Azure Function App 503 Error

Question

Azure Function App 503 Error

Pramodhi 0

Suddenly it starts throwing 503 error and lasts for 4,5 minutes get resolved automatically. User's image

Andriy Bilous 11,821 Reputation points MVP Volunteer Moderator

2025-05-30T04:38:34.88+00:00
Here are Suggested Immediate Steps

Check Azure Portal > Function App > App Insights > Failures – to see if requests are hitting the function.

If you can share:

Hosting plan (Consumption, Premium, Dedicated)

Type of trigger (HTTP, Timer, etc.)

Logs from App Insights

App code architecture (e.g., does the PUT route call a backend service?)

I can give you even more targeted advice.

What could be the reason

Cold Starts + Scale-out Delay (Common in Consumption Plan)

When traffic suddenly spikes or after a period of idleness, Azure needs to allocate containers to serve requests.

The cold start delay + container provisioning can result in temporary 503s.

Typically resolved once enough instances spin up — hence your “4–5 minutes” window.

App Service Infrastructure Maintenance

Azure might be restarting or updating the underlying VM or container host (even without alerting you).

This will drop connections temporarily, causing a short burst of 503s.
Shireesha Eeraboina 3,435 Reputation points Microsoft External Staff Moderator

2025-06-03T00:58:28.4566667+00:00

Hi Pramodhi,

I hope you had a chance to review the response above. If you are still facing the issue, could you please check the private message and provide the required details for further troubleshooting?
Praveen Kumar Gudipudi 1,875 Reputation points Microsoft External Staff Moderator

2025-06-05T00:58:46.27+00:00

Hello Pramodhi,

Following up to see if you have chance to check my previous response and please let us know with an update to assist you further on this.
Praveen Kumar Gudipudi 1,875 Reputation points Microsoft External Staff Moderator

2025-06-09T00:36:38.6+00:00

Hello Pramodhi,

We haven't heard back from you yet, and I wanted to ensure everything is on track and see if there's anything more, we can assist you with.

1 answer

Your answer

Andriy Bilous 11,821 Reputation points MVP Volunteer Moderator

2025-05-30T04:38:34.88+00:00

Here are Suggested Immediate Steps

Check Azure Portal > Function App > App Insights > Failures – to see if requests are hitting the function.

If you can share:

Hosting plan (Consumption, Premium, Dedicated)

Type of trigger (HTTP, Timer, etc.)

Logs from App Insights

App code architecture (e.g., does the PUT route call a backend service?)

I can give you even more targeted advice.

What could be the reason

Cold Starts + Scale-out Delay (Common in Consumption Plan)

When traffic suddenly spikes or after a period of idleness, Azure needs to allocate containers to serve requests.

The cold start delay + container provisioning can result in temporary 503s.

Typically resolved once enough instances spin up — hence your “4–5 minutes” window.

App Service Infrastructure Maintenance

Azure might be restarting or updating the underlying VM or container host (even without alerting you).

This will drop connections temporarily, causing a short burst of 503s.
Shireesha Eeraboina 3,435 Reputation points Microsoft External Staff Moderator

2025-06-03T00:58:28.4566667+00:00

Hi Pramodhi,

I hope you had a chance to review the response above. If you are still facing the issue, could you please check the private message and provide the required details for further troubleshooting?
Praveen Kumar Gudipudi 1,875 Reputation points Microsoft External Staff Moderator

2025-06-05T00:58:46.27+00:00

Hello Pramodhi,

Following up to see if you have chance to check my previous response and please let us know with an update to assist you further on this.
Praveen Kumar Gudipudi 1,875 Reputation points Microsoft External Staff Moderator

2025-06-09T00:36:38.6+00:00

Hello Pramodhi,

We haven't heard back from you yet, and I wanted to ensure everything is on track and see if there's anything more, we can assist you with.

Answer 1

Hello Pramodhi

What could be the reason

Cold Starts + Scale-out Delay (Common in Consumption Plan)

When traffic suddenly spikes or after a period of idleness, Azure needs to allocate containers to serve requests.
The cold start delay + container provisioning can result in temporary 503s.
Typically resolved once enough instances spin up — hence your “4–5 minutes” window.

App Service Infrastructure Maintenance

Azure might be restarting or updating the underlying VM or container host (even without alerting you).
This will drop connections temporarily, causing a short burst of 503s.What could be the reason
1. Cold Starts + Scale-out Delay (Common in Consumption Plan)
- When traffic suddenly spikes or after a period of idleness, Azure needs to allocate containers to serve requests.
- The cold start delay + container provisioning can result in temporary 503s.
- Typically resolved once enough instances spin up — hence your “4–5 minutes” window.
1. App Service Infrastructure Maintenance
- Azure might be restarting or updating the underlying VM or container host (even without alerting you).
- This will drop connections temporarily, causing a short burst of 503s.

https://learn.microsoft.com/en-us/answers/questions/617732/azure-app-service-get-503-the-service-is-unavailab

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Azure Function App 503 Error

1 answer

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