Getting 503 Error message in Azure APIM API connected to Logic App Standard

Devender S 0

Getting 503 Error message in Azure APIM API connected to Logic App Standard.

APIM is in Premium tier and Logic App is having Standard plan with Elastic App Service Plan (WS2, Instance Count 4).

Checked Metrics in App Service and CPU usage is coming out to be more than 98% but Logic App Health Check shows everything under control and maximum usage less than 70%.

App Service is dedicated only to one Logic App.
What can be the issue?

Devender S 0 Reputation points

2024-12-11T09:43:07.9366667+00:00

Hello @Shireesha Eeraboina (Quadrant Resource LLC) ,

I am adding Logic App connection in APIM Backend and calling it from APIM Policy. There is no issue with the connection as it is working fine for 99% of the requests.

In case of 503, I don't see any run in the logic app workflow probably because it was not triggered due to service unavailability.

I have checked High CPU Analysis in Logic App, but it shows no concerns and usage is less than 70% of the CPU. However, App Service Plan connected to it shows 100% usage in a lot of cases. ASP is dedicated to same logic app and is not shared.
Devender S 0 Reputation points

2024-12-11T09:48:41.7466667+00:00

Hi @Shireesha Eeraboina (Quadrant Resource LLC) ,

We are configuring Logic App connection in APIM Backend and calling it from APIM Policy. There is no issue with the connection as it is working fine for 99% of the API calls.

We don't see any run history in logic app workflows probably because of server unavailability.

I have diagnosed Logic App but the usage shows no concerns and CPU usage is under 70% whereas App Service Plan (Elastic, WS2) is showing usage as 100% in a lot of cases. ASP is dedicated to this logic app and is not shared.
Shireesha Eeraboina (Quadrant Resource LLC) 575 Reputation points Microsoft Vendor

2024-12-12T06:52:12.12+00:00
Hi @Devender S,

Since the CPU usage is reaching 100%, it's a clear indicator that the Elastic App Service Plan (WS2) may not have sufficient resources to handle all incoming requests.

Solution:

Scale up the Elastic App Service Plan to a higher SKU (e.g., WS3) to provide more CPU and memory resources for the Logic App also to distribute the load across multiple instances if you are seeing high traffic

Could you please enable the APIM trace to identify the backend error occurring when a 503 status is returned in the request?

please refer the document below to get the APIM traces:

https://learn.microsoft.com/en-us/azure/api-management/api-management-howto-api-inspector#enable-tracing-for-an-api

Let me know if you have any further questions.

Thank you!
Devender S 0 Reputation points

2024-12-12T07:16:25.39+00:00

Hi @Shireesha Eeraboina (Quadrant Resource LLC) Thanks for the detailed points.

We tried to trace the endpoints but it worked fine for us each time.

Regarding the ASP plan, we are unable to understand why it is touching 100% capacity but Logic App Metrics and Insights show CPU and Memory under 70-80%. Since, it's a dedicated ASP for Logic App, both the metrics are not matching up.

Logic App health check is all green and no concerns are getting listed.

If you can guide around this, that will be great.
VenkateshDodda-MSFT 23,246 Reputation points Microsoft Employee

2024-12-12T07:23:29.39+00:00

@Devender S Thanks for your response, I have reached out to you over private message could you please help us with requested information to understand better.

1 answer

Shireesha Eeraboina (Quadrant Resource LLC) 575 Reputation points Microsoft Vendor

2024-12-10T09:01:09.2133333+00:00
Hi @Devender S,

Thanks for posting your question in Microsoft Q&A, apologize for any inconvenience caused on this.

Based on the shared information, I understand that you're facing an issue with the 503 while calling the logic app from APIM.

How this apim and logic are connected, are you calling APIM from logic app as action using the built-in connector? or are you importing the logic app as one API in APIM?

If you are importing an API, have you followed the documentation steps mentioned: (https://learn.microsoft.com/en-us/azure/api-management/import-logic-app-as-api).

When you call the logic app Api from the run history of logic app do you see it is getting triggerd and executed successfully without any issues?

You can also follow this troubleshooting steps to troubleshoot 503 errors in APIM

If are seeing high CPU on logic apps I would suggest you troubleshoot using the High CPU Analysis detector under Availability and Performance in Diagnose and solve problems of your logic app as shown screenshot or you can scale the logic app to next app service plan to isolate the issue.
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Getting 503 Error message in Azure APIM API connected to Logic App Standard

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