Azure Functions timeout

Everything about function app timeout

 

Issue:

·       Timeout value of 00:05:00 exceeded by function?

·       What is azure functions timeout?

·       What is azure functions execution timeout?

·       What is default timeout in azure function?

·       Consumption plan timeout?

·       Premium plan timeout?

 

Solution:

What is timeout?  In business logic language, a timeout is a specified period of time that will be allowed to complete an operation and if that operation doesn’t complete within specified period of time then it will throw some exception. Timeouts allow for more efficient usage of limited resources without requiring additional interaction from the agent interested in the goods that cause the consumption of these resources.

A common example is your smart phone turn off backlight after a certain time when idle which you can set.

Similarly, Azure has set the timeout for function app and it is very important to understand it as you can develop/write your business logic and optimize it accordingly.

In Azure functions, timeout means if your business logic or code should be optimized enough to complete with timeout duration otherwise it throws exception like “Timeout value of 00:05:00 exceeded by function”

In Azure functions, timeout varies according to hosting plan and runtime versions.

Azure functions have 3 hosting plans,

• Consumption plan (Dynamic plan)
• Premium plan (Elastic premium plan)
• App Service plan (Dedicated plan

And as of now it has 3 runtime versions,

·       1.x

·       2.x

·       3.x

Where 1,2 and 3 is the major version and x stand for minor version e.g. 2.09234.

Now we know what azure functions execution timeout is? hence we should focus on

·       Default timeout,

·       maximum timeout

for each hosting plan.

You can check this information in the below list.

That means if you see exception like “Timeout value of 00:05:00 exceeded by function” then you quickly need to check if your function is hitting the default timeout.

Here you have 2 options,

1.      Investigate why your code execution is taking that much of time and optimize your code

2.      Increase the default timeout.

For first case you better know how to optimize the code.

How to modify the default timeout

Azure functions timeout value is stored and handled in host.json file and attribute name is functionTimeout

{     "functionTimeout": "00:05:00" }

 

functionTimeout indicated the timeout duration for all the functions and not for the single function.

You can update the default timeout value, save it, and test your function again.

In dedicated app service plan there is no limit but you should keep a fixed upper bound limit as unlimited timeout can have some disadvantages like your execution will keep executing and you will have to pay for it.

For unlimited timeout you can use -1

{

    "functionTimeout": "-1"

}

Important note

Regardless of the function app timeout setting, 230 seconds is the maximum amount of time that an HTTP triggered function can take to respond to a request. This is because of the default idle timeout of Azure Load Balancer. For longer processing times, consider using the Durable Functions async pattern or defer the actual work and return an immediate response.

Function timeout at function level

We know now that we can set function timeout in host.json but it is for all the function inside it. What about setting timeout for one or 2 function only.

While developing the functions from Visual Studio, you can now set the timeout at the function level.

Adding the attribute [Timeout("00:00:10")], above the function definition would set the timeout value for the function.  more details.

I did test the function executions to confirm that it doesn’t affect executions of other functions in the same function app.

With the test deployment I made – I deployed multiple function to the Function App on Azure, with only one of them (say function A) having the timeout set. While executing the functions, we see that A stops after the threshold timeout value and the others continue as expected.

Imp Note: This is for C# language only.

Output:

Hope this helps. Please let me know if you have any query

References:

https://docs.microsoft.com/en-us/azure/azure-functions/functions-scale

https://docs.microsoft.com/en-us/azure/azure-functions/functions-host-json#functiontimeout