Incorporate or integrate an external building system into envoy bazel build system

[Gary Tang]

Hello,

We're building an application binary that is composed of both envoy and fstack code.

envoy will talk/call to fstack rather than to Linux kernel. 

fstack is an open source code. fstack uses Makefile while envoy uses bazel. We don't plan to convert fstack makefiles into bazel.

We want to keep the build systems for both, that is, make envoy use bazel and fstack use makefile.

The problem is how to integrate the two build systems together?

We want to have envoy bazel call makefile to build fstack code and then use the built fstack library.

I did some research on the following and still not very clear how to do it. 

   https://stackoverflow.com/questions/57764066/bazel-rules-foreign-cc-using-cmake-binary-built-from-source-at-build-time

   https://github.com/bazelbuild/rules_foreign_cc

   https://blog.envoyproxy.io/external-c-dependency-management-in-bazel-dd37477422f5

Can anyone shed light on this? 

Thanks

Gary