ttl is specified' do
+        let(:options) { { ttl: 10.minutes } }
+
+        it 'receives the specified argument' do
+          expect(Gitlab::ExclusiveLease).to receive(:new).with(unique_key, { timeout: 10.minutes } )
+
+          expect { subject }.to raise_error('Failed to obtain a lock')
+        end
+      end
+
+      context 'when retry count is specified' do
+        let(:options) { { retries: 3 } }
+
+        it 'retries for the specified times' do
+          expect(lease).to receive(:try_obtain).exactly(4).times
+
+          expect { subject }.to raise_error('Failed to obtain a lock')
+        end
+      end
+
+      context 'when sleep second is specified' do
+        let(:options) { { retries: 0, sleep_sec: 0.05.seconds } }
+
+        it 'receives the specified argument' do
+          expect(class_instance).to receive(:sleep).with(0.05.seconds).once
+
+          expect { subject }.to raise_error('Failed to obtain a lock')
+        end
+      end
+    end
+  end
+end

spec/models/ci/build_trace_chunk_spec.rb

@@ -14,6 +14,7 @@ describe Ci::BuildTraceChunk, :clean_gitlab_redis_shared_state do
   before do
     stub_feature_flags(ci_enable_live_trace: true)
+    stub_artifacts_object_storage
   end
   context 'FastDestroyAll' do
@@ -37,6 +38,22 @@ describe Ci::BuildTraceChunk, :clean_gitlab_redis_shared_state do
     end
   end
+  describe '.all_stores' do
+    subject { described_class.all_stores }
+
+    it 'returns a correctly ordered array' do
+      is_expected.to eq(%w[redis database fog])
+    end
+
+    it 'returns redis store as the the lowest precedence' do
+      expect(subject.first).to eq('redis')
+    end
+
+    it 'returns fog store as the the highest precedence' do
+      expect(subject.last).to eq('fog')
+    end
+  end
+
   describe '#data' do
     subject { build_trace_chunk.data }
@@ -44,181 +61,269 @@ describe Ci::BuildTraceChunk, :clean_gitlab_redis_shared_state do
       let(:data_store) { :redis }
       before do
-        build_trace_chunk.send(:redis_set_data, 'Sample data in redis')
+        build_trace_chunk.send(:unsafe_set_data!, 'Sample data in redis')
       end
       it { is_expected.to eq('Sample data in redis') }
     end
     context 'when data_store is database' do
-      let(:data_store) { :db }
-      let(:raw_data) { 'Sample data in db' }
-      it { is_expected.to eq('Sample data in db') }
+      let(:data_store) { :database }
+      let(:raw_data) { 'Sample data in database' }
+      it { is_expected.to eq('Sample data in database') }
     end
-  end
-
-  describe '#set_data' do
-    subject { build_trace_chunk.send(:set_data, value) }
-    let(:value) { 'Sample data' }
-    context 'when value bytesize is bigger than CHUNK_SIZE' do
-      let(:value) { 'a' * (described_class::CHUNK_SIZE + 1) }
-      it { expect { subject }.to raise_error('too much data') }
+    context 'when data_store is fog' do
+      let(:data_store) { :fog }
+      before do
+        build_trace_chunk.send(:unsafe_set_data!, 'Sample data in fog')
+      end
+      it { is_expected.to eq('Sample data in fog') }
     end
-    context 'when data_store is redis' do
-      let(:data_store) { :redis }
-      it do
-        expect(build_trace_chunk.send(:redis_data)).to be_nil
-        subject
-        expect(build_trace_chunk.send(:redis_data)).to eq(value)
+  end
+  describe '#append' do
+    subject { build_trace_chunk.append(new_data, offset) }
+    let(:new_data) { 'Sample new data' }
+    let(:offset) { 0 }
+    let(:merged_data) { data + new_data.to_s }
+    shared_examples_for 'Appending correctly' do
+      context 'when offset is negative' do
+        let(:offset) { -1 }
+
+        it { expect { subject }.to raise_error('Offset is out of range') }
+      end
+      context 'when offset is bigger than data size' do
+        let(:offset) { data.bytesize + 1 }
+
+        it { expect { subject }.to raise_error('Offset is out of range') }
       end
-      context 'when fullfilled chunk size' do
-        let(:value) { 'a' * described_class::CHUNK_SIZE }
-        it 'schedules stashing data' do
-          expect(Ci::BuildTraceChunkFlushWorker).to receive(:perform_async).once
+      context 'when new data overflows chunk size' do
+        let(:new_data) { 'a' * (described_class::CHUNK_SIZE + 1) }
+        it { expect { subject }.to raise_error('Chunk size overflow') }
+      end
+
+      context 'when offset is EOF' do
+        let(:offset) { data.bytesize }
+        it 'appends' do
           subject
+
+          expect(build_trace_chunk.data).to eq(merged_data)
         end
-      end
-    end
-    context 'when data_store is database' do
-      let(:data_store) { :db }
-      it 'sets data' do
-        expect(build_trace_chunk.raw_data).to be_nil
-        subject
-        expect(build_trace_chunk.raw_data).to eq(value)
-        expect(build_trace_chunk.persisted?).to be_truthy
-      end
-      context 'when raw_data is not changed' do
-        it 'does not execute UPDATE' do
-          expect(build_trace_chunk.raw_data).to be_nil
-          build_trace_chunk.save!
