Nebari Extension System

Introduction

This guide is to help developers extend and modify the behavior of Nebari. We leverage the plugin system pluggy to enable easy extensibility. Currently, Nebari supports:

overriding a given stages in a deployment
adding additional stages before, after and between existing stages
arbitrary subcommands

We maintain an examples repository which contains up to date usable examples.

Installing a plugin

Registering a plugin should be easy for the end user. Plugins are either installed into your existing environment e.g.

pip install my-nebari-plugin

Alternatively if you only want to temporarily add an extension.

nebari --import-plugin path/to/plugin.py <command> ...
nebari --import-plugin import.module.plugin.path <command> ...

Developing an extension

The most important step to developing a plugin is ensuring that the setuptools entrypoint is set.

...

[project.entry-points.nebari]
my-subcommand = "path.to.subcommand.module"

...

Adding this one line to your pyproject.toml will ensure that upon installation of the package the Nebari plugins are registered.

Subcommands

Nebari exposes a hook nebari_subcommand which exposes the typer CLI instance. This allows the developer to attach any arbitrary number of subcommands.

from nebari.hookspecs import hookimpl

import typer


@hookimpl
def nebari_subcommand(cli):
    @cli.command()
    def hello(
        name: str = typer.Option(
            "Nebari", help="Who to say hello to"
        )
    ):
        print(f"Hello {name}")

There is a dedicated working example in nebari-plugin-examples.

Stages

Nebari exposes a hook nebari_stage which uses the NebariStage class. NebriStage exposes render, deploy, destroy as arbitrary functions calls. See below for a complete example.

Nebari decides the order of stages based on two things the name: str attribute and priority: int attribute. The rules are as follows:

stages are ordered by priority
stages which have the same name the one with highest priority number is chosen

import contextlib
import os
from typing import Dict, Any

from nebari.hookspecs import hookimpl, NebariStage


class HelloWorldStage(NebariStage):
    name = "hello_world"
    priority = 100

    def render(self):
        return {
            "hello_world.txt": "File that says hello world"
        }

    @contextlib.contextmanager
    def deploy(self, stage_outputs: Dict[str, Dict[str, Any]]):
        print("I ran deploy")
        # set environment variables for stages that run after
        os.environ['HELLO'] = 'WORLD'
        # set output state for future stages to use
        stage_outputs[self.name] = {'hello': 'world'}
        yield
        # cleanup after deployment (rarely needed)
        os.environ.pop('HELLO')

    def check(self, stage_outputs: Dict[str, Dict[str, Any]]):
        if 'HELLO' not in os.environ:
            raise ValueError('stage did not deploy successfully since HELLO environment variable not set')

    @contextlib.contextmanager
    def destroy(self, stage_outputs: Dict[str, Dict[str, Any]], status: Dict[str, bool]):
        print('faking to destroy things for hello world stage')
        yield


@hookimpl
def nebari_stage():
    return [HelloWorldStage]

There is a dedicated working example in nebari-plugin-examples.