Overview

MetalLB is a load-balancer implementation for bare-metal Kubernetes clusters. In Crater, it enables internal service exposure using Layer 2 (L2) mode, which is ideal for environments where nodes reside in the same subnet and can directly communicate—such as campus intranets.

Crater clusters are deployed in a private university network, where all nodes and user access points share a common Layer 2 domain. Hence, MetalLB is configured to allocate IPs from a reserved internal IP address pool, enabling services of type LoadBalancer to be exposed without relying on external cloud providers.

Key Features

• L2 (ARP/NDP) mode — simple and effective for intranet environments.
• Assigns static internal IPs to Kubernetes services.
• Integrates with services like Prometheus, Grafana, and Harbor.

Installation

MetalLB is installed via the official Helm chart.

1. Add Helm Repo

helm repo add metallb https://metallb.github.io/metallb
helm repo update

2. Install MetalLB

helm upgrade --install metallb metallb/metallb -n metallb-system --version v0.14.8 --create-namespace

Configuration

1. Create an IPAddressPool

Configure a pool of available intranet IPs that MetalLB can assign to services:

apiVersion: metallb.io/v1beta1
kind: IPAddressPool
metadata:
  name: intranet-pool
  namespace: metallb-system
spec:
  addresses:
    - 192.168.100.240-192.168.100.250  # Replace with your campus subnet range

2. Configure L2 Advertisement

Enable L2 broadcasting (ARP/NDP) for the IP pool:

apiVersion: metallb.io/v1beta1
kind: L2Advertisement
metadata:
  name: intranet-l2
  namespace: metallb-system
spec:
  ipAddressPools:
    - intranet-pool

Usage

Once installed, services of type LoadBalancer will be assigned IPs from the configured pool.

Example:

apiVersion: v1
kind: Service
metadata:
  name: crater-web
  namespace: crater-system
spec:
  type: LoadBalancer
  selector:
    app: crater-ui
  ports:
    - port: 80
      targetPort: 8080

MetalLB will automatically assign an IP (e.g. 192.168.100.241) from the defined pool.

You can view assigned IPs with:

kubectl get services -A -o wide

Best Practices

Reserve address pool in your DHCP server or avoid conflicts manually.

Ensure all cluster nodes are in the same L2 broadcast domain.

Avoid exposing services to the public Internet—MetalLB here is used strictly within the campus network.

• Crater combine with IngressClass for unified domain routing. *

References

• MetalLB