-          # First set
-          expect(ActiveRecord::QueryRecorder.new { subject }.count).to be > 0
-          expect(build_trace_chunk.raw_data).to eq(value)
-          expect(build_trace_chunk.persisted?).to be_truthy
-          # Second set
-          build_trace_chunk.reload
-          expect(ActiveRecord::QueryRecorder.new { subject }.count).to be(0)
+        context 'when the other process is appending' do
+          let(:lease_key) { "trace_write:#{build_trace_chunk.build.id}:chunks:#{build_trace_chunk.chunk_index}" }
+          before do
+            stub_exclusive_lease_taken(lease_key)
+          end
+          it 'raise an error' do
+            expect { subject }.to raise_error('Failed to obtain a lock')
+          end
+        end
+        context 'when new_data is nil' do
+          let(:new_data) { nil }
+          it 'raises an error' do
+            expect { subject }.to raise_error('New data is missing')
+          end
+        end
+        context 'when new_data is empty' do
+          let(:new_data) { '' }
+          it 'does not append' do
+            subject
+
+            expect(build_trace_chunk.data).to eq(data)
+          end
+
+          it 'does not execute UPDATE' do
+            ActiveRecord::QueryRecorder.new { subject }.log.map do |query|
+              expect(query).not_to include('UPDATE')
+            end
+          end
         end
       end
-      context 'when fullfilled chunk size' do
-        it 'does not schedule stashing data' do
-          expect(Ci::BuildTraceChunkFlushWorker).not_to receive(:perform_async)
+      context 'when offset is middle of datasize' do
+        let(:offset) { data.bytesize / 2 }
+        it 'appends' do
           subject
+
+          expect(build_trace_chunk.data).to eq(data.byteslice(0, offset) + new_data)
         end
       end
     end
-  end
-  describe '#truncate' do
-    subject { build_trace_chunk.truncate(offset) }
-    shared_examples_for 'truncates' do
-      context 'when offset is negative' do
-        let(:offset) { -1 }
-        it { expect { subject }.to raise_error('Offset is out of range') }
-      end
-      context 'when offset is bigger than data size' do
-        let(:offset) { data.bytesize + 1 }
-        it { expect { subject }.to raise_error('Offset is out of range') }
+    shared_examples_for 'Scheduling sidekiq worker to flush data to persist store' do
+      context 'when new data fullfilled chunk size' do
+        let(:new_data) { 'a' * described_class::CHUNK_SIZE }
+        it 'schedules trace chunk flush worker' do
+          expect(Ci::BuildTraceChunkFlushWorker).to receive(:perform_async).once
+          subject
+        end
+        it 'migrates data to object storage' do
+          Sidekiq::Testing.inline! do
+            subject
+            build_trace_chunk.reload
+            expect(build_trace_chunk.fog?).to be_truthy
+            expect(build_trace_chunk.data).to eq(new_data)
+          end
+        end
       end
-      context 'when offset is 10' do
-        let(:offset) { 10 }
-        it 'truncates' do
+    end
+    shared_examples_for 'Scheduling no sidekiq worker' do
+      context 'when new data fullfilled chunk size' do
+        let(:new_data) { 'a' * described_class::CHUNK_SIZE }
+
+        it 'does not schedule trace chunk flush worker' do
+          expect(Ci::BuildTraceChunkFlushWorker).not_to receive(:perform_async)
           subject
-          expect(build_trace_chunk.data).to eq(data.byteslice(0, offset))
+        end
+        it 'does not migrate data to object storage' do
+          Sidekiq::Testing.inline! do
+            data_store = build_trace_chunk.data_store
+
+            subject
+
+            build_trace_chunk.reload
+            expect(build_trace_chunk.data_store).to eq(data_store)
+          end
         end
       end
     end
