Skip to content

MetalLB: Self-hosted Load Balancers for Kubernetes

Introduction

MetalLB hooks into your Kubernetes cluster, and provides a network load-balancer implementation. In short, it allows you to create Kubernetes services of type LoadBalancer in clusters that don’t run on a cloud provider, and thus cannot simply hook into paid products to provide load balancers.

Kubernetes does not offer an implementation of network load balancers (Services of type LoadBalancer) for bare-metal clusters. The implementations of network load balancers that Kubernetes does ship with are all glue code that calls out to various IaaS platforms (GCP, AWS, Azure…). If you’re not running on a supported IaaS platform (GCP, AWS, Azure…), LoadBalancers will remain in the “pending” state indefinitely when created.

Bare-metal cluster operators are left with two lesser tools to bring user traffic into their clusters, “NodePort” and “externalIPs” services. Both of these options have significant downsides for production use, which makes bare-metal clusters second-class citizens in the Kubernetes ecosystem.

MetalLB aims to redress this imbalance by offering a network load balancer implementation that integrates with standard network equipment, so that external services on bare-metal clusters also “just work” as much as possible.

Installation

Installing MetalLB is pretty straightforward with Helm:

1
2
helm repo add metallb https://metallb.github.io/metallb
helm install metallb metallb/metallb -n kube-system --wait

Configuration

We'll take a look here at the Layer 2 configuration, similar to VRRP and Keepalived.

Create a pool of IP addresses for the load balancers:

1
2
3
4
5
6
7
8
9
apiVersion: metallb.io/v1beta1
kind: IPAddressPool
metadata:
name: metallb-pool
namespace: kube-system
spec:
# 50 available IPs for the load balancers
addresses:
  - 192.168.0.1-192.168.0.50

Then create a layer 2 configuration:

1
2
3
4
5
6
7
8
apiVersion: metallb.io/v1beta1
kind: L2Advertisement
metadata:
name: l2-advertisement
namespace: kube-system
spec:
ipAddressPools:
  - metallb-pool

Then apply the configuration:

1
kubectl apply -f ipaddresspool.yaml -f l2advertisement.yaml

Usage

Now when you want to ask for a load balancer, you need to use an annotation to tell MetalLB to use the load balancer. You need to set also the IP you want to use for the load balancer. Here is an example to add in a service:

1
2
3
4
5
service:
  enabled: true
  externalTrafficPolicy: Local
  annotations:
    metallb.universe.tf/loadBalancerIPs: 192.168.0.1