App Service Linux restarted due to low swap space

Question

App Service Linux restarted due to low swap space

Personaify 10

Hi,

I'm running into a problem where my Linux app service is being restarted in the middle of running through its work queue. From the diagnostic tool, it says due to LowSwapSpace.

Here's the swap space chart, he uptick at the end is after it got restarted.

User's image

Here's the memory usage, looks fine:

User's image

Disk space usage is also fine:

User's image

The app service is running a docker container that contains my python app. This is the only app running on the App Service Plan and I'm on a B2 instance which should have 3.5gb of ram and 10gb of disk space. Which should be plenty.

How do I resolve this?

How do I increase the swap space available to the VM?

It doesn't seem like scaling up would resolve this issue?

Thanks!

ajkuma 28,036 Reputation points Microsoft Employee Moderator

2023-07-19T07:14:58.56+00:00

@Personaify , Just checking in to see if you had got a chance to see the previous responses . If the answer helped (pointed, you in the right direction) > please click Accept Answer Or please share the requested/more info to help you better.

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ajkuma 28,036 Reputation points Microsoft Employee Moderator

2023-07-19T07:14:58.56+00:00

@Personaify , Just checking in to see if you had got a chance to see the previous responses . If the answer helped (pointed, you in the right direction) > please click Accept Answer Or please share the requested/more info to help you better.

Answer 1

SUNOJ KUMAR YELURU 15,491 MVP Volunteer Moderator

Hello @Personaify

Thanks for posting in Q & A forum.Please verify that recycling events are occurring as a result of memory auto-healing in EventLog.xml.

With auto healing, the worker process that is hosting your web application can be recycled automatically. When that occurs, an event will also be recorded in the eventlog.xml file. (found in Logfiles folder of your web root directory).

Please turn on Always On from Azure Portal if it's not already.Select Configuration>Select General settings>For Always On, select On. Screenshot 2023-07-15 164121

Fetch more details about the issue in app service diagnostics

Porpoise 0 Reputation points

2023-07-16T19:55:25.8466667+00:00

Hi Sunoj, Always On is already enabled, but I don't see any EventLog.xml files in the LogFiles folder. I only see the normal docker logs.

But the issue is I don't want the web server restarted at all due to low swap space, because it loses its in progress work.
Porpoise 0 Reputation points

2023-07-16T19:58:44.0533333+00:00

Hi Sunoj, Always On is already enabled and I don't see an event.xml in the LogFiles directly. I only see the normal docker logs.

The issue is that I don't want any web server restarts due to Low Swap space because it loses its work process queue.

How do I adjust the swap space available to the App Service?

Answer 2

TP 125.8K Volunteer Moderator

Hi,

Please test with B3 instance to see if the issue is resolved. With default container B3 has 4 GiB swap space and 7 GiB RAM as compared to 2 GiB swap space and 3.5 GiB RAM with B2 instance.

Are you using custom container for your app? If yes, how did you create it?

Please click Accept Answer if the above was useful.

Thanks.

-TP

Porpoise 0 Reputation points

2023-07-17T18:15:38.96+00:00

I'll try B3, but was hoping I wouldn't have to pay more for a higher instance. This is just for development too. I will try it out.

Yes, it's a custom docker container image that hosts a basic python FastAPI app to process some documents. Created it with standard Dockerfile and pushed the image to ACR.
Porpoise 0 Reputation points

2023-07-17T18:18:07.3433333+00:00

Also, I would expect that since there's still so much memory to use, it wouldn't need to use swap space.
TP 125.8K Reputation points Volunteer Moderator

2023-07-17T18:38:53.66+00:00

@Porpoise I understand in regards to wanting to run it on lower instance for cost reasons. Give the B3 a try now to see if that makes any difference in your results, and if that fixes it perhaps we can get it working on lower instance.
Porpoise 0 Reputation points

2023-07-19T09:15:35.2+00:00

So far it's working ok but there are times memory goes up to 100% but so far no resets yet. But I haven't done enough testing or load testing. If more requests come in how do I know if it'll max out the swap space.
ajkuma 28,036 Reputation points Microsoft Employee Moderator

2023-07-28T13:29:24.8466667+00:00

As TP mentioned with memory and swap space more in B3 compared to B2.

Troubleshoot performance degradation is good place to configure application insights and monitoring your application.

If the issue reoccurs, we may need to dig deeper into the underlying root cause.

https://learn.microsoft.com/troubleshoot/azure/app-service/capture-memory-dumps-app-service#excessive-memory-consumption-scenario

Just sharing more info for some of the techniques and FAQs to handle resource -memory and storage related issues are covered in this doc scenario.

How to troubleshoot instance-related issues on Azure App Service -This video helps you to identify such issues, and explains how to resolve them. From improving load balancing to moving to an entirely new set of instances, you'll be well equipped to resolve instance-related issues by applying these techniques.

Additionally, The Ultimate Guide to Running Healthy Apps in the Cloud : To avoid a single point-of-failure, run your app with at least 2-3 instances. You can also configure rules to automatically scale out based on predefined rules such as: Resource utilization (memory, CPU, etc.)
James Robert Ayento 0 Reputation points

2023-09-26T04:23:45.8266667+00:00

Where to find the swap space for B1 instance?

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App Service Linux restarted due to low swap space

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