     context 'when data_store is redis' do
       let(:data_store) { :redis }
-      let(:data) { 'Sample data in redis' }
-      before do
-        build_trace_chunk.send(:redis_set_data, data)
+      context 'when there are no data' do
+        let(:data) { '' }
+
+        it 'has no data' do
+          expect(build_trace_chunk.data).to be_empty
+        end
+
+        it_behaves_like 'Appending correctly'
+        it_behaves_like 'Scheduling sidekiq worker to flush data to persist store'
       end
-      it_behaves_like 'truncates'
-    end
-    context 'when data_store is database' do
-      let(:data_store) { :db }
-      let(:raw_data) { 'Sample data in db' }
-      let(:data) { raw_data }
-      it_behaves_like 'truncates'
+      context 'when there are some data' do
+        let(:data) { 'Sample data in redis' }
+        before do
+          build_trace_chunk.send(:unsafe_set_data!, data)
+        end
+        it 'has data' do
+          expect(build_trace_chunk.data).to eq(data)
+        end
+
+        it_behaves_like 'Appending correctly'
+        it_behaves_like 'Scheduling sidekiq worker to flush data to persist store'
+      end
     end
-  end
-  describe '#append' do
-    subject { build_trace_chunk.append(new_data, offset) }
-    let(:new_data) { 'Sample new data' }
-    let(:offset) { 0 }
-    let(:total_data) { data + new_data }
-    shared_examples_for 'appends' do
-      context 'when offset is negative' do
-        let(:offset) { -1 }
-        it { expect { subject }.to raise_error('Offset is out of range') }
+    context 'when data_store is database' do
+      let(:data_store) { :database }
+      context 'when there are no data' do
+        let(:data) { '' }
+        it 'has no data' do
+          expect(build_trace_chunk.data).to be_empty
+        end
+        it_behaves_like 'Appending correctly'
+        it_behaves_like 'Scheduling no sidekiq worker'
       end
-      context 'when offset is bigger than data size' do
-        let(:offset) { data.bytesize + 1 }
-        it { expect { subject }.to raise_error('Offset is out of range') }
+      context 'when there are some data' do
+        let(:raw_data) { 'Sample data in database' }
+        let(:data) { raw_data }
+        it 'has data' do
+          expect(build_trace_chunk.data).to eq(data)
+        end
+
+        it_behaves_like 'Appending correctly'
+        it_behaves_like 'Scheduling no sidekiq worker'
       end
-      context 'when offset is bigger than data size' do
-        let(:new_data) { 'a' * (described_class::CHUNK_SIZE + 1) }
-        it { expect { subject }.to raise_error('Chunk size overflow') }
+    end
+    context 'when data_store is fog' do
+      let(:data_store) { :fog }
+      context 'when there are no data' do
+        let(:data) { '' }
+
+        it 'has no data' do
+          expect(build_trace_chunk.data).to be_empty
+        end
+
+        it_behaves_like 'Appending correctly'
+        it_behaves_like 'Scheduling no sidekiq worker'
       end
-      context 'when offset is EOF' do
-        let(:offset) { data.bytesize }
-        it 'appends' do
-          subject
-          expect(build_trace_chunk.data).to eq(total_data)
+      context 'when there are some data' do
+        let(:data) { 'Sample data in fog' }
+        before do
+          build_trace_chunk.send(:unsafe_set_data!, data)
+        end
+        it 'has data' do
+          expect(build_trace_chunk.data).to eq(data)
         end
+
+        it_behaves_like 'Appending correctly'
+        it_behaves_like 'Scheduling no sidekiq worker'
+      end
+    end
+  end
+
+  describe '#truncate' do
+    subject { build_trace_chunk.truncate(offset) }
+
+    shared_examples_for 'truncates' do
+      context 'when offset is negative' do
+        let(:offset) { -1 }
+
+        it { expect { subject }.to raise_error('Offset is out of range') }
