# MetalLB — Load Balancer Implementation for Bare-Metal Kubernetes

> MetalLB is a network load-balancer implementation for bare-metal Kubernetes clusters using standard routing protocols (Layer 2 ARP/NDP or BGP). It lets Services of type LoadBalancer work on clusters that do not run on a cloud provider.

## Install

Save as a script file and run:

# MetalLB — Bare-Metal LoadBalancer for Kubernetes

## Quick Use
```bash
# Install MetalLB
kubectl apply -f \
  https://raw.githubusercontent.com/metallb/metallb/v0.14.8/config/manifests/metallb-native.yaml

# Configure an IP pool (L2 mode)
cat <<EOF | kubectl apply -f -
apiVersion: metallb.io/v1beta1
kind: IPAddressPool
metadata: { name: default, namespace: metallb-system }
spec: { addresses: [ 192.168.1.240-192.168.1.250 ] }
---
apiVersion: metallb.io/v1beta1
kind: L2Advertisement
metadata: { name: default, namespace: metallb-system }
EOF

# Expose a Service
kubectl expose deploy nginx --type=LoadBalancer --port=80
```

## Introduction
Outside a cloud, Kubernetes Services of type `LoadBalancer` stay in the `Pending` state because there is no cloud controller to allocate an external IP. MetalLB fills that gap with a small set of Kubernetes-native components that advertise Service IPs to the local network either by ARP/NDP or BGP, giving on-prem clusters the same ergonomics as EKS or GKE.

## What MetalLB Does
- Allocates IPs from administrator-defined pools to LoadBalancer Services
- Advertises those IPs using Layer 2 (ARP/NDP) or Layer 3 (BGP)
- Integrates with your existing network routers for session-aware failover
- Supports IPv4 and IPv6 pools, including dual-stack Services
- Runs entirely as pods; no changes to the cluster data plane are required

## Architecture Overview
MetalLB ships two Deployments: a controller that watches Services and assigns IPs, and a DaemonSet speaker that advertises assigned IPs from each node. In L2 mode, one speaker becomes the elected "owner" of a Service IP and responds to ARP/NDP queries. In BGP mode, every speaker peers with upstream routers so traffic can be ECMP-balanced across all nodes. Configuration is entirely CRD-driven (IPAddressPool, L2Advertisement, BGPAdvertisement, BGPPeer).

## Self-Hosting & Configuration
- Install via FRRouting-based manifests for BGP or native manifests for L2-only
- Define `IPAddressPool` resources per subnet or tenant
- Use `BGPPeer` + `BGPAdvertisement` for advanced routing with communities and local-pref
- Configure `memberlist` secret to prevent cross-cluster speaker collisions
- Validate with `kubectl describe service` — the `LoadBalancer Ingress` field should show the allocated IP

## Key Features
- Two modes: L2 (zero-config, single active node) and BGP (ECMP across all nodes)
- IPv6 and dual-stack support
- Fine-grained pool scoping via namespace and Service selectors
- FRR integration unlocks BFD, communities and unnumbered peering
- Prometheus metrics and events for every allocation and advertisement

## Comparison with Similar Tools
- **kube-vip** — combines VIP + control-plane HA; simpler but less BGP-friendly
- **PureLB** — MetalLB fork with a different allocator model
- **Cilium LB IPAM** — built into Cilium; requires the Cilium data plane
- **Calico LoadBalancer** — ships with Calico BGP; overlaps with MetalLB BGP mode
- **External hardware LBs (F5, A10)** — powerful but expensive and out-of-cluster

## FAQ
**Q:** Does L2 mode balance traffic across nodes?
A: No. In L2 mode a single node answers ARP for each VIP. For active/active balancing use BGP.

**Q:** Can I mix IPv4 and IPv6 pools?
A: Yes. Create separate pools per family and MetalLB will assign a VIP to each Service that requests it.

**Q:** What happens if I run MetalLB alongside a cloud controller?
A: Typically the cloud provider handles the `LoadBalancer` type; you can set `loadBalancerClass` so MetalLB only touches Services it owns.

**Q:** Is BGP mode production ready?
A: Yes, including FRR-based peering, BFD and multi-hop. Many telcos and on-prem shops run it in production.

## Sources
- https://github.com/metallb/metallb
- https://metallb.universe.tf

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Source: https://tokrepo.com/en/workflows/fd41c4ac-38e6-11f1-9bc6-00163e2b0d79
Author: Script Depot