Create an External Load Balancer

This page shows how to create an External Load Balancer.

Note: This feature is only available for cloud providers or environments which support external load balancers.

When creating a service, you have the option of automatically creating a cloud network load balancer. This provides an externally-accessible IP address that sends traffic to the correct port on your cluster nodes provided your cluster runs in a supported environment and is configured with the correct cloud load balancer provider package.

For information on provisioning and using an Ingress resource that can give services externally-reachable URLs, load balance the traffic, terminate SSL etc., please check the Ingress documentation.

Before you begin

  • You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

    To check the version, enter kubectl version.

Configuration file

To create an external load balancer, add the following line to your service configuration file:

  1.     type: LoadBalancer

Your configuration file might look like:

  1. apiVersion: v1
  2. kind: Service
  3. metadata:
  4.   name: example-service
  5. spec:
  6.   selector:
  7.     app: example
  8.   ports:
  9.     - port: 8765
  10.       targetPort: 9376
  11.   type: LoadBalancer

Using kubectl

You can alternatively create the service with the kubectl expose command and its --type=LoadBalancer flag:

  1. kubectl expose rc example --port=8765 --target-port=9376 \
  2.         --name=example-service --type=LoadBalancer

This command creates a new service using the same selectors as the referenced resource (in the case of the example above, a replication controller named example).

For more information, including optional flags, refer to the kubectl expose reference.

Finding your IP address

You can find the IP address created for your service by getting the service information through kubectl:

  1. kubectl describe services example-service

which should produce output like this:

  1.     Name:                   example-service
  2.     Namespace:              default
  3.     Labels:                 <none>
  4.     Annotations:            <none>
  5.     Selector:               app=example
  6.     Type:                   LoadBalancer
  7.     IP:                     10.67.252.103
  8.     LoadBalancer Ingress:   192.0.2.89
  9.     Port:                   <unnamed> 80/TCP
  10.     NodePort:               <unnamed> 32445/TCP
  11.     Endpoints:              10.64.0.4:80,10.64.1.5:80,10.64.2.4:80
  12.     Session Affinity:       None
  13.     Events:                 <none>

The IP address is listed next to LoadBalancer Ingress.

Note: If you are running your service on Minikube, you can find the assigned IP address and port with:

  1. minikube service example-service --url

Preserving the client source IP

Due to the implementation of this feature, the source IP seen in the target container is not the original source IP of the client. To enable preservation of the client IP, the following fields can be configured in the service spec (supported in GCE/Google Kubernetes Engine environments):

  • service.spec.externalTrafficPolicy - denotes if this Service desires to route external traffic to node-local or cluster-wide endpoints. There are two available options: Cluster (default) and Local. Cluster obscures the client source IP and may cause a second hop to another node, but should have good overall load-spreading. Local preserves the client source IP and avoids a second hop for LoadBalancer and NodePort type services, but risks potentially imbalanced traffic spreading.
  • service.spec.healthCheckNodePort - specifies the health check node port (numeric port number) for the service. If healthCheckNodePort isn’t specified, the service controller allocates a port from your cluster’s NodePort range. You can configure that range by setting an API server command line option, --service-node-port-range. It will use the user-specified healthCheckNodePort value if specified by the client. It only has an effect when type is set to LoadBalancer and externalTrafficPolicy is set to Local.

Setting externalTrafficPolicy to Local in the Service configuration file activates this feature.

  1. apiVersion: v1
  2. kind: Service
  3. metadata:
  4.   name: example-service
  5. spec:
  6.   selector:
  7.     app: example
  8.   ports:
  9.     - port: 8765
  10.       targetPort: 9376
  11.   externalTrafficPolicy: Local
  12.   type: LoadBalancer

Garbage Collecting Load Balancers

FEATURE STATE: Kubernetes v1.17 [stable]

In usual case, the correlating load balancer resources in cloud provider should be cleaned up soon after a LoadBalancer type Service is deleted. But it is known that there are various corner cases where cloud resources are orphaned after the associated Service is deleted. Finalizer Protection for Service LoadBalancers was introduced to prevent this from happening. By using finalizers, a Service resource will never be deleted until the correlating load balancer resources are also deleted.

Specifically, if a Service has type LoadBalancer, the service controller will attach a finalizer named service.kubernetes.io/load-balancer-cleanup. The finalizer will only be removed after the load balancer resource is cleaned up. This prevents dangling load balancer resources even in corner cases such as the service controller crashing.

External Load Balancer Providers

It is important to note that the datapath for this functionality is provided by a load balancer external to the Kubernetes cluster.

When the Service type is set to LoadBalancer, Kubernetes provides functionality equivalent to type equals ClusterIP to pods within the cluster and extends it by programming the (external to Kubernetes) load balancer with entries for the Kubernetes pods. The Kubernetes service controller automates the creation of the external load balancer, health checks (if needed), firewall rules (if needed) and retrieves the external IP allocated by the cloud provider and populates it in the service object.

Caveats and Limitations when preserving source IPs

GCE/AWS load balancers do not provide weights for their target pools. This was not an issue with the old LB kube-proxy rules which would correctly balance across all endpoints.

With the new functionality, the external traffic is not equally load balanced across pods, but rather equally balanced at the node level (because GCE/AWS and other external LB implementations do not have the ability for specifying the weight per node, they balance equally across all target nodes, disregarding the number of pods on each node).

We can, however, state that for NumServicePods << NumNodes or NumServicePods >> NumNodes, a fairly close-to-equal distribution will be seen, even without weights.

Once the external load balancers provide weights, this functionality can be added to the LB programming path. Future Work: No support for weights is provided for the 1.4 release, but may be added at a future date

Internal pod to pod traffic should behave similar to ClusterIP services, with equal probability across all pods.