+      end
+
+      context 'when offset is bigger than data size' do
+        let(:offset) { data.bytesize + 1 }
+
+        it { expect { subject }.to raise_error('Offset is out of range') }
       end
       context 'when offset is 10' do
         let(:offset) { 10 }
-        it 'appends' do
+        it 'truncates' do
           subject
-          expect(build_trace_chunk.data).to eq(data.byteslice(0, offset) + new_data)
+          expect(build_trace_chunk.data).to eq(data.byteslice(0, offset))
         end
       end
     end
@@ -228,18 +333,29 @@ describe Ci::BuildTraceChunk, :clean_gitlab_redis_shared_state do
       let(:data) { 'Sample data in redis' }
       before do
-        build_trace_chunk.send(:redis_set_data, data)
+        build_trace_chunk.send(:unsafe_set_data!, data)
       end
-      it_behaves_like 'appends'
+      it_behaves_like 'truncates'
     end
     context 'when data_store is database' do
-      let(:data_store) { :db }
-      let(:raw_data) { 'Sample data in db' }
+      let(:data_store) { :database }
+      let(:raw_data) { 'Sample data in database' }
       let(:data) { raw_data }
-      it_behaves_like 'appends'
+      it_behaves_like 'truncates'
+    end
+
+    context 'when data_store is fog' do
+      let(:data_store) { :fog }
+      let(:data) { 'Sample data in fog' }
+
+      before do
+        build_trace_chunk.send(:unsafe_set_data!, data)
+      end
+
+      it_behaves_like 'truncates'
     end
   end
@@ -253,7 +369,7 @@ describe Ci::BuildTraceChunk, :clean_gitlab_redis_shared_state do
         let(:data) { 'Sample data in redis' }
         before do
-          build_trace_chunk.send(:redis_set_data, data)
+          build_trace_chunk.send(:unsafe_set_data!, data)
         end
         it { is_expected.to eq(data.bytesize) }
@@ -265,10 +381,10 @@ describe Ci::BuildTraceChunk, :clean_gitlab_redis_shared_state do
     end
     context 'when data_store is database' do
-      let(:data_store) { :db }
+      let(:data_store) { :database }
       context 'when data exists' do
-        let(:raw_data) { 'Sample data in db' }
+        let(:raw_data) { 'Sample data in database' }
         let(:data) { raw_data }
         it { is_expected.to eq(data.bytesize) }
@@ -278,10 +394,43 @@ describe Ci::BuildTraceChunk, :clean_gitlab_redis_shared_state do
         it { is_expected.to eq(0) }
       end
     end
+
+    context 'when data_store is fog' do
+      let(:data_store) { :fog }
+
+      context 'when data exists' do
+        let(:data) { 'Sample data in fog' }
+        let(:key) { "tmp/builds/#{build.id}/chunks/#{chunk_index}.log" }
+
+        before do
+          build_trace_chunk.send(:unsafe_set_data!, data)
+        end
+
+        it { is_expected.to eq(data.bytesize) }
+      end
+
+      context 'when data does not exist' do
+        it { is_expected.to eq(0) }
+      end
+    end
   end
-  describe '#use_database!' do
-    subject { build_trace_chunk.use_database! }
+  describe '#persist_data!' do
+    subject { build_trace_chunk.persist_data! }
+
+    shared_examples_for 'Atomic operation' do
+      context 'when the other process is persisting' do
+        let(:lease_key) { "trace_write:#{build_trace_chunk.build.id}:chunks:#{build_trace_chunk.chunk_index}" }
+
+        before do
+          stub_exclusive_lease_taken(lease_key)
+        end
+
+        it 'raise an error' do
+          expect { subject }.to raise_error('Failed to obtain a lock')
+        end
+      end
+    end
     context 'when data_store is redis' do
       let(:data_store) { :redis }
@@ -290,46 +439,93 @@ describe Ci::BuildTraceChunk, :clean_gitlab_redis_shared_state do
         let(:data) { 'Sample data in redis' }
         before do
-          build_trace_chunk.send(:redis_set_data, data)
+          build_trace_chunk.send(:unsafe_set_data!, data)
         end
