Remove missing target in legacy prometheus

[owent]

Signed-off-by: owentou owentou@tencent.com

Fixes #1096

Changes

Remove missing target and fix document for exported config file.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #1097 (58edf22) into main (1867688) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1097   +/-   ##
=======================================
  Coverage   94.41%   94.41%           
=======================================
  Files         158      158           
  Lines        6077     6077           
=======================================
  Hits         5737     5737           
  Misses        340      340           

[lalitb]

Thanks for fixing this, looks like it got introduced while deprecating the old matrix implementation. Not related to this PR, but I feel it would be good to add the cmake install test too in the CI pipeline to catch these errors.

[owent]

Thanks for fixing this, looks like it got introduced while deprecating the old matrix implementation. Not related to this PR, but I feel it would be good to add the cmake install test too in the CI pipeline to catch these errors.

Need use prebuilt prometheus-cpp to catch this problem. It maybe will take a long time to build all dependencies.
In https://github.com/atframework/cmake-toolset/actions/runs/1499413005, it takes about 50 minutes to finish the job, most package in it is the dependencies of opentelemetry-cpp. So I wonder if we should do the same thing here, or should we cache the prebuilt files when the versions of dependencies not changed?

[lalitb]

Need use prebuilt prometheus-cpp to catch this problem.

I am not completely sure if that would have helped here. As I understand, the missing target error would have got caught during the otel-cpp installation, which we don't do in our CI pipeline.
But to speed up the CI pipeline, I feel it would be good to use some form of caching ( either using pre-built binaries of external dependencies as you mentioned or using cmake cache).
While I would merge this PR, we can continue discussing in this thread for any optimization we can do to speed-up pipeline.