Use standard timestamp format for application logs

changelogs/unreleased/standardize-timestamp-format-in-app-logs.yml

+---
+title: 'Use IS08601.3 format for app level logging of timestamps'
+merge_request: 22793
+author:
+type: other

doc/development/logging.md

@@ -191,7 +191,7 @@ Here are some examples of how messages would be handled by both the loggers.
 FancyMultiLogger.info("Information")
 
 # UnstructuredLogger
-I, [2020-01-13T12:02:41.566219 #6652]  INFO -- : Information
+I, [2020-01-13T18:48:49.201Z #5647]  INFO -- : Information
 
 # StructuredLogger
 {:severity=>"INFO", :time=>"2020-01-13T11:02:41.559Z", :correlation_id=>"b1701f7ecc4be4bcd4c2d123b214e65a", :message=>"Information"}
@@ -203,7 +203,7 @@ I, [2020-01-13T12:02:41.566219 #6652]  INFO -- : Information
 FancyMultiLogger.info({:message=>"This is my message", :project_id=>123})
 
 # UnstructuredLogger
-I, [2020-01-13T12:06:09.856766 #8049]  INFO -- : {:message=>"This is my message", :project_id=>123}
+I, [2020-01-13T19:01:17.091Z #11056]  INFO -- : {"message"=>"Message", "project_id"=>"123"}
 
 # StructuredLogger
 {:severity=>"INFO", :time=>"2020-01-13T11:06:09.851Z", :correlation_id=>"d7e0886f096db9a8526a4f89da0e45f6", :message=>"This is my message", :project_id=>123}

lib/gitlab/app_text_logger.rb

@@ -7,7 +7,7 @@ module Gitlab
     end
 
     def format_message(severity, timestamp, progname, msg)
-      "#{timestamp.to_s(:long)}: #{msg}\n"
+      "#{timestamp.utc.iso8601(3)}: #{msg}\n"
     end
   end
 end

spec/lib/gitlab/app_text_logger_spec.rb

@@ -15,4 +15,11 @@ describe Gitlab::AppTextLogger do
   it 'logs a string unchanged' do
     expect(subject.format_message('INFO', Time.now, nil, string_message)).to include(string_message)
   end
+
+  it 'logs time in UTC with ISO8601.3 standard' do
+    Timecop.freeze do
+      expect(subject.format_message('INFO', Time.now, nil, string_message))
+        .to include(Time.now.utc.iso8601(3))
+    end
+  end
 end