Is this necessary to have multiple processes / threads in a Kubernetes pod?

Question

I'm using uwsgi in a container hosted in a Kubernetes cluster. UWSGI supports a traditional master / slave architecture to provide a better availability for the application but my question is, should I even use this feature?

In other words, when I need more processes to handle and compute requests, should I increase the number of pods in the cluster or should I still use master / slave mode of UWSGI to respond to the requests?

I think if you increase the based on requests you get better performance — Mohammad Efazati, Aug 23 '17 at 17:17

score 9 · Accepted Answer · answered Aug 16 '17 at 05:45

Be conscious of having enough threads/processes/pods to maintain availability if your application blocks while serving each HTTP request (e.g. Django). There is going to be some pod startup time if you're using a horizontal pod autoscaler, and I found with a high traffic application I had much better availability with uwsgi and the application within each pod (same container), and a separate nginx pod doing reverse proxying and request pooling when all the uwsgi workers were busy.

YMMV but at the end of the day, availability is more important than sticking to the single process per pod rule of thumb. Just understand the downsides, such as less isolation between the processes within the same container. Logs are available on a per container basis, so there won't be isolation between anything in the same container using the built in kubectl logs functionality.

My +1. I do have the same feeling about uwsgi and Django. If it's blocking the HTTP request, you need to have more than one process IMO. — Afshin Mehrabani, Aug 16 '17 at 09:42

score 5 · Answer 2 · answered Aug 15 '17 at 15:41

5

Recommended way to manage this in Kubernetes is to increase the number of PODs based on the workload requirements.

answered Aug 15 '17 at 15:41

sfgroups

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Thanks. And it means there should be only one thread / process inside the container? – Afshin Mehrabani Aug 15 '17 at 16:47
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Yes, having only one process is the best practice for container. process can have multiple threads inside. – sfgroups Aug 15 '17 at 17:01

score 2 · Answer 3 · answered Aug 23 '17 at 19:58

We use a deployment model in which a django based app is served by gunicorn with couple of worker processes. We have further tried to scale this pod to 2-3 replicas and have seen performance improvements.

It's totally upto what works for your app.

Advantage of scaling pods is that you can configure it dynamically, hence not wasting resources.

Is this necessary to have multiple processes / threads in a Kubernetes pod?

3 Answers3