-        it 'stashes the data' do
-          expect(build_trace_chunk.data_store).to eq('redis')
-          expect(build_trace_chunk.send(:redis_data)).to eq(data)
-          expect(build_trace_chunk.raw_data).to be_nil
+        it 'persists the data' do
+          expect(build_trace_chunk.redis?).to be_truthy
+          expect(Ci::BuildTraceChunks::Redis.new.data(build_trace_chunk)).to eq(data)
+          expect(Ci::BuildTraceChunks::Database.new.data(build_trace_chunk)).to be_nil
+          expect { Ci::BuildTraceChunks::Fog.new.data(build_trace_chunk) }.to raise_error(Excon::Error::NotFound)
           subject
-          expect(build_trace_chunk.data_store).to eq('db')
-          expect(build_trace_chunk.send(:redis_data)).to be_nil
-          expect(build_trace_chunk.raw_data).to eq(data)
+          expect(build_trace_chunk.fog?).to be_truthy
+          expect(Ci::BuildTraceChunks::Redis.new.data(build_trace_chunk)).to be_nil
+          expect(Ci::BuildTraceChunks::Database.new.data(build_trace_chunk)).to be_nil
+          expect(Ci::BuildTraceChunks::Fog.new.data(build_trace_chunk)).to eq(data)
         end
+
+        it_behaves_like 'Atomic operation'
       end
       context 'when data does not exist' do
-        it 'does not call UPDATE' do
-          expect(ActiveRecord::QueryRecorder.new { subject }.count).to eq(0)
+        it 'does not persist' do
+          expect { subject }.to raise_error('Can not persist empty data')
         end
       end
     end
     context 'when data_store is database' do
-      let(:data_store) { :db }
-      it 'does not call UPDATE' do
-        expect(ActiveRecord::QueryRecorder.new { subject }.count).to eq(0)
+      let(:data_store) { :database }
+      context 'when data exists' do
+        let(:data) { 'Sample data in database' }
+
+        before do
+          build_trace_chunk.send(:unsafe_set_data!, data)
+        end
+
+        it 'persists the data' do
+          expect(build_trace_chunk.database?).to be_truthy
+          expect(Ci::BuildTraceChunks::Redis.new.data(build_trace_chunk)).to be_nil
+          expect(Ci::BuildTraceChunks::Database.new.data(build_trace_chunk)).to eq(data)
+          expect { Ci::BuildTraceChunks::Fog.new.data(build_trace_chunk) }.to raise_error(Excon::Error::NotFound)
+
+          subject
+
+          expect(build_trace_chunk.fog?).to be_truthy
+          expect(Ci::BuildTraceChunks::Redis.new.data(build_trace_chunk)).to be_nil
+          expect(Ci::BuildTraceChunks::Database.new.data(build_trace_chunk)).to be_nil
+          expect(Ci::BuildTraceChunks::Fog.new.data(build_trace_chunk)).to eq(data)
+        end
+
+        it_behaves_like 'Atomic operation'
       end
-    end
-  end
-  describe 'ExclusiveLock' do
-    before do
-      stub_exclusive_lease_taken
-      stub_const('Ci::BuildTraceChunk::WRITE_LOCK_RETRY', 1)
+      context 'when data does not exist' do
+        it 'does not persist' do
+          expect { subject }.to raise_error('Can not persist empty data')
+        end
+      end
     end
-    it 'raise an error' do
-      expect { build_trace_chunk.append('ABC', 0) }.to raise_error('Failed to obtain write lock')
+    context 'when data_store is fog' do
+      let(:data_store) { :fog }
+
+      context 'when data exists' do
+        let(:data) { 'Sample data in fog' }
+
+        before do
+          build_trace_chunk.send(:unsafe_set_data!, data)
+        end
+
+        it 'does not change data store' do
+          expect(build_trace_chunk.fog?).to be_truthy
+          expect(Ci::BuildTraceChunks::Redis.new.data(build_trace_chunk)).to be_nil
+          expect(Ci::BuildTraceChunks::Database.new.data(build_trace_chunk)).to be_nil
+          expect(Ci::BuildTraceChunks::Fog.new.data(build_trace_chunk)).to eq(data)
+
+          subject
+
+          expect(build_trace_chunk.fog?).to be_truthy
