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Lab 8 - Advanced feature - Timeouts

Before starting this lab, create a new folder for your files:

$ mkdir -p lab8 \
   && cd lab8

Extend timeouts with read_timeout

The timeout corresponds to how long a function can run for until it is executed. It is important for preventing misuse in distributed systems.

There are several places where a timeout can be configured for your function, in each place this is done through the use of environmental variables.

  • Function timeout

  • read_timeout - time allowed fo the function to read a request over HTTP

  • write_timeout - time allowed for the function to write a response over HTTP

  • exec_timeout - the maximum duration a function can run before being terminated

The API Gateway has a default of 20 seconds, so let's test out setting a shorter timeout on a function.

$ faas-cli new --lang python3 sleep-for --prefix="<your-docker-username-here>"

Edit handler.py:

import time
import os

def handle(req):
    """handle a request to the function
    Args:
        req (str): request body
    """

    sleep_duration = int(os.getenv("sleep_duration", "10"))
    preSleep = "Starting to sleep for %d" % sleep_duration
    time.sleep(sleep_duration)  # Sleep for a number of seconds
    postSleep = "Finished the sleep"
    return preSleep + "\n" + postSleep

Now edit the sleep-for.yml file and add these environmental variables:

provider:
  name: openfaas
  gateway: http://127.0.0.1:8080

functions:
  sleep-for:
    lang: python3
    handler: ./sleep-for
    image: <your-docker-username-here>/sleep-for:0.1
    environment:
      sleep_duration: 10
      read_timeout: "5s"
      write_timeout: "5s"
      exec_timeout: "5s"

Use the CLI to build, push, deploy and invoke the function.

$ echo | faas-cli invoke sleep-for
Server returned unexpected status code: 502 -

You should see it terminate without printing the message, because the sleep_duration is higher than the timeout values.

Now set sleep_duration to a lower number like 2 and run faas-cli deploy again. You don't need to rebuild the function when editing the function's YAML file.

$ echo | faas-cli invoke sleep-for
Starting to sleep for 2
Finished the sleep
  • API Gateway

To set expanded timeouts for your functions beyond the default limit, follow the following tutorial: Expanded timeouts

Now move onto Lab 9