Affinity with the canary

This idea is based on:

https://medium.com/google-cloud/kubernetes-canary-deployments-for-mere-mortals-13728ce032fe
https://github.com/Telefonica/nginx-canary

What's the idea

To build a simple way of deploy some kind of canary with a consistent user experience on top of Kubernetes.

Goals

1. Allow a simple way of canary deployment with weights
2. Once the user accessed canary or stable keep her/him stuck to this deploy (consistent user experience)

Motivation

Despite the fact that tools already exist to perform canary each one has a drawback.

Basic K8s features to do canary (to have a lot of pods with stable and canary and load balance between them) it's not enaugh since it can't handle stickiness.

NGINX Ingress Controller can handle session affinity, on one hand, and canary, in the other. But it is hard (or impossible) to put both features to work toghether.

I think tools like istio and fabio (Consul) have the features to do this... but they are oversized to our needs.

The solution

This solution is built using a reverse proxy and a lua script to handle the canary and the cookies that allows the sticky session.

Basically this is it:

We have two versions for our app: stable and canary.

Despite the qty of pods each one has its own service on front of it.

On front of these services we add a reverse proxy. It will handle mainly two activities: look for the cookie and (if cookie does not exist) split traffic between stable and canary based on canary weight.

On front of the reverse proxy there is a service, which is hitted by the traffic from ingress controller.

How to implement the solution

Just edit these values in file affinity-with-the-canary.yaml:

    - name: BASE_SVC_URL
      value: ".canary.svc.cluster.local"
    - name: STABLE_SVC_NAME
      value: kubeapp-production-service
    - name: CANARY_SVC_NAME
      value: kubeapp-canary-service
    - name: CANARY_WEIGHT
      value: "0.5"
    - name: COOKIE_MAX_AGE
      value: "172800"

BASE_SVC_URL is composed of namespace (canary in the example) and the base url for your cluster (this is almost standard).

STABLE_SVC_NAME and CANARY_SVC_NAME are the name of your apps' services.

CANARY_WEIGHT is the weight, number between 0 and 1. If random number is less or equal to CANARY_WEIGHT the request is sent to canary.

COOKIE_MAX_AGE set the max-age for the cookie. (seconds)

Finally, deploy your reverse proxy and point your ingress controller to the nginxcan-service service.

Note: All this stuff must be deployed inside the same namespace.

Note: there is defined a standard dns resolver (kube-dns.kube-system.svc.cluster.local), if you do not use the standard you must change it.

How to deactivate canary

If you want to deactivate canary (because you have no canary, have problems with canary or whatever it be...) you can set CANARY_WEIGHT to 0 and deploy affinity-with-the-canary.

All requests, despite the cookie can be set to canary, will be redirected to stable (and cookie re set accordingly).

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Example

To see an explanation of the example on this solution please go here