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c#azureazure-functionsazure-durable-functions
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Reputation: 16238

Azure Durable Function - counter in orchestration

I'm building a Durable Function based on the monitor pattern. I have the code below and my question is regarding the counter variable which I used for a simple exponential retry-backoff.

[FunctionName("RequestOrchestrator")]
public static async Task RequestOrchestrator(
    [OrchestrationTrigger] DurableOrchestrationContext monitorContext, ILogger log)
{
    DateTime endTime = monitorContext.CurrentUtcDateTime.AddHours(1);
    int counter = 0;

    while (monitorContext.CurrentUtcDateTime < endTime)
    {
        var result = await monitorContext.CallActivityAsync<bool>("GetStatusExternal", "test");

        if (result)
        {
            // all ok
            break;
        }
        else
        {
            counter++;
            // Wait for the next checkpoint with exponential backoff
            var nextCheckpoint = monitorContext.CurrentUtcDateTime.AddSeconds(5 * counter);
            if (!monitorContext.IsReplaying)
            {
                log.LogInformation($"Next check at {nextCheckpoint}.");
            }

            await monitorContext.CreateTimer(nextCheckpoint, CancellationToken.None);
        }
    }
}

Is the usage of the counter ok like this or does the counter++ need to go into 

if (!monitorContext.IsReplaying)
  counter++;

for it to be replay-safe?

Upvotes: 0

Views: 808

Answers (1)

PramodValavala
PramodValavala

Reputation: 6657

No. You don't need the monitorContext.IsReplaying check around counter++.
You need this check only for statements you want to be run just once like logging (as in your code), status updates to an external system, etc.

To be replay-safe, you basically just need your code to be deterministic. So any code that can't be constituted in a Pure Function has to be moved into their own activity functions. Everything else will do.

Like the documentation states, any code that changes over time (replay times) like time-based generators, remote data from external APIs, etc. has to be in activity functions.

Upvotes: 3

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