Format Unicorn log timestamps

- to be in UTC
- and to be in ISO8601 format with seconds upto
3 fractional digits

config/unicorn.rb.example

@@ -82,6 +82,7 @@ preload_app true
 check_client_connection false
 
 require_relative "/home/git/gitlab/lib/gitlab/cluster/lifecycle_events"
+require_relative "/home/git/gitlab/lib/gitlab/log_timestamp_formatter.rb"
 
 before_exec do |server|
   # Signal application hooks that we're about to restart
@@ -137,3 +138,7 @@ after_fork do |server, worker|
   # addr = "127.0.0.1:#{9293 + worker.nr}"
   # server.listen(addr, :tries => -1, :delay => 5, :tcp_nopush => true)
 end
+
+# Configure the default logger to use a custom formatter that formats the
+# timestamps to be in UTC and in ISO8601.3 format
+Configurator::DEFAULTS[:logger].formatter = Gitlab::LogTimestampFormatter.new

config/unicorn.rb.example.development

@@ -15,6 +15,7 @@ preload_app true
 check_client_connection false
 
 require_relative "/home/git/gitlab/lib/gitlab/cluster/lifecycle_events"
+require_relative "/home/git/gitlab/lib/gitlab/log_timestamp_formatter.rb"
 
 before_exec do |server|
   # Signal application hooks that we're about to restart
@@ -70,3 +71,7 @@ after_fork do |server, worker|
   # addr = "127.0.0.1:#{9293 + worker.nr}"
   # server.listen(addr, :tries => -1, :delay => 5, :tcp_nopush => true)
 end
+
+# Configure the default logger to use a custom formatter that formats the
+# timestamps to be in UTC and in ISO8601.3 format
+Configurator::DEFAULTS[:logger].formatter = Gitlab::LogTimestampFormatter.new

lib/gitlab/log_timestamp_formatter.rb

+# frozen_string_literal: true
+
+module Gitlab
+  class LogTimestampFormatter < Logger::Formatter
+    FORMAT = "%s, [%s #%d] %5s -- %s: %s\n"
+
+    def call(severity, timestamp, program_name, message)
+      FORMAT % [severity[0..0], timestamp.utc.iso8601(3), $$, severity, program_name, msg2str(message)]
+    end
+  end
+end

spec/lib/gitlab/log_timestamp_formatter_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::LogTimestampFormatter do
+  subject { described_class.new }
+
+  let(:formatted_timestamp) { Time.now.utc.iso8601(3) }
+
+  it 'logs the timestamp in UTC and ISO8601.3 format' do
+    Timecop.freeze(Time.now) do
+      expect(subject.call('', Time.now, '', '')).to include formatted_timestamp
+    end
+  end
+end