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
- Configuration file
- Using kubectl
- Finding your IP address
- Preserving the client source IP
- Garbage Collecting Load Balancers
- External Load Balancer Providers
- Caveats and Limitations when preserving source IPs
Before you begin
You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. 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
To create an external load balancer, add the following line to your service configuration file:
Your configuration file might look like:
apiVersion: v1 kind: Service metadata: name: example-service spec: selector: app: example ports: - port: 8765 targetPort: 9376 type: LoadBalancer
You can alternatively create the service with the
kubectl expose command and
kubectl expose rc example --port=8765 --target-port=9376 \ --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
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
kubectl describe services example-service
which should produce output like this:
Name: example-service Namespace: default Labels: <none> Annotations: <none> Selector: app=example Type: LoadBalancer IP: 10.67.252.103 LoadBalancer Ingress: 192.0.2.89 Port: <unnamed> 80/TCP NodePort: <unnamed> 32445/TCP Endpoints: 10.64.0.4:80,10.64.1.5:80,10.64.2.4:80 Session Affinity: None Events: <none>
The IP address is listed next to
Note: If you are running your service on Minikube, you can find the assigned IP address and port with:
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 nodePort (numeric port number) for the service. If not specified,
healthCheckNodePortis created by the service API backend with the allocated
nodePort. It will use the user-specified
nodePortvalue if specified by the client. It only has an effect when
typeis set to LoadBalancer and
externalTrafficPolicyis set to Local.
externalTrafficPolicy to Local in the Service configuration file
activates this feature.
apiVersion: v1 kind: Service metadata: name: example-service spec: selector: app: example ports: - port: 8765 targetPort: 9376 externalTrafficPolicy: Local type: LoadBalancer
Garbage Collecting Load Balancers
- The version name is vX where X is an integer.
- Stable versions of features will appear in released software for many subsequent versions.
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
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
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.
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