Supporting wildcard domains for TLS: Kubernetes Ingress on GKE - ssl

Question

I'm working on an application that deploys kubernetes resources dynamically, and I'd like to be able to provision a shared SSL certificate for all of them. At any given time, all of the services have the path *.*.*.example.com.
I've heard that cert-manager will provision/re-provision certs automatically, but I don't necessarily need auto-provisioning if its too much overhead. The solution also needs to be able to handle these nested url subdomains.
Any thoughts on the easiest way to do this?

Answer 1

Have a look at nginx-ingress, which is a Kubernetes Ingress Controller that essentially makes it possible to run Nginx reverse proxy/web server/load balancer on Kubernetes.
nginx-ingress is built around the Ingress resource. It will watch Ingress objects and manage nginx configuration in config maps. You can define powerful traffic routing rules, caching, url rewriting, and a lot more via the Kubernetes Ingress resource rules and nginx specific annotations.
Here's an example of an Ingress with some routing. There's a lot more you can do with this, and it does support wildcard domain routing.
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
annotations:
kubernetes.io/ingress.class: nginx
nginx.ingress.kubernetes.io/rewrite-target: /$1
cert-manager.io/cluster-issuer: letsencrypt-prod
name: my-ingress
spec:
rules:
- host: app1.domain.com
http:
paths:
- backend:
serviceName: app1-service
servicePort: http
path: /(.*)
- host: app2.sub.domain.com
http:
paths:
- backend:
serviceName: app2-service
servicePort: http
path: /(.*)
tls:
- hosts:
- app1.domain.com
secretName: app1.domain.com-tls-secret
- hosts:
- app2.sub.domain.com
secretName: app2.sub.domain.com-tls-secret
The annotations section is really important. Above indicates that nginx-ingress should manage this Ingress definition. This annotations section allows to specify additional nginx configuration, in the above example it specifies a url rewrite target that can be used to rewrite urls in the rule section.
See this community post for installing nginx-ingress on GKE.
You'll notice the annotations also have a cert manager specific annotation which, if installed will instruct cert manager to issue certificates based on the hosts and secrets defined under the tls section.
Using cert-manager in combination with nginx-ingress, which isn't that complicated, you can set up automatic certificate creation/renewals.
It's hard to know the exact nature of your setup with deploying dynamic applications. But some possible ways to achieve the configuration are:
Have each app define it's own Ingress with it's own routing rules and TLS configuration, which gets installed/updated each time your the application is deployed
Have an Ingress per domain/subdomain. You could then specify a wild card subdomain and tls section with routing rules for that subdomain
Or possibly you could have one uber Ingress which handles all domains and routing.
The more fine grained the more control, but a lot more moving parts. I don't see this as a problem. For the last two options, it really depends on the nature of your dynamic application deployments.