Configuring services to use MetalLB

Request a specific IP address
Request an IP address from a specific pool
Accept any IP address
Share a specific IP address
Configuring a service with MetalLB

To ensure predictable network endpoints, control how MetalLB assigns IP addresses to services of type LoadBalancer. Requesting specific addresses or pools ensures that your applications receive valid IP assignments that align with your specific network addressing plan.

Request a specific IP address

To assign a specific, static IP address to a service, configure the spec.loadBalancerIP parameter in the service specification.

MetalLB attempts to assign the requested address from the configured address pools, ensuring that your service is reachable at a designated, static network endpoint. If the requested IP address is not within any range, MetalLB reports a warning.

Example service YAML for a specific IP address

apiVersion: v1
kind: Service
metadata:
  name: <service_name>
  annotations:
    metallb.io/address-pool: <address_pool_name>
spec:
  selector:
    <label_key>: <label_value>
  ports:
    - port: 8080
      targetPort: 8080
      protocol: TCP
  type: LoadBalancer
  loadBalancerIP: <ip_address>

If MetalLB cannot assign the requested IP address, the EXTERNAL-IP for the service reports <pending> and running oc describe service <service_name> includes an event like the following example:

Example event when MetalLB cannot assign a requested IP address

  ...
Events:
  Type     Reason            Age    From                Message
  ----     ------            ----   ----                -------
  Warning  AllocationFailed  3m16s  metallb-controller  Failed to allocate IP for "default/invalid-request": "4.3.2.1" is not allowed in config

Request an IP address from a specific pool

Example service YAML for an IP address from a specific pool

apiVersion: v1
kind: Service
metadata:
  name: <service_name>
  annotations:
    metallb.io/address-pool: <address_pool_name>
spec:
  selector:
    <label_key>: <label_value>
  ports:
    - port: 8080
      targetPort: 8080
      protocol: TCP
  type: LoadBalancer

If the address pool that you specify for <address_pool_name> does not exist, MetalLB attempts to assign an IP address from any pool that permits automatic assignment.

Accept any IP address

To automatically allocate IP addresses to services without manual specification, configure MetalLB address pools to permit automatic assignment. MetalLB dynamically assigns available addresses from these pools, ensuring seamless service deployment and network connectivity.

Example service YAML for accepting any IP address

apiVersion: v1
kind: Service
metadata:
  name: <service_name>
spec:
  selector:
    <label_key>: <label_value>
  ports:
    - port: 8080
      targetPort: 8080
      protocol: TCP
  type: LoadBalancer

To colocate multiple services on a single IP address, apply the metallb.io/allow-shared-ip annotation to your service specifications. Configuring this annotation authorizes MetalLB to assign the same IP to multiple services, enabling efficient address usage while distinguishing traffic by port.

By default, services do not share IP addresses.

apiVersion: v1
kind: Service
metadata:
  name: service-http
  annotations:
    metallb.io/address-pool: doc-example
    metallb.io/allow-shared-ip: "web-server-svc"
spec:
  ports:
    - name: http
      port: 80
      protocol: TCP
      targetPort: 8080
  selector:
    <label_key>: <label_value>
  type: LoadBalancer
  loadBalancerIP: 172.31.249.7
# ...
---
apiVersion: v1
kind: Service
metadata:
  name: service-https
  annotations:
    metallb.io/address-pool: doc-example
    metallb.io/allow-shared-ip: "web-server-svc"
spec:
  ports:
    - name: https
      port: 443
      protocol: TCP
      targetPort: 8080
  selector:
    <label_key>: <label_value>
  type: LoadBalancer
  loadBalancerIP: 172.31.249.7
# ...

where:

metallb.io/allow-shared-ip: Specifies the same value for the metallb.io/allow-shared-ip annotation. This value is referred to as the sharing key.
name.port: Specifies different port numbers for the services.
spec.selector: Specifies identical pod selectors if you must specify externalTrafficPolicy: local so the services send traffic to the same set of pods. If you use the cluster external traffic policy, then the pod selectors do not need to be identical.
spec.loadBalancerIP: Optional parameter. If you specify the three preceding items, MetalLB might colocate the services on the same IP address. To ensure that services share an IP address, specify the IP address to share.

By default, Kubernetes does not allow multiprotocol load balancer services. This limitation would normally make it impossible to run a service like DNS that needs to listen on both TCP and UDP. To work around this limitation of Kubernetes with MetalLB, create two services:

For one service, specify TCP and for the second service, specify UDP.
In both services, specify the same pod selector.
Specify the same sharing key and spec.loadBalancerIP value to colocate the TCP and UDP services on the same IP address.

Configuring a service with MetalLB

To expose an application to external network traffic, configure a load-balancing service. MetalLB assigns an external IP address from a configured address pool, ensuring that your application is reachable from outside the cluster.

Prerequisites

Install the OpenShift CLI (oc).
Install the MetalLB Operator and start MetalLB.
Configure at least one address pool.
Configure your network to route traffic from the clients to the host network for the cluster.

Procedure

Create a <service_name>.yaml file. In the file, set the spec.type parameter to LoadBalancer.

Refer to the examples for information about how to request the external IP address that MetalLB assigns to the service.

Create the service:

$ oc apply -f <service_name>.yaml

Example output

service/<service_name> created

Verification

Describe the service:

$ oc describe service <service_name>