Remove the rewiring stdout and strerr logic

The redirection was a workaround for log file parsers and
it is no longer needed. So we remove that part and simplify the logger settings.

Co-authored-by: Neamah Al-Selwi <neamah.alselwi@digital.cabinet-office.gov.uk>
Co-authored-by: Tuomas Nylund <tuomas.nylund@digital.cabinet-office.gov.uk>

README.md

@@ -142,9 +142,6 @@ check docs](docs/healthchecks.md) for more information on how to use it.
 
 ## Rails logging
 
-In Rails applications, the application will be configured to send JSON-formatted
-logs to `STDOUT` and unstructured logs to `STDERR`.
-
 To enable production-like logging, an env variable `GOVUK_RAILS_JSON_LOGGING`
 is set in the `govuk-helm-charts` and then checked in `railtie.rb`. This will
 allow JSON format logs and `Govuk-Request-Id` to be visible.

lib/govuk_app_config/govuk_json_logging.rb

@@ -5,32 +5,14 @@
 
 module GovukJsonLogging
   def self.configure
-    # GOV.UK Rails applications are expected to output JSON to stdout which is
-    # then indexed in a Kibana instance. These log outputs are created by the
-    # logstasher gem.
-    #
-    # Rails applications will typically write other things to stdout such as
-    # `Rails.logger` calls or 'puts' statements. However these are not in a
-    # JSON format which causes problems for the log file parsers.
-    #
-    # To resolve this we redirect stdout to stderr, to cover any Rails
-    # writing. This frees up the normal stdout for the logstasher logs.
-    #
     # We also disable buffering, so that logs aren't lost on crash or delayed
     # indefinitely while troubleshooting.
-
-    # rubocop:disable Style/GlobalVars
-    $real_stdout = $stdout.clone
-    $real_stdout.sync = true
-    $stdout.reopen($stderr)
     $stdout.sync = true
-    # rubocop:enable Style/GlobalVars
 
     Rails.logger = Logger.new(
-      $real_stdout, # rubocop:disable Style/GlobalVars
+      $stdout,
       level: Rails.logger.level,
       formatter: proc { |severity, datetime, _progname, msg|
-
         begin
           message = JSON.parse(msg)
         rescue JSON::ParserError, TypeError => _e
@@ -77,7 +59,7 @@ def self.configure
     Rails.application.config.logstasher.source = {}
 
     Rails.application.config.logstasher.logger = Logger.new(
-      $real_stdout, # rubocop:disable Style/GlobalVars
+      $stdout,
       level: Rails.logger.level,
       formatter: proc { |_severity, _datetime, _progname, msg|
         "#{msg.is_a?(String) ? msg : msg.inspect}\n"

spec/lib/govuk_json_logging_spec.rb

@@ -23,22 +23,23 @@ def self.headers
   after { Rails.application = nil }
 
   original_stderr = nil
+  original_stdout = nil
 
   let(:fake_stdout) { StringIO.new }
   let(:fake_stderr) { StringIO.new }
   let(:info_log_level) { 1 }
 
   before do
     original_stderr = $stderr
+    original_stdout = $stdout
     $stderr = fake_stderr
-    allow($stdout).to receive(:clone).and_return(fake_stdout)
-    allow($stdout).to receive(:reopen)
+    $stdout = fake_stdout
     Rails.logger = Logger.new(fake_stdout, level: info_log_level)
-
   end
 
   after do
     $stderr = original_stderr
+    $stdout = original_stdout
   end
 
   describe ".configure" do
@@ -80,7 +81,7 @@ def app
         Rails.application
       end
 
-      it "logs errors thrown by the application" do
+      it "logs errors thrown by the application with govuk_request_id" do
         stub_const("GdsApi::GovukHeaders", govuk_headers_class)
         GovukJsonLogging.configure
         get "/error"
@@ -133,7 +134,6 @@ def app
 
         expect(log_json).to include("message" => "test default log entry")
         expect(log_json).to include("govuk_request_id" => "some-value")
-
       end
     end
   end