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POC gRPC API for juju

The idea of this is to showcase gRPC by creating a proxy gRPC server for the juju client. Documentation and client APIs for Go and Python are generated from the protobuf specification.

Requirements

Tested on Linux / MacOS with python3 / pip3.

The protobuf spec

A service spec is defined in application.proto. The contents of gen/proto is generated from this. It contains

  • a go/ directory with
    • Generated code for Go client / server (generated with protoc-gen-go and protoc-gen-go-grpc);
    • Generated code for an HTTP gateway to a gRPC server (generated with protoc-gen-grpc-gateway);
  • a python/ directory with generated code for Python client (generated with grpcio-tools);
  • a doc/ directory with generated HTML documentation (with protoc-gen-doc).
  • an openapi/ directory with generated swagger specs

Generating the python / Go code and HTML docs

The buf is used to generate output from the protobuf specs as it streamlines the process a bit.

Some protoc dependencies need to be installed before generation can be run.

make install-deps

Then to re-generate the code / docs:

make generate

The gRPC server

This is implemented in cmd/grpc-juju. Run it and it starts

  • a gRPC server on port 8080 and
  • a gRPC gateway (HTTP server) on port 8090.

It can be installed directly without downloading the repo:

go install github.com/arnodel/grpc-juju-client/cmd/grpc-juju

It requires a juju client to be installed somewhere on the same machine. By default it assumes juju is in the path. You can pass in a custom path:

grpc-juju -juju-client ~/bin/juju

See apis/ for supported apis. Also the gRPC server supports reflection, so it is discoverable (use e.g. https://github.com/fullstorydev/grpcui to play with it)

Example clients

The clients/ directory contains two sample programming acting as clients to the gRPC server. In order to use them grpc-juju should be running on the same machine.

  • clients/go-client contains a Go client that can deploy or remove a deployment of postgresql and print the outcome.
  • clients/python-client contains a Python client with the same functionality. It should be run via the client.sh script to get the import paths correct.