Merge pull request #5 from instana/fix_forking_webservers

Ruby Sensor not detecting/handling forking webservers correctly

Author: pglombardo

lib/instana/agent.rb

@@ -22,6 +22,9 @@ def initialize
       # Supported two states (unannounced & announced)
       @state = :unannounced
 
+      # Store the pid from process boot so we can detect forks
+      @pid = Process.pid
+
       # Snapshot data is collected once per process but resent
       # every 10 minutes along side process metrics.
       @snapshot = take_snapshot
@@ -39,8 +42,9 @@ def initialize
       @announce_timer = nil
       @collect_timer = nil
 
-      # Detect if we're on linux or not (used in host_agent_ready?)
+      # Detect platform flags
       @is_linux = (RUBY_PLATFORM =~ /linux/i) ? true : false
+      @is_osx = (RUBY_PLATFORM =~ /darwin/i) ? true : false
 
       # In case we're running in Docker, have the default gateway available
       # to check in case we're running in bridged network mode
@@ -53,23 +57,68 @@ def initialize
       # The agent UUID returned from the host agent
       @agent_uuid = nil
 
+      collect_process_info
+    end
+
+    # Used in class initialization and after a fork, this method
+    # collects up process information and stores it in @process
+    #
+    def collect_process_info
       @process = {}
       cmdline = ProcTable.ps(Process.pid).cmdline.split("\0")
       @process[:name] = cmdline.shift
       @process[:arguments] = cmdline
-      @process[:original_pid] = Process.pid
+
+      if @is_osx
+        # Handle OSX bug where env vars show up at the end of process name
+        # such as MANPATH etc..
+        @process[:name].gsub!(/[_A-Z]+=\S+/, '')
+        @process[:name].rstrip!
+      end
+
+      @process[:original_pid] = @pid
       # This is usually Process.pid but in the case of docker, the host agent
       # will return to us the true host pid in which we use to report data.
       @process[:report_pid] = nil
     end
 
+    # Determine whether the pid has changed since Agent start.
+    #
+    # @ return [Boolean] true or false to indicate if forked
+    #
+    def forked?
+      @pid != Process.pid
+    end
+
+    # Used post fork to re-initialize state and restart communications with
+    # the host agent.
+    #
+    def after_fork
+      ::Instana.logger.debug "after_fork hook called. Falling back to unannounced state."
+
+      # Re-collect process information post fork
+      @pid = Process.pid
+      collect_process_info
+
+      # Set last snapshot to 10 minutes ago
+      # so we send a snapshot sooner than later
+      @last_snapshot = Time.now - 600
+
+      transition_to(:unannounced)
+      start
+    end
+
     # Sets up periodic timers and starts the agent in a background thread.
     #
     def start
       # The announce timer
       # We attempt to announce this ruby sensor to the host agent.
       # In case of failure, we try again in 30 seconds.
       @announce_timer = @timers.now_and_every(30) do
+        if forked?
+          after_fork
+          break
+        end
         if host_agent_ready? && announce_sensor
           ::Instana.logger.debug "Announce successful. Switching to metrics collection."
           transition_to(:announced)
@@ -81,6 +130,10 @@ def start
       # every ::Instana::Collector.interval seconds.
       @collect_timer = @timers.every(::Instana::Collector.interval) do
         if @state == :announced
+          if forked?
+            after_fork
+            break
+          end
           unless ::Instana::Collector.collect_and_report
             # If report has been failing for more than 1 minute,
             # fall back to unannounced state

lib/instana/instrumentation/rack.rb

@@ -27,19 +27,21 @@ def call(env)
 
       status, headers, response = @app.call(env)
 
-      kvs[:http][:status] = status
+      if ::Instana.tracer.tracing?
+        kvs[:http][:status] = status
 
-      # Save the IDs before the trace ends so we can place
-      # them in the response headers in the ensure block
-      trace_id = ::Instana.tracer.trace_id
-      span_id = ::Instana.tracer.span_id
+        # Save the IDs before the trace ends so we can place
+        # them in the response headers in the ensure block
+        trace_id = ::Instana.tracer.trace_id
+        span_id = ::Instana.tracer.span_id
+      end
 
       [status, headers, response]
     rescue Exception => e
       ::Instana.tracer.log_error(e)
       raise
     ensure
-      if headers
+      if headers && ::Instana.tracer.tracing?
         # Set reponse headers; encode as hex string
         headers['X-Instana-T'] = ::Instana.tracer.id_to_header(trace_id)
         headers['X-Instana-S'] = ::Instana.tracer.id_to_header(span_id)

test/tracing/trace_test.rb

@@ -24,7 +24,7 @@ def test_max_value_of_generated_id
     # Max is the maximum value for a Java signed long
     max_value = 9223372036854775807
     100.times do
-      assert t.send(:generate_id) < max_value
+      assert t.send(:generate_id) <= max_value
     end
   end
 end