ssl - How NGINX Ingress controller back-end protocol annotation works in path based routing?

Question

I'm currently playing with NGINX ingress controller in my k8s cluster. I was trying to make end-to-end encryption work and I was able to make the connection secure all the way to the pod.

In order to achieve HTTPS all the way till pod, I had to use annotation

nginx.ingress.kubernetes.io/backend-protocol: "HTTPS"

Sample Ingress:

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: foo-api-ingress
  annotations:
    kubernetes.io/ingress.class: "nginx"
    nginx.ingress.kubernetes.io/backend-protocol: "HTTPS"
spec:
  tls:
  - hosts:
    - foo.example.com
    secretName: foo-cert
  rules:
  - host: foo.example.com
    http:
      paths:
      - path: /path1
        backend:
          serviceName: foo-api-path1-service
          servicePort: 443
      - path: /path2
        backend:
          serviceName: foo-api-path2-service
          servicePort: 443

I'm confused in terms of how exactly this happens because when we encrypt the connection path also get encrypted then how NGINX does path-based routing? does it decrypt the connection at ingress and re-encrypt it? also, does performance get affected by using this method?

Answer 1

TL;DR

does it decrypt the connection at ingress and re-encrypt it?

In short, yes. Please see the explanation below.

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Explanation

The path that a request is travelling to get to a Pod can be seen as:

• Kubernetes.io: Docs: Concepts: Services networking: Ingress

Assuming that we have an Ingress controller (nginx-ingress) in place of an Ingress you can have several ways to connect your client with a Pod (simplified):

• Unencrypted:
  • client -- (HTTP) --> Ingress controller -- (HTTP) --> Service ----> Pod

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• Encrypted at the Ingress controller (with nginx.ingress.kubernetes.io/backend-protocol: "HTTPS")
  • client -- (HTTP) --> Ingress controller -- (HTTPS) --> Service ----> Pod

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• Encrypted and decrypted at the Ingress controller where TLS Termination happens:
  • client -- (HTTPS) --> Ingress controller (TLS Termination) -- (HTTP) --> Service ----> Pod

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Your setup:

• Encrypted and decrypted at the Ingress controller where TLS Termination happens and encrypted once again when connecting with a HTTPS backend by nginx.ingress.kubernetes.io/backend-protocol: "HTTPS":
  • client -- (HTTPS) --> Ingress controller (TLS Termination) -- (HTTPS) --> Service ----> Pod

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• Encrypted and decrypted at the Pod where Ingress controller is configured with SSL Passthrough:
  • client -- (HTTPS) --> Ingress controller -- (HTTPS) --> Service ----> Pod

Disclaimer!

This is only a simplified explanation. For more reference you can look at this comment:

there is a missing detail here, the SSL Passthrough traffic never reaches NGINX in the ingress controller. There is a go listener for TLS connections that just pipes the traffic to the service defined in the ingress.

• Github.com: Kubernetes: Ingress nginx: Issues: 5618

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For more reference you can look on the similar question (with an answer):

• Stackoverflow.com: Answer: How to configure ingress to direct traffic to an https backend using https

You can also check this article with example setup similar to yours:

• Code.oursky.com: How to enable tls https between your kubernetes ingress and back end deployments

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Additional resources:

• Github.com: Kubernetes: Ingress nginx: Is it possible to have secure backend connections from the nginx controller?
• Github.com: Kubernetes: Ingress nginx: Nginx configuration: Annotations: Backend certificate authentication