Azure Webjob: Type Triggered, works with singleton principle or not?

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Azure Webjob: Type Triggered, works with singleton principle or not?

Vikas Singh 20

Hi, I am looking into the Azure webjobs, trigger type: Triggered. I have a webjob that run's every 5 mins. In the public documentation it is mentioned that by default they are singleton or running with single instance. There is not much detail about what singleton means here. For example: the webjob get's triggered (n+1)th time, while the nth run of the webjob is still running. Does this mean the (n+1)th run will not be executed as long as the nth run finishes? Or does it mean that both the run will be executed but then both the runs are using a different instance. This is a bit confusing, could you pls help with the understanding.

Vikas Singh 20 Reputation points

2026-06-02T10:08:51.7633333+00:00

@Praneeth Maddali Tnks for the detailed breakdown. It's pretty clear.

The confusion mostly came from the following documentation: https://learn.microsoft.com/en-us/azure/app-service/overview-webjobs#scaling-considerations
Praneeth Maddali 10,025 Reputation points Microsoft External Staff Moderator

2026-06-03T00:27:37.01+00:00

Hi @Vikas Singh

I’m glad to hear your positive response and appreciate you sharing the update.

Just checking in to see if the earlier answer helped resolve your query. If it did, please click “Accept the answer” and consider upvoting it—this can be helpful for other community members who might face a similar issue.

If you have any further questions or need additional assistance, please feel free to let us know. We’re here to help!

Answer accepted by question author

Praneeth Maddali 10,025 Microsoft External Staff Moderator

Hi @Vikas Singh

Thanks for reaching out with your question about Triggered Azure WebJobs and how the singleton behavior works.

Quick Explanation

By default, Triggered WebJobs (including scheduled ones) have is_singleton set to false. This means:

The job always runs on one App Service instance (Azure selects it automatically).
If a new trigger fires while the previous run is still executing, a second instance of the job can start in parallel on the same App Service instance.

If you want to prevent overlapping runs (i.e., ensure the next execution waits until the current one finishes), you can enable singleton mode.

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Vikas Singh 20 Reputation points

2026-06-02T10:08:51.7633333+00:00

@Praneeth Maddali Tnks for the detailed breakdown. It's pretty clear.

The confusion mostly came from the following documentation: https://learn.microsoft.com/en-us/azure/app-service/overview-webjobs#scaling-considerations
Praneeth Maddali 10,025 Reputation points Microsoft External Staff Moderator

2026-06-03T00:27:37.01+00:00

Hi @Vikas Singh

I’m glad to hear your positive response and appreciate you sharing the update.

Just checking in to see if the earlier answer helped resolve your query. If it did, please click “Accept the answer” and consider upvoting it—this can be helpful for other community members who might face a similar issue.

If you have any further questions or need additional assistance, please feel free to let us know. We’re here to help!

Answer 1

For Azure WebJobs, “singleton” has two distinct aspects: how many instances of the job run across scaled-out App Service instances, and how many concurrent runs of the same job instance are allowed.

Default singleton behavior
- For continuous WebJobs, is_singleton defaults to true, which means only one instance of that WebJob runs across all scaled-out App Service instances.
- For triggered WebJobs, is_singleton defaults to false; they run on a single App Service instance by design, but multiple runs of the same job can overlap unless you explicitly enforce singleton behavior.
Controlling singleton behavior with settings.job The settings.job file lets you control concurrency and behavior:
```
   {
     "is_singleton": true,
     "run_mode": "scheduled"  // or "on_demand" / "continuous" as needed
   }
```
- is_singleton: true ensures only one instance of the job runs across all scaled-out instances.
- For a triggered job that runs every 5 minutes, if is_singleton is true and a new trigger fires while a previous run is still executing:
  - The (n+1)th run will not start until the nth run has finished. The job is effectively serialized.
- If is_singleton is false (the default for triggered jobs):
  - A new trigger can start another run in parallel with the existing one, on the same instance.
Summary for the described scenario
- Triggered WebJob, scheduled every 5 minutes:
  - With is_singleton: true: runs are non-overlapping; (n+1) waits for n to complete.
  - With is_singleton: false (default): runs can overlap; (n+1) may start even if n is still running, on the same instance.

To guarantee that only one run is ever active at a time for a triggered WebJob, configure is_singleton: true in settings.job.

References:

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Azure Webjob: Type Triggered, works with singleton principle or not?

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