App: Move AutoScaler dependency to extra requirements (#15971)

* Make autoscaler dependency optional
* update chglog
* dont directly import aiohttp

(cherry picked from commit 346e936)

# Conflicts:
#	requirements/app/base.txt
#	src/lightning_app/CHANGELOG.md

Author: akihironitta

requirements/app/base.txt

@@ -12,5 +12,3 @@ beautifulsoup4>=4.8.0, <4.11.2
 inquirer>=2.10.0
 psutil<5.9.4
 click<=8.1.3
-s3fs>=2022.5.0, <2022.8.3
-aiohttp>=3.8.0, <=3.8.3

requirements/app/cloud.txt

@@ -3,3 +3,5 @@
 redis>=4.0.1, <=4.2.4
 docker>=5.0.0, <=5.0.3
 # setuptools==59.5.0
+s3fs>=2022.5.0, <2022.8.3
+aiohttp>=3.8.0, <=3.8.3

requirements/app/components.txt

@@ -1,2 +1,3 @@
 # deps required by components in the lightning app repository (src/lightning_app/components)
 lightning_api_access>=0.0.3
+aiohttp>=3.8.0, <=3.8.3

src/lightning_app/CHANGELOG.md

@@ -13,7 +13,10 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Added the CLI command `lightning delete app` to delete a lightning app on the cloud ([#15783](https://github.com/Lightning-AI/lightning/pull/15783))
 - Added a CloudMultiProcessBackend which enables running a child App from within the Flow in the cloud ([#15800](https://github.com/Lightning-AI/lightning/pull/15800))
 - Utility for pickling work object safely even from a child process ([#15836](https://github.com/Lightning-AI/lightning/pull/15836))
-- Added `AutoScaler` component ([#15769](https://github.com/Lightning-AI/lightning/pull/15769))
+- Added `AutoScaler` component (
+   [#15769](https://github.com/Lightning-AI/lightning/pull/15769),
+   [#15971](https://github.com/Lightning-AI/lightning/pull/15971)
+)
 - Added the property `ready` of the LightningFlow to inform when the `Open App` should be visible ([#15921](https://github.com/Lightning-AI/lightning/pull/15921))
 - Added private work attributed `_start_method` to customize how to start the works ([#15923](https://github.com/Lightning-AI/lightning/pull/15923))
 - Added a `configure_layout` method to the `LightningWork` which can be used to control how the work is handled in the layout of a parent flow ([#15926](https://github.com/Lightning-AI/lightning/pull/15926))

src/lightning_app/components/auto_scaler.py

@@ -8,8 +8,6 @@
 from itertools import cycle
 from typing import Any, Dict, List, Tuple, Type
 
-import aiohttp
-import aiohttp.client_exceptions
 import requests
 import uvicorn
 from fastapi import Depends, FastAPI, HTTPException, Request
@@ -22,8 +20,13 @@
 from lightning_app.core.flow import LightningFlow
 from lightning_app.core.work import LightningWork
 from lightning_app.utilities.app_helpers import Logger
+from lightning_app.utilities.imports import _is_aiohttp_available, requires
 from lightning_app.utilities.packaging.cloud_compute import CloudCompute
 
+if _is_aiohttp_available():
+    import aiohttp
+    import aiohttp.client_exceptions
+
 logger = Logger(__name__)
 
 
@@ -114,6 +117,7 @@ class _LoadBalancer(LightningWork):
         \**kwargs: Arguments passed to :func:`LightningWork.init` like ``CloudCompute``, ``BuildConfig``, etc.
     """
 
+    @requires(["aiohttp"])
     def __init__(
         self,
         input_type: BaseModel,

src/lightning_app/utilities/imports.py

@@ -141,4 +141,8 @@ def _is_sqlmodel_available() -> bool:
     return module_available("sqlmodel")
 
 
+def _is_aiohttp_available() -> bool:
+    return module_available("aiohttp")
+
+
 _CLOUD_TEST_RUN = bool(os.getenv("CLOUD", False))