+          expect(Ci::BuildTraceChunks::Redis.new.data(build_trace_chunk)).to be_nil
+          expect(Ci::BuildTraceChunks::Database.new.data(build_trace_chunk)).to be_nil
+          expect(Ci::BuildTraceChunks::Fog.new.data(build_trace_chunk)).to eq(data)
+        end
+
+        it_behaves_like 'Atomic operation'
+      end
     end
   end

spec/models/ci/build_trace_chunks/database_spec.rb

+require 'spec_helper'
+
+describe Ci::BuildTraceChunks::Database do
+  let(:data_store) { described_class.new }
+
+  describe '#available?' do
+    subject { data_store.available? }
+
+    it { is_expected.to be_truthy }
+  end
+
+  describe '#data' do
+    subject { data_store.data(model) }
+
+    context 'when data exists' do
+      let(:model) { create(:ci_build_trace_chunk, :database_with_data, initial_data: 'sample data in database') }
+
+      it 'returns the data' do
+        is_expected.to eq('sample data in database')
+      end
+    end
+
+    context 'when data does not exist' do
+      let(:model) { create(:ci_build_trace_chunk, :database_without_data) }
+
+      it 'returns nil' do
+        is_expected.to be_nil
+      end
+    end
+  end
+
+  describe '#set_data' do
+    subject { data_store.set_data(model, data) }
+
+    let(:data) { 'abc123' }
+
+    context 'when data exists' do
+      let(:model) { create(:ci_build_trace_chunk, :database_with_data, initial_data: 'sample data in database') }
+
+      it 'overwrites data' do
+        expect(data_store.data(model)).to eq('sample data in database')
+
+        subject
+
+        expect(data_store.data(model)).to eq('abc123')
+      end
+    end
+
+    context 'when data does not exist' do
+      let(:model) { create(:ci_build_trace_chunk, :database_without_data) }
+
+      it 'sets new data' do
+        expect(data_store.data(model)).to be_nil
+
+        subject
+
+        expect(data_store.data(model)).to eq('abc123')
+      end
+    end
+  end
+
+  describe '#delete_data' do
+    subject { data_store.delete_data(model) }
+
+    context 'when data exists' do
+      let(:model) { create(:ci_build_trace_chunk, :database_with_data, initial_data: 'sample data in database') }
+
+      it 'deletes data' do
+        expect(data_store.data(model)).to eq('sample data in database')
+
+        subject
+
+        expect(data_store.data(model)).to be_nil
+      end
+    end
+
+    context 'when data does not exist' do
+      let(:model) { create(:ci_build_trace_chunk, :database_without_data) }
+
+      it 'does nothing' do
+        expect(data_store.data(model)).to be_nil
+
+        subject
+
+        expect(data_store.data(model)).to be_nil
+      end
+    end
+  end
+
+  describe '#keys' do
+    subject { data_store.keys(relation) }
+
+    let(:build) { create(:ci_build) }
+    let(:relation) { build.trace_chunks }
+
+    before do
+      create(:ci_build_trace_chunk, :database_with_data, chunk_index: 0, build: build)
+      create(:ci_build_trace_chunk, :database_with_data, chunk_index: 1, build: build)
+    end
+
+    it 'returns empty array' do
+      is_expected.to eq([])
+    end
+  end
+end

spec/models/ci/build_trace_chunks/fog_spec.rb

+require 'spec_helper'
+
+describe Ci::BuildTraceChunks::Fog do
+  let(:data_store) { described_class.new }
+
+  before do
+    stub_artifacts_object_storage
+  end
+
+  describe '#available?' do
+    subject { data_store.available? }
+
+    context 'when object storage is enabled' do
+      it { is_expected.to be_truthy }
+    end
+
+    context 'when object storage is disabled' do
+      before do
+        stub_artifacts_object_storage(enabled: false)
+      end
+
+      it { is_expected.to be_falsy }
+    end
+  end
+
+  describe '#data' do
+    subject { data_store.data(model) }
+
+    context 'when data exists' do
+      let(:model) { create(:ci_build_trace_chunk, :fog_with_data, initial_data: 'sample data in fog') }
