Automatically set MetalLB IP Addresses with kind

kind doesn't come with a Load Balancer implementation by default. MetalLB seems like the most commonly used load balancer, but I have to look up how to configure it every time.

That is, until I saw an awesome docker network inspect | yq hack that I'm adding here for posterity.

First, install MetalLB:

bash
kubectl apply -f \
https://raw.githubusercontent.com/metallb/metallb/v0.13.10/config/manifests/metallb-native.yaml

Then extract the subnet from the kind network and use yq to set the spec.addresses value in the manifest before applying it:

js
echo "---
apiVersion: metallb.io/v1beta1
kind: IPAddressPool
metadata:
  name: example
  namespace: metallb-system
spec:
  addresses: [] # set by make target
---
apiVersion: metallb.io/v1beta1
kind: L2Advertisement
metadata:
  name: empty
  namespace: metallb-system
" | \
SUBNET=$(docker network inspect kind --format '{{ (index .IPAM.Config 0).Subnet }}') \
yq '(select(.kind == "IPAddressPool") | .spec.addresses[0]) = env(SUBNET)' | \
kubectl apply -f -

That's all! For a few more details, here's what gets returned by docker network inspect:

bash
❯ docker network inspect kind --format '{{ (index .IPAM.Config 0).Subnet }}'
172.18.0.0/16

And if I run kubectl get services we'll see an IP address of 172.18.0.0 which is in that range:

bash
❯ kubectl get services -n kong
NAME                                 TYPE           CLUSTER-IP      EXTERNAL-IP   PORT(S)                      AGE
kong-controller-validation-webhook   ClusterIP      10.96.92.13     <none>        443/TCP                      105s
kong-gateway-admin                   NodePort       10.96.124.129   <none>        8444:30735/TCP               105s
kong-gateway-proxy                   LoadBalancer   10.96.66.27     172.18.0.0    80:31884/TCP,443:31329/TCP   105s