Product observability enables rapid debugging of product issues. The WSO2 Enterprise Service Bus (ESB) 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
<ESB_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.
To use this feature in the current version of WSO2 ESB, you need to get the latest product updates for your product. This feature is available as a product update from 2019-01-04 onwards.
Note that you can deploy updates in a production environment only if you have a valid subscription with WSO2. Read more about WSO2 Updates.
See the following topics for details:
Configuring correlation logs
Follow the steps given below to configure correlation logs in the ESB server.
Add the following parameters to the
log4j.propertiesfile (stored in the
Note that the maximum file size of the correlation log is set to 10MB in the above configuration. That is, when the size of the file exceeds 10MB, a new log file is created. If required, you can change this file size.
If required, you can change the default HTTP header (which is 'activity_id') that is used to carry the correlation ID by adding the following property to the
passthru-http.propertiesfile (stored in the
<correlation_id>with a value of your choice.
Once the logs are configured, correlation logging should be enabled in the ESB as explained in the next section.
Enabling correlation logs in the ESB
You can enable correlation logging by passing a system property.
If you want correlation logs to be enabled every time the server starts, add the following system property to the product start-up script (stored in the
<ESB_HOME>/bin/directory) and set it to
Alternatively, you can pass the system property at the time of starting the server by executing the following command:
Now when you start the ESB server, the
correlation.log file is created in the
Sending an HTTP request with a correlation ID
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 'activityid'. 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.
Shown below is the POST request that is sent using the CURL client. Note that the correlation ID is set in this request.
Accessing the correlation logs
If you know the correlation ID of the HTTP request that you want to analyze, you can isolate the relevant logs as explained below.
- Open a terminal and navigate to the
<ESB_HOME>/repository/logs/directory where the
correlation.logfile is saved.
Execute the following command with the required correlation ID. Replace <correlation_ID> with the required value.
Shown below is an example of correlation log entries corresponding to the round trip of a single HTTP request.
Reading correlation logs
The pattern/format of a correlation log is shown below along with an example log entry.
The detail recorded in a log entry is described below.
The time at which the log is created.
Each log contains a correlation ID, which is unique to the HTTP request. A client can send the correlation ID in the header of the HTTP request. If this correlation ID is missing in the incoming request, the ESB will generate one for the request.
The HTTP header that carries the correlation ID is configured in the ESB.
The identifier of the thread.
The duration (given in milliseconds) depends on the type of log entry:
There are two possible call types:
This is a name that is generated to identify the connection between the ESB and the external client.
The HTTP method used for the request.
The connection URL of the external client with which the message is being communicated. For example, if the message is being read from the client, the connection URL corresponds to the client sending the message. However, if the message is being written to the backend, the URL corresponds to the backend client.
Listed below are the state changes that a message goes through when it flows through the ESB, and when the message flows between the ESB and external clients. Typically, a new log entry is generated for each of the states. However, there can be two separate log entries created for one particular state (except for BACKEND LATENCY and ROUND-TRIP LATENCY) depending on whether the message is being read (from the sender) or written (to the backend). You can identify the two separate log entries from the connection URL explained above.