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I'm new to DevOps work and am having a though time figuring out how the whole final architecture should look like. My project currently runs on a single Kubernetes Cluster and a single node with a single pod, in the very common Nginx reverse proxy + UWSGI Django app. I have to implement a scaling architecture. My understanding is that I should use an Ingress Controller behind a LoadBalancer (I'm hosted at OVH, they do provide a built-in LoadBalancer). The Ingress Controller will then distribute the traffic to my pods.

Question 1: if my Django app listens on port 8000, setting ReplicaSet to 2 does not work because the port is already taken. This makes me believe I'm only supposed to have one pod per node but some information says otherwise. How can I run multiple replicas on the same node?

Question2: let's say I deploy 9 more nodes. Should all my 10 nodes be behind 1 Ingress Controller (and 1 Load Balancer) or should each node have its own Ingress Controller ?

Question3: if I have only one Ingress Controller, the Load Balancer does not really "balance" any load, its sole purpose is to expose my service to the Internet, is that normal?

Question4: what happens when the Ingress Controller is overloaded? Do I duplicate everything and then the Load Balancer distributes the requests on the 2 Controllers?

This and this is a good starting point, but still does not answer my questions directly.

mrj
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1 Answers1

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  1. Every pod has its own networking setup so two replicas (i.e. two pods) can both listen on the same port. Unless you've enabled host networking mode which should not be used here.

  2. Not directly, the ingress controller can be a lot of things. If you're using a self-hosted one (I see the ingress-nginx tag so assuming you are using that) then each controller replica is an independent copy of the proxy setup. You would want 2 at least for redundancy but unless you need to break up your traffic because those two can't keep up with it (would have to be truly huge request volume) that's probably all you need.

  3. Yes, that's fine on the K8s side, though as mentioned if you have multiple nodes available you probably want at least two ingress controller replicas in case one node dies unexpectedly.

  4. The edge LoadBalancer is round-robin-ing requests between all the nginx proxy instances so if you need more capacity you would spawn more replicas (assuming you have spare CPU on the cluster, if not then more nodes first then more replicas).

coderanger
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  • 4. When you say "The edge LoadBalancer is round-robin-ing requests between all the nginx proxy instances", you mean Nginx ingress controllers? That also means that another Nginx proxy behind the Nginx ingress controller is redundant and should be removed, right? – mrj May 17 '21 at 10:36
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    No, I'm talking about the ingress-nginx controller pods. Those are each an nginx proxy. – coderanger May 17 '21 at 17:03
  • Your answers @corderanger have been very, very helpful, thank you very much!!! Finding global architecture information (beginner level) to understand the big picture has been surprisingly difficult. – mrj May 17 '21 at 20:33