MetalLB configuration reference for Lokomotive

Introduction

MetalLB is a load balancer implementation for bare metal Kubernetes clusters, using standard routing protocols. It allows using Kubernetes Service of type LoadBalancer on an infrastructure without native load balancing support.

On IaaS providers such as AWS or GCP, creating a Kubernetes Service of type LoadBalancer triggers an automatic creation of a provider-specific load balancer which routes traffic to the Kubernetes service. However, when running Kubernetes on bare metal environments such as Packet , which typically don’t provide native load balancer support, creating a LoadBalancer Service would result in the service staying forever in the Pending state since no load balancer is created by the infrastructure provider. MetalLB helps solve this problem by creating a “virtual” load balancer for each LoadBalancer service. It does so using standard network protocols such as BGP and ARP.

Prerequisites

A Lokomotive cluster accessible via kubectl deployed on Packet.
A compatible cluster networking addon.
At least one IPv4 address pool for MetalLB to allocate - one address is needed per LoadBalancer service.
One or more routers capable of speaking BGP.

Configuration

MetalLB can operate in two modes: BGP and layer 2. This component currently supports only the BGP mode.

MetalLB operates by allocating one IPv4 address to each service of type LoadBalancer created on the cluster. It then advertises this address to one or more upstream BGP routers. This enables both high availability and load balancing: high availability is achieved since BGP naturally converges upon node failure, and load balancing is achieved using ECMP .

MetalLB component configuration example:

component "metallb" {
  address_pools = {
    pool1 = ["147.63.8.20/32"]
    pool2 = ["147.85.47.16/29", "147.85.47.24/29"]
  }
  controller_node_selectors = {
    "kubernetes.io/hostname" = "worker3"
  }
  speaker_node_selectors = {
    "ingress_node" = "true"
    "node-role.kubernetes.io/node" = ""
  }
  speaker_toleration {
    key = "speaker_key1"
    operator = "Equal"
    value = "value1"
  }
  controller_toleration {
    key = "controller_key1"
    operator = "Equal"
    value = "value1"
  }
  # If true, then Prometheus Operator component should be installed.
  service_monitor = true
}

MetalLB will use the specified CIDR for exposing services of type LoadBalancer.

Advanced IP allocation

By default, MetalLB uses all specified address pools to allocate IP addresses to services. To request an address from a specific pool, set the metallb.universe.tf/address-pool annotation for the relevant service:

apiVersion: v1
kind: Service
metadata:
  name: nginx
  annotations:
    metallb.universe.tf/address-pool: pool2
spec:
  ports:
  - port: 80
    targetPort: 80
  selector:
    app: nginx
  type: LoadBalancer

Attribute reference

Table of all the arguments accepted by the component.

Argument	Description	Default	Type	Required
`address_pools`	A map which allows specifying one or more CIDRs which MetalLB can use to expose services.	-	map(list(string))	true
`controller_node_selectors`	A map with specific labels to run MetalLB controller pods selectively on a group of nodes.	-	map(string)	false
`speaker_node_selectors`	A map with specific labels to run MetalLB speaker pods selectively on a group of nodes.	-	map(string)	false
`controller_toleration`	Specify one or more tolerations for controller pods.	-	list(object({key = string, effect = string, operator = string, value = string, toleration_seconds = string }))	false
`speaker_toleration`	Specify one or more tolerations for speaker pods.	-	list(object({key = string, effect = string, operator = string, value = string, toleration_seconds = string }))	false
`service_monitor`	Create ServiceMonitor for Prometheus to scrape MetalLB metrics.	false	bool	false

Applying

To apply the MetalLB component:

lokoctl component apply metallb

Deleting

To destroy the component:

lokoctl component delete metallb --delete-namespace