Describes the cause and action for error messages.
Error Message(English)：
error cloning com_github_grpc_grpc
Can't build by Bazel as an external imported project. ・ Issue ... - GitHub
https://github.com/grpc/grpc/issues/12122
proxy環境下でgit cloneするまで（503エラーを超えて） - Qiita
https://qiita.com/fam_taro/items/c3db8b4fcef14e66eab7
Cloning git repo results in error - Stack Overflow
https://stackoverflow.com/questions/39851569/cloning-git-repo-results-in-error
grpc / Building gRPC services with bazel and rules_protobuf
https://grpc.io/blog/bazel_rules_protobuf