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metallb

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MetalLB

MetalLB is a load-balancer implementation for bare metal Kubernetes clusters, using standard routing protocols.

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.

Requirements

MetalLB requires the following to function:

  • A Kubernetes cluster, running Kubernetes 1.13.0 or later, that does not already have network load-balancing functionality.
  • A cluster network configuration that can coexist with MetalLB.
  • Some IPv4 addresses for MetalLB to hand out.
  • When using the BGP operating mode, you will need one or more routers capable of speaking BGP.
  • When using the L2 operating mode, traffic on port 7946 (TCP & UDP, other port can be configured) must be allowed between nodes, as required by memberlist.

Installation

To install MetalLB, apply the manifest:

kubectl apply -f https://raw.githubusercontent.com/metallb/metallb/v0.15.3/config/manifests/metallb-native.yaml

Please do note that these manifests deploy MetalLB from the main development branch. We highly encourage cloud operators to deploy a stable released version of MetalLB on production environments!

This will deploy MetalLB to your cluster, under the metallb-system namespace. The components in the manifest are:

  • The metallb-system/controller deployment. This is the cluster-wide controller that handles IP address assignments.
  • The metallb-system/speaker daemonset. This is the component that speaks the protocol(s) of your choice to make the services reachable.
  • Service accounts for the controller and speaker, along with the RBAC permissions that the components need to function.

The installation manifest does not include a configuration file. MetalLB’s components will still start, but will remain idle until you start deploying resources.

Usage

IP Claims

In order for the Load Balancer to hand out IPs, you first need to assign an IP range and interfaces which broadcast them:

apiVersion: metallb.io/v1beta1
kind: IPAddressPool
metadata:
  name: hydra-ip-pool
  namespace: metallb-system
spec:
  addresses:
  - 192.168.2.200-192.168.2.220
---
apiVersion: metallb.io/v1beta1
kind: L2Advertisement
metadata:
  name: l2
  namespace: metallb-system
spec:
  interfaces:
  - ens18
  - end0

LoadBalancer Services

To expose an application using the MetalLB LoadBalancer, you can create a Service of type LoadBalancer.

apiVersion: v1
kind: Service
metadata:
  name: nginx-loadbalancer
  namespace: default
spec:
  selector:
    app: nginx
  type: LoadBalancer
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80

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