+
+      it 'returns the data' do
+        is_expected.to eq('sample data in fog')
+      end
+    end
+
+    context 'when data does not exist' do
+      let(:model) { create(:ci_build_trace_chunk, :fog_without_data) }
+
+      it 'returns nil' do
+        expect { data_store.data(model) }.to raise_error(Excon::Error::NotFound)
+      end
+    end
+  end
+
+  describe '#set_data' do
+    subject { data_store.set_data(model, data) }
+
+    let(:data) { 'abc123' }
+
+    context 'when data exists' do
+      let(:model) { create(:ci_build_trace_chunk, :fog_with_data, initial_data: 'sample data in fog') }
+
+      it 'overwrites data' do
+        expect(data_store.data(model)).to eq('sample data in fog')
+
+        subject
+
+        expect(data_store.data(model)).to eq('abc123')
+      end
+    end
+
+    context 'when data does not exist' do
+      let(:model) { create(:ci_build_trace_chunk, :fog_without_data) }
+
+      it 'sets new data' do
+        expect { data_store.data(model) }.to raise_error(Excon::Error::NotFound)
+
+        subject
+
+        expect(data_store.data(model)).to eq('abc123')
+      end
+    end
+  end
+
+  describe '#delete_data' do
+    subject { data_store.delete_data(model) }
+
+    context 'when data exists' do
+      let(:model) { create(:ci_build_trace_chunk, :fog_with_data, initial_data: 'sample data in fog') }
+
+      it 'deletes data' do
+        expect(data_store.data(model)).to eq('sample data in fog')
+
+        subject
+
+        expect { data_store.data(model) }.to raise_error(Excon::Error::NotFound)
+      end
+    end
+
+    context 'when data does not exist' do
+      let(:model) { create(:ci_build_trace_chunk, :fog_without_data) }
+
+      it 'does nothing' do
+        expect { data_store.data(model) }.to raise_error(Excon::Error::NotFound)
+
+        subject
+
+        expect { data_store.data(model) }.to raise_error(Excon::Error::NotFound)
+      end
+    end
+  end
+
+  describe '#keys' do
+    subject { data_store.keys(relation) }
+
+    let(:build) { create(:ci_build) }
+    let(:relation) { build.trace_chunks }
+
+    before do
+      create(:ci_build_trace_chunk, :fog_with_data, chunk_index: 0, build: build)
+      create(:ci_build_trace_chunk, :fog_with_data, chunk_index: 1, build: build)
+    end
+
+    it 'returns keys' do
+      is_expected.to eq([[build.id, 0], [build.id, 1]])
+    end
+  end
+
+  describe '#delete_keys' do
+    subject { data_store.delete_keys(keys) }
+
+    let(:build) { create(:ci_build) }
+    let(:relation) { build.trace_chunks }
+    let(:keys) { data_store.keys(relation) }
+
+    before do
+      create(:ci_build_trace_chunk, :fog_with_data, chunk_index: 0, build: build)
+      create(:ci_build_trace_chunk, :fog_with_data, chunk_index: 1, build: build)
+    end
+
+    it 'deletes multiple data' do
+      ::Fog::Storage.new(JobArtifactUploader.object_store_credentials).tap do |connection|
+        expect(connection.get_object('artifacts', "tmp/builds/#{build.id}/chunks/0.log")[:body]).to be_present
+        expect(connection.get_object('artifacts', "tmp/builds/#{build.id}/chunks/1.log")[:body]).to be_present
+      end
+
+      subject
+
+      ::Fog::Storage.new(JobArtifactUploader.object_store_credentials).tap do |connection|
+        expect { connection.get_object('artifacts', "tmp/builds/#{build.id}/chunks/0.log")[:body] }.to raise_error(Excon::Error::NotFound)
+        expect { connection.get_object('artifacts', "tmp/builds/#{build.id}/chunks/1.log")[:body] }.to raise_error(Excon::Error::NotFound)
+      end
+    end
+  end
+end

spec/models/ci/build_trace_chunks/redis_spec.rb

+require 'spec_helper'
+
+describe Ci::BuildTraceChunks::Redis, :clean_gitlab_redis_shared_state do
+  let(:data_store) { described_class.new }
+
+  describe '#available?' do
+    subject { data_store.available? }
