What’s a LoadBalancer?

One of the first things you might run into after building a new Kubernetes cluster is that as soon as you go to build something that has a LoadBalancer type service, it’s stuck in a Pending status. That’s because you don’t have a “controller” (is that the right term?) to handle this type of service. It’s not included out of the box.

Why not include LoadBalancer out of the box? Because it requires some environment specific configuration, and most importantly in our case that’s a pool of IP addresses that are dedicated for this purpose. So how do we tell Kubernetes what IPs it can use for LoadBalancer services? MetalLB - https://metallb.io/

There are other options such as KubeVIP (https://kube-vip.io/), which is also a great project. I’m going to use MetalLB because that’s what I have already figured out. You could even use KubeVIP as a control plane load balancer, in addition to MetalLB as a service load balancer. One is dedicated to load balancing the control plane, which means you can set one IP address for all 3 control plane nodes as an interface between kubectl and your cluster’s API. But what we’re focused on here is Service load balancing, so the same thing but for all the stuff you’re actually running on your cluster like websites, etc. And eventually this will tie into Ingress and Gateway API, but let’s not get too far into the weeds yet.

See For Yourself

If you want to see the behavior wen you create a LoadBalancer service without something that implements this type of service such as MetalLB, follow along. The symptom is that instead of getting an IP assigned, you will see the EXTERNAL-IP “stuck” as <pending>.

• Save this as test-lb-svc.yaml and then run kubectl apply -f test-lb-svc.yaml. This creates a deployment running 2 replicas of nginx, then creates a LoadBalancer service in front of it.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:latest
        ports:
        - containerPort: 80
---
apiVersion: v1
kind: Service
metadata:
  name: nginx-loadbalancer
spec:
  type: LoadBalancer
  selector:
    app: nginx
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80

• Check the service status with kubectl get svc and look at the EXTERNAL-IP for the nginx-loadbalancer service. Notice the <pending> instead of an actual IP address:

NAME                 TYPE           CLUSTER-IP      EXTERNAL-IP   PORT(S)        AGE
kubernetes           ClusterIP      10.96.0.1       <none>        443/TCP        40h
nginx-loadbalancer   LoadBalancer   10.99.103.170   <pending>     80:30652/TCP   3s

• You can delete this and try again later after deploying MetalLB, or leave it and it will automatically get an IP assigned by MetalLB once it’s running.

MetalLB Setup

Elaborate…