Hosting the bot on AWS Lambda

Why AWS Lambda

With Heroku removing free tiers it's natural to seek free alternatives. AWS has a free tier with generous limits. Serverless setup with Lambdas is free for a year and cheap afterward. Resources are only allocated when your bot is triggered, so we need to setup a webhook. There are plenty of articles on how to do that, basically, run

curl -GET https://api.telegram.org/bot{BOT_TOKEN}}/setWebhook?url={GATEWAY_URL | FUNCTION_URL}

Limitations

However, AWS Lamda currently doesn't support async invocations for Python, and with PTB v20.x we should work around that. To make it work, feel free to use the following example:

import asyncio
from telegram.ext import Application

application = Application.builder().token(TELEGRAM_API_KEY).build()


def lambda_handler(event, context):
    return asyncio.get_event_loop().run_until_complete(main(event, context))

async def main(event, context):
    # Add conversation, command, and any other handlers
    
    try:    
        await application.initialize()
        await application.process_update(
            Update.de_json(json.loads(event["body"]), application.bot)
        )
    
        return {
            'statusCode': 200,
            'body': 'Success'
        }

    except Exception as exc:
        return {
            'statusCode': 500,
            'body': 'Failure'
        }

Lambda setting for Code / Runtime Settings / Handler should point to {main_file}.lambda_handler, e.g. bot.lambda_handler

This asyncio pattern is far from ideal as described here, but it works as expected.