MetalLB configuration guidelines for subnets

Each Subnet object can define either a MetalLB address range or MetalLB address pool. A MetalLB address pool may contain one or several address ranges. The following rules apply to creation of address ranges or pools:

  • To designate a subnet as a MetalLB address pool or range, use the ipam/SVC-MetalLB label key. Set the label value to "1".

  • The object must contain the cluster.sigs.k8s.io/<cluster-name> label to reference the name of the target cluster where the MetalLB address pool is used.

  • You may create multiple subnets with the ipam/SVC-MetalLB label to define multiple IP address ranges or multiple address pools for MetalLB in the cluster.

  • The IP addresses of the MetalLB address pool are not assigned to the interfaces on hosts. This subnet is virtual. Do not include such subnets to the L2 template definitions for your cluster.

  • If a Subnet object defines a MetalLB address range, no additional object properties are required.

  • You can use any number of Subnet objects that define a single MetalLB address range. In this case, all address ranges are aggregated into a single MetalLB L2 address pool named services having the auto-assign policy enabled.

  • Intersection of IP address ranges within any single MetalLB address pool is not allowed.

    The bare metal provider verifies intersection of IP address ranges. If it detects intersection, the MetalLB configuration is blocked and the provider logs contain corresponding error messages.

Use the following labels to identify the Subnet object as a MetalLB address pool and configure the name and protocol for that address pool. All labels below are mandatory for the Subnet object that configures a MetalLB address pool.

Mandatory Subnet labels for a MetalLB address pool

Label

Description

Labels to link Subnet to the target cluster and region

cluster.sigs.k8s.io/cluster-name

Specifies the cluster name where the MetalLB address pool is used.

kaas.mirantis.com/region

Specifies the region name of the cluster where the MetalLB address pool is used.

kaas.mirantis.com/provider

Specifies the provider of the cluster where the MetalLB address pool is used.

ipam/SVC-MetalLB

Defines that the Subnet object will be used to provide a new address pool or range for MetalLB.

metallb/address-pool-name

Every address pool must have a distinct name.

The services-pxe address pool is mandatory when configuring a dedicated PXE network in the management cluster. This name will be used in annotations for services exposed through the PXE network.

metallb/address-pool-auto-assign

Configures the auto-assign policy of an address pool. Boolean.

Caution

For the address pools defined using the MetalLB Helm chart values in the Cluster spec section, auto-assign policy is set to true and is not configurable.

For any service that does not have a specific MetalLB annotation configured, MetalLB allocates external IPs from arbitrary address pools that have the auto-assign policy set to true.

Only for the service that has a specific MetalLB annotation with the address pool name, MetalLB allocates external IPs from the address pool having the auto-assign policy set to false.

metallb/address-pool-protocol

Sets the address pool protocol. The only supported value is layer2 (default).

Caution

Do not set the same address pool name for two or more Subnet objects. Otherwise, the corresponding MetalLB address pool configuration fails with a warning message in the bare metal provider log.

Caution

For the auto-assign policy, the following configuration rules apply:

  • At least one MetalLB address pool must have the auto-assign policy enabled so that unannotated services can have load balancer IPs allocated for them. To satisfy this requirement, either configure one of address pools using the Subnet object with metallb/address-pool-auto-assign: "true" or configure address range(s) using the Subnet object(s) without metallb/address-pool-* labels.

  • When configuring multiple address pools with the auto-assign policy enabled, keep in mind that it is not determined in advance which pool of those multiple address pools is used to allocate an IP for a particular unannotated service.