Product observability enables rapid debugging of product issues. The ESB profile of WSO2 Enterprise Integrator (WSO2 EI) enables observability using correlation logs. Correlation logs allow you to monitor individual HTTP requests from the point that a message is received by the ESB until the corresponding response message is sent back to the original message sender. That is, the complete round trip of an HTTP message (client → ESB → back-end → ESB → client) can be tracked and anlyzed using a log file.
When correlation logs are enabled for the ESB server, a separate log file named correlation.log is created in the <EI_HOME>/repository/logs/ directory. Every HTTP message that flows through the ESB and between the ESB and external clients undergoes several state changes. A new log entry is created in the correlation.log file corresponding to the state changes in the round trip of a single HTTP request. A correlation ID assigned to the incoming HTTP request is assigned to all the log entries corresponding to the request. Therefore, you can use this correlation ID to easily locate the logs relevant to the round trip of a specific HTTP request and, thereby, analyze the behaviour of the message flow.
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To use this feature in the current version of WSO2 EI, you need to get the latest product updates for your product. This feature is available as a product update from 2018-11-24 onwards.
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When the client sends an HTTP request to the ESB, a correlation ID for the request can be passed using the correlation header. By default, the correlation header is 'activity_idactivityid'. If you want to change the default correlation header, see the topic on configuring correlation logs. If the client does not pass a correlation ID in the request, the ESB will generate an internal value and assign it to the request. The correlation ID assigned to the incoming request is assigned to all the log entries that are related to the same request.
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