track failed probes

lib/datadog/di/error.rb

@@ -26,6 +26,12 @@ class AgentCommunicationError < Error
       # that does not in fact exist anywhere (e.g. due to a misspelling).
       class DITargetNotDefined < Error
       end
+
+      # Raised when trying to install a probe whose installation failed
+      # earlier in the same process. This exception should contain the
+      # original exception report from initial installation attempt.
+      class ProbePreviouslyFailed < Error
+      end
     end
   end
 end

lib/datadog/di/probe_manager.rb

@@ -20,6 +20,7 @@ def initialize(settings, instrumenter, probe_notification_builder,
         @logger = logger
         @installed_probes = {}
         @pending_probes = {}
+        @failed_probes = {}
 
         @definition_trace_point = TracePoint.trace(:end) do |tp|
           begin
@@ -56,9 +57,21 @@ def clear_hooks
       attr_reader :installed_probes
       attr_reader :pending_probes
 
+      # Probes that failed to instrument for reasons other than the target is
+      # not yet loaded are added to this collection, so that we do not try
+      # to instrument them every time remote configuration is processed.
+      attr_reader :failed_probes
+
       # config is one probe info
       def add_probe(probe)
         # TODO lock here?
+
+        # Probe failed to install previously, do not try to install it again.
+        if msg = failed_probes[probe.id]
+          # TODO test this path
+          raise Error::ProbePreviouslyFailed, msg
+        end
+
         begin
           instrumenter.hook(probe, &method(:probe_executed_callback))
 
@@ -76,11 +89,17 @@ def add_probe(probe)
           false
         end
       rescue => exc
+        # In "propagate all exceptions" mode we will try to instrument again.
         raise if settings.dynamic_instrumentation.internal.propagate_all_exceptions
-        # Silence all exceptions?
-        # TODO should we propagate here and rescue upstream?
+
         logger.warn("Error processing probe configuration: #{exc.class}: #{exc}")
-        nil
+        # TODO report probe as failed to agent since we won't attempt to
+        # install it again.
+
+        # TODO add top stack frame to message
+        failed_probes[probe.id] = "#{exc.class}: #{exc}"
+
+        raise
       end
 
       def remove_other_probes(probe_ids)

lib/datadog/di/remote.rb

@@ -59,6 +59,12 @@ def receivers(telemetry)
 
                     component.logger.warn("Unhandled exception adding probe in DI remote receiver: #{e.class}: #{e}")
 
+                    # If a probe fails to install, we will mark the content
+                    # as errored. On subsequent remote configuration application
+                    # attemps, probe manager will raise the "previously errored"
+                    # exception and we'll rescue it here, again marking the
+                    # content as errored but with a somewhat different exception
+                    # message.
                     content.errored("Error applying dynamic instrumentation configuration: #{e.class.name} #{e.message}: #{Array(e.backtrace).join("\n")}")
                   end
 

spec/datadog/di/probe_manager_spec.rb

@@ -66,6 +66,7 @@ class ProbeManagerSpecTestClass; end
           expect(manager.add_probe(probe)).to be true
 
           expect(manager.pending_probes.length).to eq 0
+          expect(manager.failed_probes.length).to eq 0
 
           expect(manager.installed_probes.length).to eq 1
           expect(manager.installed_probes["3ecfd456-2d7c-4359-a51f-d4cc44141ffe"]).to be(probe)
@@ -88,11 +89,12 @@ class ProbeManagerSpecTestClass; end
           expect(manager.pending_probes["3ecfd456-2d7c-4359-a51f-d4cc44141ffe"]).to be(probe)
 
           expect(manager.installed_probes.length).to eq 0
+          expect(manager.failed_probes.length).to eq 0
         end
       end
 
       context 'when there is an exception during instrumentation' do
-        it 'returns nil, logs warning and drops probe' do
+        it 'logs warning, drops probe and reraises the exception' do
           expect(logger).to receive(:warn) do |msg|
             expect(msg).to match(/Error processing probe configuration.*Instrumentation error/)
           end
@@ -105,11 +107,16 @@ class ProbeManagerSpecTestClass; end
           expect(probe_notification_builder).not_to receive(:build_installed)
           expect(probe_notifier_worker).not_to receive(:add_status)
 
-          expect(manager.add_probe(probe)).to be nil
+          expect do
+            manager.add_probe(probe)
+          end.to raise_error(RuntimeError, 'Instrumentation error')
 
           expect(manager.pending_probes.length).to eq 0
 
           expect(manager.installed_probes.length).to eq 0
+
+          expect(manager.failed_probes.length).to eq 1
+          expect(manager.failed_probes[probe.id]).to match(/Instrumentation error/)
         end
       end
     end