Python Plugin System over gRPC

This project is a port/wrapper over github.com/hashicorp/go-plugin, that implements the client (host) in Python, as opposed to Go.

The `hashicorp/go-plugin` project

go-plugin is a Go (golang) plugin system over RPC. It is the plugin system that has been in use by HashiCorp tooling for over 4 years. While initially created for Packer, it is additionally in use by Terraform, Nomad, and Vault.

While the plugin system is over RPC, it is currently only designed to work over a local [reliable] network. Plugins over a real network are not supported and will lead to unexpected behavior.

This plugin system has been used on millions of machines across many different projects and has proven to be battle hardened and ready for production use.

`pygo-plugin` Features

Like hashicorp/go-plugin, this system supports a number of features:

Plugins are gRPC interface implementations.
For a plugin author: you just implement an interface as if it were going to run in
the same process.
For a plugin user: you just use and call functions on an interface as if it were in the same process.
This plugin system handles the communication in between.

Cross-language support. Plugins can be written (and consumed) by almost every major language. This library supports serving plugins via gRPC. gRPC-based plugins enable plugins to be written in any language.

Built-in Logging. Any plugins that use the log standard library will have log data automatically sent to the host process. The host process will mirror this output prefixed with the path to the plugin binary. This makes debugging with plugins simple.

Protocol Versioning. A very basic "protocol version" is supported that can be incremented to invalidate any previous plugins. This is useful when interface signatures are changing, protocol level changes are necessary, etc. When a protocol version is incompatible, a human friendly error message is shown to the end user.

TTY Preservation. Plugin subprocesses are connected to the identical stdin file descriptor as the host process, allowing software that requires a TTY to work. For example, a plugin can execute ssh and even though there are multiple subprocesses and RPC happening, it will look and act perfectly to the end user.

Host upgrade while a plugin is running. Plugins can be "reattached" so that the host process can be upgraded while the plugin is still running. This requires the host/plugin to know this is possible and daemonize properly. Client takes a ReattachConfig to determine if and how to reattach.

Roadmap

This project is in early stages as is currently considered "alpha".

Tests
Documentation
Additional examples

Feature parity with hashicorp/go-plugin:

Architecture

See hashicorp/go-plugin for general plugin system architecture.

The host (client) python implementation uses a binding over hashicorp/go-plugin to load and manage the lifecycle of plugins as subprocesses. Bindings are generated using go-python/gopy.

The server (plugin) python implementation is a pure port of the equivalent Go library. This helps to extend support to Python plugins for more easily serving the plugin, syncing stdout/stderr and logging output, graceful shutdowns, protocol and version checking, TLS, and so on. As per go-plugin documentation, plugins can be written in any language without a specific server implementation, but do not automatically gain these extended features.

Requirements

Building the pygo-plugin library requires a recent version of the Go compiler (>= 1.15).

The python development headers are required to compile the python extension module. On linux:

sudo apt install libpython3-dev build-essential

The gopy and goimports tools must also be installed, to support generating the bindings from Go to Python:

go get golang.org/x/tools/cmd/goimports
go get github.com/go-python/gopy@master

After these tools are available, the build script will be able to generate bindings, and run the protobuf code generation.

# Install python dependencies.
pip install -r requirements.txt

# Install pygo
python setup.py install

# or... to hack on the source
python setup.py develop

Usage

To use the plugin system, you must take the following steps. These are high-level steps that must be done. Examples are available in the pygo_plugin/_examples directory.

Write the gRPC Protocol Buffers interface that you want to expose for plugins.
For each interface, implement an implementation of that gRPC proto that communicates over a gRPC connection. You'll have to implement both a client and server implementation.
Create a Plugin class implementation that knows how to create the RPC client/server for a given plugin type.
Plugin authors call pygo_plugin.serve to serve a plugin from the main function.
Plugin users use pygo_plugin.Client to launch a subprocess and request an interface implementation over RPC.

moddyz/pygo-plugin