FPS

FPS (Fast Pluggable Server), is a framework designed to compose and run a web-server based on plugins. It is based on top of FastAPI, uvicorn, typer, and pluggy.

Motivation

To better understand the motivations behind this project, please refer to the Jupyter server team compass.

How it works

The main purpose of FPS is to provide hooks to register endpoints, static mounts, CLI setups/teardowns, etc.

An application can then be composed by multiple plugins providing specific/specialized endpoints. Those can be registered using fps.hooks.register_router with a fastapi.APIRouter.

What is coming soon

The most important parts will be to have a nice configuration system and also a logger working through multiprocesses, with homogeneous formatters to give devs/ops/users a smooth experience.

Concepts

Few concepts are extensively used in FPS:

• a hook, or hook implementation, is a method tagged as implementing a hook specification
  • a hook specification is the declaration of the hook

    @pluggy.HookspecMarker(HookType.ROUTER.value)
    def router() -> APIRouter:
        pass
    

  • hooks are automatically collected by FPS using Python's entry_points, and ran at the right time

    [options.entry_points]
    fps_router =
        fps_helloworld_router = fps_helloworld.routes
    fps_config =
        fps_helloworld_config = fps_helloworld.config
    

  • multiple entry_points groups are defined (e.g. fps_router, fps_config, etc.)
    • a hook MUST be declared in its corresponding group to be collected
    • in the previous example, HookType.ROUTER.value equals fps_router, so the router hook is declared in that group
  • fps.hooks.register_<hook-name> helpers are returning such hooks

    def register_router(r: APIRouter):
        def router_callback() -> APIRouter:
            return r
    
        return pluggy.HookimplMarker(HookType.ROUTER.value)(
            function=router_callback, specname="router"
        )
    

• a plugin is a Python module declared in a FPS's entry_point
  • a plugin may contain zero or more hooks
  • in the following helloworld example, the hook config is declared but not the plugin_name one. Both are hooks of the fps_config group.

    from fps.config import PluginModel
    from fps.hooks import register_config
    
    
    class HelloConfig(PluginModel):
        random: bool = True
    
    
    c = register_config(HelloConfig)
    

• a plugins package is a Python package declaring one or more plugins

Configuration

FPS now support configuration using toml format.

Precedence order

For now, the loading sequence of the configuration is: fps.toml < <plugin-name>.toml < <cli-passed-file> < <cli-arg>.

fps.toml and <cli-passed-file> files can contain configuration of any plugin, while <plugin-name>.toml file will only be used for that specific plugin.

fps.toml and <plugin-name>.toml currently have to be in the current working directory. Support for loading from user home directory or system-wide application directory will be soon implemented.

Note: the environment variable FPS_CONFIG_FILE is used to store cli-passed filename and make it available to subprocesses.

Merging strategy

At this time the merging strategy between multiple config sources is pretty simple:

• dict values for higher precedence source win
• no appending/prepending on sequences

Testing

FPS has a testing module leveraging pytest fixtures and fastAPI dependencies override.