This article describes one possible warning message that might be found in the log of an Enterprise Manager, and explains why it occurs
What do the warning messages "[Manager] AgentThresholdDeliveryService: unable to get trigger service for agent" mean, and why do they occur ?
Any supported environment running Application Performance Management
All pre-APM-10 agents cause those messages to appear in the logs upon EM restart. The messages are logged when an agent connects to an Enterprise Manager and is caused by the Differential Analysis feature (which triggers a trace when application abnormalities are found), and the fact that agents prior to APM10 does not have that feature. During initialization of an agent connection, the Differential Analysis feature tries to link up with the agent to be able to trigger traces, but in pre-APM10 agents, since the feature wasn't available, the "trigger" messages are logged.
The messages weren't masked or set to a higher logging level (like VERBOSE or DEBUG) because if they were masked or the logging level changed, then messages about failures of APM10 agents to connect to the DA service would also be masked/hidden.