+
+    it { is_expected.to be_truthy }
+  end
+
+  describe '#data' do
+    subject { data_store.data(model) }
+
+    context 'when data exists' do
+      let(:model) { create(:ci_build_trace_chunk, :redis_with_data, initial_data: 'sample data in redis') }
+
+      it 'returns the data' do
+        is_expected.to eq('sample data in redis')
+      end
+    end
+
+    context 'when data does not exist' do
+      let(:model) { create(:ci_build_trace_chunk, :redis_without_data) }
+
+      it 'returns nil' do
+        is_expected.to be_nil
+      end
+    end
+  end
+
+  describe '#set_data' do
+    subject { data_store.set_data(model, data) }
+
+    let(:data) { 'abc123' }
+
+    context 'when data exists' do
+      let(:model) { create(:ci_build_trace_chunk, :redis_with_data, initial_data: 'sample data in redis') }
+
+      it 'overwrites data' do
+        expect(data_store.data(model)).to eq('sample data in redis')
+
+        subject
+
+        expect(data_store.data(model)).to eq('abc123')
+      end
+    end
+
+    context 'when data does not exist' do
+      let(:model) { create(:ci_build_trace_chunk, :redis_without_data) }
+
+      it 'sets new data' do
+        expect(data_store.data(model)).to be_nil
+
+        subject
+
+        expect(data_store.data(model)).to eq('abc123')
+      end
+    end
+  end
+
+  describe '#delete_data' do
+    subject { data_store.delete_data(model) }
+
+    context 'when data exists' do
+      let(:model) { create(:ci_build_trace_chunk, :redis_with_data, initial_data: 'sample data in redis') }
+
+      it 'deletes data' do
+        expect(data_store.data(model)).to eq('sample data in redis')
+
+        subject
+
+        expect(data_store.data(model)).to be_nil
+      end
+    end
+
+    context 'when data does not exist' do
+      let(:model) { create(:ci_build_trace_chunk, :redis_without_data) }
+
+      it 'does nothing' do
+        expect(data_store.data(model)).to be_nil
+
+        subject
+
+        expect(data_store.data(model)).to be_nil
+      end
+    end
+  end
+
+  describe '#keys' do
+    subject { data_store.keys(relation) }
+
+    let(:build) { create(:ci_build) }
+    let(:relation) { build.trace_chunks }
+
+    before do
+      create(:ci_build_trace_chunk, :redis_with_data, chunk_index: 0, build: build)
+      create(:ci_build_trace_chunk, :redis_with_data, chunk_index: 1, build: build)
+    end
+
+    it 'returns keys' do
+      is_expected.to eq([[build.id, 0], [build.id, 1]])
+    end
+  end
+
+  describe '#delete_keys' do
+    subject { data_store.delete_keys(keys) }
+
+    let(:build) { create(:ci_build) }
+    let(:relation) { build.trace_chunks }
+    let(:keys) { data_store.keys(relation) }
+
+    before do
+      create(:ci_build_trace_chunk, :redis_with_data, chunk_index: 0, build: build)
+      create(:ci_build_trace_chunk, :redis_with_data, chunk_index: 1, build: build)
+    end
+
+    it 'deletes multiple data' do
+      Gitlab::Redis::SharedState.with do |redis|
+        expect(redis.exists("gitlab:ci:trace:#{build.id}:chunks:0")).to be_truthy
+        expect(redis.exists("gitlab:ci:trace:#{build.id}:chunks:1")).to be_truthy
+      end
+
+      subject
+
+      Gitlab::Redis::SharedState.with do |redis|
+        expect(redis.exists("gitlab:ci:trace:#{build.id}:chunks:0")).to be_falsy
+        expect(redis.exists("gitlab:ci:trace:#{build.id}:chunks:1")).to be_falsy
+      end
+    end
+  end
+end

spec/support/helpers/stub_object_storage.rb

@@ -25,6 +25,11 @@ module StubObjectStorage
     ::Fog::Storage.new(connection_params).tap do |connection|
       begin
         connection.directories.create(key: remote_directory)
+
+        # Cleanup remaining files
+        connection.directories.each do |directory|
+          directory.files.map(&:destroy)
+        end
       rescue Excon::Error::Conflict
       end
     end