Mutithreading in Azure Container Apps & Container CPU Cores

Question

Mutithreading in Azure Container Apps & Container CPU Cores

Martin Kaiser 16

Hello,

I'm getting an application ready for a production release in Azure Container Apps and I'm trying to do some multithreading optimization but I've been a bit confused as to how many CPU cores a single container instance/replica has access to. I've been setting my Azure Container Apps scale core limit per instance between 1-2 cores, then doing some load testing on the API and monitoring top in one or more instance. The odd thing I've found is that top and lscpu seem to list the cores available as 4 most of the time, but sometimes it will list 8 cores available. I can't seem to figure out what determines the count between 4 and 8. Scaling doesn't seem to be the factor, it almost seems random.

Does anyone know how the cores work inside the container itself, and how best to optimize for mutlithreading? My application can use as many cores as it's given, but I'd like to make sure I'm putting a limit on that to get the fastest response time and have consistency across all the replicas, especially since we can scale the app horizontally anyways.

I've thought about trying to set --cpus in the Docker image to see what happens but figured it was worth asking the community before I spend the time and money re-running the load tests.

Thanks

MuthuKumaranMurugaachari-MSFT 22,451 Reputation points Moderator

2023-12-18T14:52:40.1066667+00:00

Martin Kaiser Thanks for posting your question in Microsoft Q&A. If you are looking for cores limit like replicas in Azure Container Apps, checkout Quotas for Azure Container Apps doc and the limit is based on workload profiles. If your business scenario requires increase in quota, you can also submit it via how to request a limit increase.

Can you clarify how you are setting up the limit in your apps (like Configuration)?
Martin Kaiser 16 Reputation points

2023-12-18T17:04:05.68+00:00

Thanks Muthu,

I have read through the documentation but it only mentions the vCores and not the actual cores the application can use within the container replica's. For example:

Our API has a 1.5 vCore and 3GB memory limit per container instance. But when I connect to one of the replica's vis the console and do top, then 1 to show the cores. I get this:

lscpu

You can see the application is registering 4 cores for use, which means the app can multithread on 4 cores/threads. I'm assuming 1.5 vCores is sort theoretically assiging the use of 1.5 cores physical cores, but the container apps is allowing the system to split that into 4 cores for the app to use.

Sometimes when I've been testing it shows up as 0-7 CPU cores, so I'm just trying to figure out the best way to setup multi-threading for the app. I.e should I let it only use 4 threads, or should I set 8.

Thanks again!
MuthuKumaranMurugaachari-MSFT 22,451 Reputation points Moderator

2023-12-19T15:41:05.9866667+00:00

Martin Kaiser Yes, you are right we publish vCores not actual cores. Can you elaborate more about the app, runtime, how you configure multithreading? That will be useful to understand the context more.