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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: 5
      write_timeout: 5
      exec_timeout: 5

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

There is also a maximum timeout duration set at the gateway and it will override the function timeout. At the time of writing the maximum timeout is configured at "20s", but can be configured to a longer or shorter value.

Docker Swarm

To update the gateway value, set read_timeout and write_timeout in the docker-compose.yml file for the gateway and faas-swarm service then run ./deploy_stack.sh.

Kubernetes

To update the gateway value, set gateway.readTimeout and gateway.writeTimeout in the values.yaml file or use the Helm parameters --set gateway.readTimeout=value and --set gateway.writeTimeout=value.

Now move onto Lab 9