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Timer Trigger Functions

The time-triggered Azure Function allows us to schedule time for executing the function. It means that it triggers the function on a specified time. It works as CRON expressions work. When creating a time-triggered function, we need to specify a time in CRON format that determines when the trigger will execute. The CRON expression consists of six parts - second, minute, hour, day, month, and day of the week in Azure Function and each part is separated by space. Unlike HTTP-triggered Azure functions, timing info is stored in an Azure storage account so for any trigger functions you need to create an Azure storage account, for more information about creating Azure storage account see this Link

Tutorial

1. Create a new directory for the function app

mkdir TimerTrigger
cd TimerTrigger

2. Initialize the directory for functions

func init . --docker

Select dotnet

3. Add a new timer trigger function

func new

Select TimerTrigger then select a name for your function.

4. Run function

func start

Keda yaml file

for deploy keda on your kubernetes cluster the yaml file would be like this (see complete file):

apiVersion: keda.sh/v1alpha1
kind: ScaledObject
metadata:
  name: timer-trigger-function-with-keda
  namespace: keda-namespace
spec:
  scaleTargetRef:
    name: timer-trigger-function-with-keda
  minReplicaCount: 0
  maxReplicaCount: 20
  triggers:
    - type: cron
      metadata:
        timezone: Asia/Tehran #Required
        start: 0 0 * * * #Required
        end: 59 23 * * * #Required
        desiredReplicas: "10" #Required

there are some important things in KEDA to be explain

  • kind: ScaledObject tells kubernetes that this service is for keda and use for auto scalling
  • scaleTargetRef consider that KEDA should trigger which service that run on kubernetes for detecting auto scalling when service was busy and needs more pods (in this case we first create deployment named timer-trigger-function-with-keda)
  • triggers consider type of scaled object, there several trigger types, for Timer Trigger function use Cron
  • timezone One of the acceptable values from the IANA Time Zone Database. The list of timezones can be found here
  • start Cron expression indicating the start of the cron schedule.
  • end Cron expression indicating the end of the cron schedule.
  • desiredReplicas Number of replicas to which the resource has to be scaled between the start and end of the cron schedule.

Notice: Start and end should not be same.

For example, the following schedule is not valid:

start: 30 * * * *
end: 30 * * * *

Having all that configured we can now deploy the YAML file to AKS.

kubectl apply -f .\timer-trigger-deploy.yml

To check if everything is working, check the deployment.

> kubectl get deploy
NAME                        READY   UP-TO-DATE   AVAILABLE   AGE
 timer-trigger-function-with-keda            0/0     0            0           20h

> kubectl get ScaledObject
NAME                       SCALETARGETKIND           SCALETARGETNAME             TRIGGERS      AUTHENTICATION   READY   ACTIVE      AGE
timer-trigger-function-with-keda   apps/v1.Deployment   timer-trigger-function-with-keda            cron                       True      False     20h