It’s very very easy to use Kubernetes(K8s) to provision an external service with AWS ELB, there’s one catch though(at least for now in 2018).
AWS ELB is usually used with an auto scaling group and a launch configuration. However with K8s, EC2 instances won’t get spun directly, only pods will, which is call Horizontal Scaling. K8s will issue AWS API calls to update the ELBs so there’s no need for auto scaling groups or launch configurations.
This worked like a charm until when things got busy. There was a brief down time on one of the ELBs managed by K8s, because all instances at the back of the ELB were marked as unhealthy! Of course they were healthy at that moment. With help from AWS Support team, the culprit seems to be similar to this case: https://github.com/kubernetes/kubernetes/issues/47067.
Luckily for me, I had a gut feel that the simple ELB implementation isn’t the best practice and started to adopt the K8s Ingress Controller. And in this case I believe ingress can avoid the down time because the routing is done internally in K8s cluster which doesn’t involving AWS API calls. Nonetheless ingress can use 1 ELB for many apps and that’s good because ELBs are expensive.
Here are steps to deploy an nginx ingress controller as an http(L7) load balancer:
Deploy the mandatory schema, the default replica number for the controller is 2, I changed it to 3 to have 1 in each availability zone:
kubectl apply -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/master/deploy/mandatory.yaml
Some customisation for L7 load balancer on AWS, remember to use your SSL cert if you need https termination:
kubectl apply -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/master/deploy/provider/aws/service-l7.yaml
kubectl apply -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/master/deploy/provider/aws/patch-configmap-l7.yaml
Then an ingress for an app can be deployed:
$ cat .k8s/prod/ingress.yaml
- host: my.domain.elb
- path: /
- host: my.domain.cdn
- path: /
- my-service is a common NodePort service and has port 80 exposed
- io/ingress.class is for multiple ingress controllers in same k8s cluster, eg. 1 for dev and the other for prod
- for now I have to duplicate the host block for each domain, because wildcard or regex are not supported by k8s ingress specification
- at last, find the ELB this ingress controller created, then point my.domain.elb to it, then the CDN domain can use my.domain.elb as origin.