LoadBalancer

This guide covers how to get service of type LoadBalancer working in a kind cluster using Metallb.

This guide complements MetalLB installation docs, and sets up MetalLB using layer2 protocol. For other protocols check MetalLB configuration docs.

With Docker on Linux, you can send traffic directly to the loadbalancer’s external IP if the IP space is within the docker IP space.

On macOS and Windows, docker does not expose the docker network to the host. Because of this limitation, containers (including kind nodes) are only reachable from the host via port-forwards, however other containers/pods can reach other things running in docker including loadbalancers. You may want to check out the Ingress Guide as a cross-platform workaround. You can also expose pods and services using extra port mappings as shown in the extra port mappings section of the Configuration Guide.

Installing MetalLB using default manifests 🔗︎

Apply MetalLB manifest 🔗︎

Since version 0.13.0, MetalLB is configured via CRs and the original way of configuring it via a ConfigMap based configuration is not working anymore.

kubectl apply -f https://raw.githubusercontent.com/metallb/metallb/v0.13.7/config/manifests/metallb-native.yaml

Wait until the MetalLB pods (controller and speakers) are ready:

kubectl wait --namespace metallb-system \ --for=condition=ready pod \ --selector=app=metallb \ --timeout=90s

Setup address pool used by loadbalancers 🔗︎

To complete layer2 configuration, we need to provide MetalLB a range of IP addresses it controls. We want this range to be on the docker kind network.

docker network inspect -f '{{.IPAM.Config}}' kind

If you are using podman 4.0 or higher in rootful mode with the netavark network backend, use the following command instead:

podman network inspect -f '{{range .Subnets}}{{if eq (len .Subnet.IP) 4}}{{.Subnet}}{{end}}{{end}}' kind

The output will contain a cidr such as 172.19.0.0/16. We want our loadbalancer IP range to come from this subclass. We can configure MetalLB, for instance, to use 172.19.255.200 to 172.19.255.250 by creating the IPAddressPool and the related L2Advertisement.

apiVersion: metallb.io/v1beta1
kind: IPAddressPool
metadata:
  name: example
  namespace: metallb-system
spec:
  addresses:
  - 172.19.255.200-172.19.255.250
---
apiVersion: metallb.io/v1beta1
kind: L2Advertisement
metadata:
  name: empty
  namespace: metallb-system

Apply the contents

kubectl apply -f https://kind.sigs.k8s.io/examples/loadbalancer/metallb-config.yaml

Using LoadBalancer 🔗︎

The following example creates a loadbalancer service that routes to two http-echo pods, one that outputs foo and the other outputs bar.

kind: Pod
apiVersion: v1
metadata:
  name: foo-app
  labels:
    app: http-echo
spec:
  containers:
  - name: foo-app
    image: hashicorp/http-echo:0.2.3
    args:
    - "-text=foo"
---
kind: Pod
apiVersion: v1
metadata:
  name: bar-app
  labels:
    app: http-echo
spec:
  containers:
  - name: bar-app
    image: hashicorp/http-echo:0.2.3
    args:
    - "-text=bar"
---
kind: Service
apiVersion: v1
metadata:
  name: foo-service
spec:
  type: LoadBalancer
  selector:
    app: http-echo
  ports:
  # Default port used by the image
  - port: 5678

Apply the contents

kubectl apply -f https://kind.sigs.k8s.io/examples/loadbalancer/usage.yaml

Now verify that the loadbalancer works by sending traffic to it’s external IP and port.

LB_IP=$(kubectl get svc/foo-service -o=jsonpath='{.status.loadBalancer.ingress[0].ip}')

# should output foo and bar on separate lines 
for _ in {1..10}; do
  curl ${LB_IP}:5678
done