How is inactivity time accounted in a wsgi application on aws lambda? - aws-lambda

Question

The main question is: how is time accounted in a wsgi application deployed on aws Lambda?
Suppose I deploy the following simple Flask app:
from flask import Flask
app = Flask(__name__)
#app.route("/")
def hello():
return "Hello World!", 200
using Zappa on AWS Lambda, with the following configuration:
{
"dev": {
"app_function": "simple_application.app",
"profile_name": "default",
"project_name": "simple_application",
"runtime": "python3.7",
"s3_bucket": "zappa-deployments-RANDOM",
"memory_size": 128,
"keep_warm": false,
"aws_region": "us-east-1"
}
}
Now if AWS has a request for my website, it will spin up a container with my code inside and let it deal with the request. Suppose the request is served in 200ms.
Obviously the Lambda with the wsgi server inside continues running (Zappa by default makes the lambda run for at least 30s).
So now to the various subquestions:
How much time am I charged for the execution?
200ms because of the request duration
30s because of the below limit for my lambda execution time
until the lambda is killed by AWS to reclaim space (which could occur even 30-45 minutes after)
If another request come along (and the first one is still being served) will the second request spin up another Lambda container or it will be queued until a threshold time has passed?
I expected to be charged just for the 200ms by reading AWS Lambda pricing page, but I would bet on it charging for 30s because, after all, I'm the one who imposed such limit.
In case I'm just charged for 200ms (and subsequent requests time) but the container keeps running uninterruptly for 30-45 minutes, I have a third subquestion:
Suppose now that I want to use a global variable as a simple local cache and synchronize it with a database (let's say DynamoDB) before the container is killed.
To do this I would like to raise the execution time limit of my lambdas to 15m, then at lambda creation set a Timer to fire a function that synchronizes the state and aborts the function after 14m30s.
How would accounted running time change in this settings (i.e. with a Timer that fires after a certain amount of time)?
The proposed lambda code for this subquestion is:
from flask import Flask
from threading import Timer
from db import Visits
import sys
lambda_uuid = "SOME-UUID-OF-LAMBDA-INSTANCE"
# Collects number of visits
visits = 0
def report_visits():
Visits(uuid=lambda_uuid, visits=visits).save()
sys.exit(0)
t = Timer(14 * 60 + 30, report_visits)
t.start()
# Start of flask routes
app = Flask(__name__)
#app.route("/")
def hello():
visits = visits + 1
return "Hello World!", 200
Thanks in advance for any information.

Answer 1

Zappa by default makes the lambda run for at least 30s
I can find no documentation to support this, and further all the Zappa documentation I can find states that a Zappa function will end as soon as a response is returned (just like any other AWS Lambda function) and as such you are only billed for those milliseconds that it took to generate the response.
I do see that the default maximum execution time for a Zappa Lambda function is 30 seconds. Perhaps that is where you are confused? That setting simply tells AWS Lambda to kill your running function instance if it runs for that long.
I expected to be charged just for the 200ms by reading AWS Lambda pricing page, but I would bet on it charging for 30s because, after all, I'm the one who imposed such limit.
You would be charged for exactly how long your function runs. So if it runs for 200ms, then you are charged for 200ms.
In case I'm just charged for 200ms (and subsequent requests time) but the container keeps running uninterruptly for 30-45 minutes, I have a third subquestion:
It doesn't keep running that long, it ends when it returns a response.
You are telling Lambda to kill your function instance if it runs for more than 30 seconds, so it's never going to run for more than 30 seconds with your current settings.
The current maximum run time for an AWS Lambda function is 15 minutes, so it couldn't possibly run for 30-45 minutes anyway.