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Remove outdated info from servlet README.md (#5903)

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Lauri Tulmin 2022-04-21 18:55:30 +03:00 committed by GitHub
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@ -13,20 +13,13 @@ We support Servlet API starting from version 2.2.
But various instrumentations apply to different versions of the API. But various instrumentations apply to different versions of the API.
They are divided into the following sub-modules: They are divided into the following sub-modules:
- `servlet-common` contains shared code for both `javax.servlet` and `jakarta.servlet` packages - `servlet-common` contains shared code for both `javax.servlet` and `jakarta.servlet` packages.
- `library` contains the abstract tracer applicable to all servlet versions given an - Version-specific modules contain the version-specific instrumentations and request/response
implementation of `ServletAccessor` to access request and response objects of the specific accessor.
version - `servlet-javax-common` contains instrumentations common for Servlet API versions `[2.2, 5)`
- `javaagent` contains shared type instrumentations which can be used by version specific modules - `servlet-2.2` contains instrumentation for Servlet API versions `[2.2, 3)`
by specifying the base package and advice class to use with them. Contains some helper classes - `servlet-3.0` contains instrumentation for Servlet API versions `[3.0, 5)`
used by advices to reduce code duplication. It does not define any instrumentation modules and - `servlet-5.0` contains instrumentation for Servlet API versions `[5,)`
is used only as a dependency for other `javaagent` modules.
- Version-specific modules where `library` contains the version-specific tracer and request/response
accessor, and `javaagent` contains the instrumentation modules and advices.
- `servlet-javax-common` contains instrumentations/abstract tracer common for Servlet API versions `[2.2, 5)`
- `servlet-2.2` contains instrumentations/tracer for Servlet API versions `[2.2, 3)`
- `servlet-3.0` contains instrumentations/tracer for Servlet API versions `[3.0, 5)`
- `servlet-5.0` contains instrumentations/tracer for Servlet API versions `[5,)`
## Implementation details ## Implementation details
@ -72,14 +65,15 @@ At last, request processing may reach the specific framework that your applicati
In this case Spring MVC and `OwnerController.initCreationForm`. In this case Spring MVC and `OwnerController.initCreationForm`.
If all instrumentations are enabled, then a new span will be created for every highlighted frame. If all instrumentations are enabled, then a new span will be created for every highlighted frame.
All spans from Servlet API will have `kind=SERVER` and name based on corresponding class and method names, All spans from Servlet API will have `kind=SERVER` and name based on request method, such as `HTTP GET`,
such as `ApplicationFilterChain.doFilter` or `FrameworkServlet.doGet`. or servlet/filter mapping corresponding to the requested path, such as `/foo/bar/*`.
Span created by Spring MVC instrumentation will have `kind=INTERNAL` and named `OwnerController.initCreationForm`. Span created by Spring MVC instrumentation will have `kind=INTERNAL` and named `OwnerController.initCreationForm`.
The state described above has one significant problem. The state described above has one significant problem.
Observability backends usually aggregate traces based on their root spans. Observability backends usually aggregate traces based on their root spans.
This means that ALL traces from any application deployed to Servlet container will be grouped together. This means that for applications with a single controller Servlet that services all requests ALL
Because their root spans will all have the same named based on common entry point. traces from that application will be grouped together because their root spans will all have the same
named based on common entry point.
In order to alleviate this problem, instrumentations for specific frameworks, such as Spring MVC here, In order to alleviate this problem, instrumentations for specific frameworks, such as Spring MVC here,
_update_ name of the span corresponding to the entry point. _update_ name of the span corresponding to the entry point.
Each framework instrumentation can decide what is the best span name based on framework implementation details. Each framework instrumentation can decide what is the best span name based on framework implementation details.