After learning how to build my first terrible website, in ye olden days, perhaps the second useful thing I ever really learned was to run multiple websites on a single server using Apache VirtualHosts. The novelty of being able to run more than one application on a server was among the earliest things I recall being excited about. Fast forward to the very different deployment environments we have available today, and I find myself excited about about the same basic kinds of things. Today I thought I would share how one can implement a concept similar to Apache's VirtualHosts across Namespaces in Kubernetes.
Note: I won't cover too much about networking in Kubernetes in this blog post, but I recommand Julia Evans' post titled Operating a Kubernetes Network, which is a good, alebit advanced, overview of some of the things going on in Kubernetes behind the scenes to make networking in Kubernetes "work."
The basic gist of what I was trying to accomplish was as follows: deploy multiple application stacks, each separated into a Kubernetes Namespaces unto itself, and mount those all under the same public IP. Exposing applications to "the outside world" is relatively simple, numerous blog posts, documentation, and Stack Overflow snippets demonstrate this. Segregating workloads into Namespaces seems to be less popular however.
The most important component for making applications "serve things" from a Kubernetes cluster is the Ingress Resource.
Well, that's not entirely true.
The most important component for making applications "serve things" from a Kubernetes cluster is the Ingress Controller.
Two things coarsely referred to as "Ingresses" in examples and blog posts, which typically never discussed Namespaces, made searching and understanding the bits of information I needed to understand, rather tricky. As @evnsio highlights: "Explaining Kubernetes ingress controllers is hard".
Deep within a GitHub issue, which has been lost to the sands of time in my browser history, a passing comment revealed what I had been misunderstanding: a Kubernetes cluster will have one Ingress Controller, but can have many Ingress Resources.
Instead of trying to deploy an Ingress Controller to each namespace along with
my application, this informed me that I only needed to deploy one controller,
and then add an Ingress Resource for each "VirtualHost" in my environment. I
was also confused by the Name-based virtual hosting
which uses a single
.yaml configuration to describe multiple hosts. I found
myself exploring how to dynamically generate a mega-yaml-configuration
including all my "virtual hosts" across Namespaces.
As luck would have it, this is completely unnecessary! The nginx Ingress Controller pays attention to the entire Kubernetes object space, not just its own Namespace, for Ingress Resources. In effect this means that any Ingress Resource, in any Namespace, is going to be picked up and for which nginx rules will be generated.
With this knowledge in hand, not only could I separate name-based virtual hosts
into their own Namespaces, with little bits of Ingress Resource configuration
as shown below. I could also use the same host name and different
paths across Namespaces. In essence, one Namespace could have an Ingress Resource
/, while another Namespace with its application stack,
might have an Ingress Resource mapping a
/blog. The one Ingress
Controller amagalmates those into a single nginx configuration to handle
Below is an example of an nginx Ingress Controller and a single Ingress Resource which is applied to a single Namespace.
apiVersion: extensions/v1beta1 kind: Ingress metadata: name: 'http-ingress' namespace: 'jenkins-rtyler' annotations: kubernetes.io/tls-acme: "true" kubernetes.io/ingress.class: "nginx" spec: tls: - hosts: - rtyler.codevalet.io secretName: ingress-tls rules: - host: 'rtyler.codevalet.io' http: paths: - path: '/' backend: serviceName: 'jenkins-rtyler' servicePort: 80
--- apiVersion: v1 kind: List items: - apiVersion: v1 kind: Namespace metadata: name: 'nginx-ingress' - apiVersion: v1 kind: Service metadata: name: 'nginx' namespace: 'nginx-ingress' spec: type: LoadBalancer ports: - port: 80 name: http - port: 443 name: https sessionAffinity: 'ClientIP' selector: app: 'nginx' - apiVersion: v1 kind: ConfigMap metadata: namespace: 'nginx-ingress' name: 'nginx' data: proxy-connect-timeout: "15" proxy-read-timeout: "600" proxy-send-timeout: "600" hsts-include-subdomains: "false" body-size: "64m" server-name-hash-bucket-size: "256" - apiVersion: extensions/v1beta1 kind: Deployment metadata: name: 'nginx' namespace: 'nginx-ingress' spec: replicas: 1 template: metadata: labels: app: 'nginx' spec: containers: - image: 'gcr.io/google_containers/nginx-ingress-controller:0.8.3' name: 'nginx' imagePullPolicy: Always env: - name: POD_NAME valueFrom: fieldRef: fieldPath: metadata.name - name: POD_NAMESPACE valueFrom: fieldRef: fieldPath: metadata.namespace livenessProbe: httpGet: path: /healthz port: 10254 scheme: HTTP initialDelaySeconds: 30 timeoutSeconds: 5 ports: - containerPort: 80 - containerPort: 443 args: - /nginx-ingress-controller - --default-backend-service=webapp/webapp - --nginx-configmap=nginx-ingress/nginx