#449 Implement app_env.server, on_startup, on_shutdown decorators and pickled apps Pull request opened by cosmicBboy This PR introduces an

AppEnvironment.startup

decorator. This is a Python-native way to define app startup logic and supports pickling app environments so that users can do

flyte.with_servecontext(interactive_mode=True).serve(app_env)

. When a user defines

app_env.startup

, it will take the place of

args

, which typically creates a subprocess in the app container which runs that command. Instead, the

AppEnvironment

is loaded into the app container and the

AppEnvironment._startup_fn

is run. import fastapi import uvicorn import flyte import flyte.app env = flyte.app.AppEnvironment( name="pickled-app", image=flyte.Image.from_debian_base().with_pip_packages("fastapi", "uvicorn"), resources=flyte.Resources(cpu=1, memory="512Mi"), requires_auth=False, port=8080, ) @env.startup def fastapi_app(): # NOTE: since FastAPI cannot be pickled (because starlette.datastructures.State cannot be pickled due to # circular references), we need to use a factory pattern to create the app instance. In the startup function. app = fastapi.FastAPI() @app.get("/") async def root() -> str: return "Hello, World!" uvicorn.run(app, port=8080) if name == "__main__": import logging flyte.init_from_config(log_level=logging.DEBUG) app = flyte.with_servecontext(interactive_mode=True).serve(env) print(app.url) This PR also adds: • Support for module- and pickle-based app startup using the private

AppEnvironment._startup_fn

decorator. • Adds a

AppEnvResolver

class to rehydrate app environments in the

fserve

executable. • Adds support for pickling the

FastAPIAppEnvironment

with no user-facing SDK changes. flyteorg/flyte-sdk