How-to install Prometheus Client in the C++ SDK CI Environment

[CunjunWang]

Is your feature request related to a problem?
Yes it is. The C++ Prometheus Exporter uses the Prometheus client as a project dependency, so we need to install it in the CI environment to build the project. Currently we have found three ways to address this issue:

1. Install the Prometheus Client in a Windows/Visual Studio IDE environment with vcpkg, and write similar scripts to install and setup in Linux and MacOS.
2. Use git submodule and include Prometheus client as a submodule of the OpenTelemetry-cpp project.
3. Use a Github Actions to add a linux container and install the dependencies for testing.

We would like to get definitive guidance on the best way to install the Prometheus client specific to the OpenTelemetry C++ environment. Currently this is a blocker for us to complete our Prometheus exporter (#280) project.

Describe the solution you'd like
We have provided the pros and cons of all three solutions.

1: Using vcpkg for Windows and writing additional scripts for Linux and MacOS:

• Pros:
  • Conforms to the current process in the project to add new dependencies.
• Cons:
  • Maintaining multiple scripts customized for each OS is not ideal from a maintainability pov. As the project adds more functionality, it may add more dependencies too. Having multiple scripts for each OS will increase maintenance (CI and testing).
  • Lack of familiarity with C++ repo CI configurations needs maintainer guidance on instructions on CI scripts.

2: Using git submodule

• Pros:
  • This is an organized and elegant way to manager third-party dependencies for C++ projects.
  • OpenTelemetry Java also uses this solution.
• Cons:
  • The environment for using git submodule is not setup yet in the project and may require some major changes in the project structure.
  • The CI setup may need to change accordingly. This is something we as members don’t have rights to do.

3: Using GitHub Actions

• Pros:
  • There are some examples in the OpenTelemetry-dotnet repo.
• Cons:
  • This needs familiarity on Docker and container setup.
  • Need more documentation to understand the workflow.
    • Is this container still a part of the CI test?
    • If the Prometheus client is installed in the container, how other CI tests pass when they are also dependent it to build?

[CunjunWang]

CI problems fixed.