Configurable Timer Triggers - Azure Web Jobs

Question

I'm building a job to trigger at some regular interval (say 1 minute). I've successfully used triggered web jobs with time-span hard coded in the functions.

public void foo([TimerTrigger("00:01:00")] TimerInfo timer)

Now if I ever want to change the trigger time from 1-min to 2-min I've to redeploy the code. Instead is there a way to make the TimeTrigger Configurable, from a config file.

Note that replacing the string with a dynamically read value isn't possible as the TimerTrigger Attribute is a const string expression or a Type.

Answer 1

After much digging, I've realized that this can be done with an SDK extension class TimerSchedule.

For it, you would need a base class that you'll be able to use for multiple triggers.

class CustomTimerTriggerBase: TimerSchedule
{
    TimeSpan timer;
    public CustomTimerTriggerBase(string triggerConfigKey)
    {
        timer=TimeSpan.Parse(ConfigurationManager.AppSettings[triggerConfigKey]);
    }

    public override DateTime GetNextOccurrence(DateTime now)
    {
        return now.Add(timer);
    }
}

Use this Base to generate your timers...

public sealed class FooTimer : CustomTimerTriggerBase
{
    public FooTimer() : base("FooTimerKey") {}
}

In your, App.config have a key for "FooTimer"

<add key="FooTimerKey" value="00:02:00" />

Use this FooTimer class in your webjob functions.

public void foo([TimerTrigger(typeof(FooTimer)] TimerInfo timer)

Now you can simply change the value in app config instead of redeploying the code. NOTE: Since you are using Timespan to parse, the string can be of any format you need as defined in TimeSpan formats.

---

UPDATE

As pointed by l--''''''---------'''''''''''' and Andy Dobedoe now (as of 2019) it is much simpler to achieve this.

public static async Task RunAsync([TimerTrigger("%MYCRON%")]TimerInfo myTimer

Finds the setting called MYCRON and uses the cron expression from there