Correlating requests with a method invoked later in the call stack for new integration

[rombert]

Hi,

I am working on adding support for Apache Sling to Open Telemetry. Sling is a Java-based web application framework, and the first item on my list is to customize the span name to reflect the handler.

Sling embeds Jetty has a well-defined entry point in the so-called SlingMainServlet, so what OTEL initially seems is a mapping for /*.

When Sling handlers a request it has a service entry point method, but associating a request with a "handler" (servlet resolution in Sling jargon → ServletResolver ) happens much later in the stack. I can't "just" instrument the servlet resolution because when handling a request in Sling there is usually a top-level servlet and multiple 'child' servlets which compose the result.

I have two rough ideas right now:

• "mark" the top-level request as it arrives in the SlingMainServlet and instrument the span name during servlet resolution if the request is a top-level one. I could set a well-known request attribute and read it down the line.
• use a thread-local in the ServletResolver to see if it has been invoked already ; but since I don't have a good way of cleaning up without tracking request lifecycle

Does any of these ideas sound workable form an OTEL point of view? Are there any other patters in the java library that could be useful in my scenario?

Thanks!

[laurit]

When you just want to update the server span name then usually we use

opentelemetry-java-instrumentation/instrumentation/play/play-mvc/play-mvc-2.6/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/play/v2_6/Play26Singletons.java

Line 63 in db7eb14

HttpServerRoute.update(context, HttpServerRouteSource.CONTROLLER, route);

Set route source to CONTROLLER to overwrite the value from the servlet instrumentation or NESTED_CONTROLLER like in

opentelemetry-java-instrumentation/instrumentation/jaxrs/jaxrs-2.0/jaxrs-2.0-jersey-2.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/jaxrs/v2_0/JerseySpanName.java

Line 28 in db7eb14

HttpServerRoute.update(context, HttpServerRouteSource.NESTED_CONTROLLER, this, request);

to overwrite all previous values.

[rombert]

Thanks @laurit . By briefly looking at the code and also via testing, it seems that when I use the following snippet the first call for a given span is used for the update and the rest are ignored.

HttpServerRoute.update(context, HttpServerRouteSource.CONTROLLER, route); 

Is that correct? If it is, it would greatly simplify the work I would need to do.

[trask]

it seems that when I use the following snippet the first call for a given span is used for the update and the rest are ignored

yes, the HttpServerRoute only updates the span name and http.route attribute the top-most SERVER span

[rombert]

Great, thanks for confirming @trask .