Create an External Load Balancer
This page shows how to create an external load balancer.
When creating a Service, you have the option of automatically creating a cloud 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.
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:
Your cluster must be running in a cloud or other environment that already has support for configuring external load balancers.
Create a Service
Create a Service from a manifest
To create an external load balancer, add the following line to your Service manifest:
Your manifest might then look like:
apiVersion: v1 kind: Service metadata: name: example-service spec: selector: app: example ports: - port: 8765 targetPort: 9376 type: LoadBalancer
Create a Service using kubectl
You can alternatively create the service with the
kubectl expose command and
kubectl expose deployment 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
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 similar to:
Name: example-service Namespace: default Labels: app=example Annotations: <none> Selector: app=example Type: LoadBalancer IP Families: <none> IP: 10.3.22.96 IPs: 10.3.22.96 LoadBalancer Ingress: 192.0.2.89 Port: <unset> 8765/TCP TargetPort: 9376/TCP NodePort: <unset> 30593/TCP Endpoints: 172.17.0.3:9376 Session Affinity: None External Traffic Policy: Cluster Events: <none>
The load balancer's IP address is listed next to
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
By default, 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
.spec of the Service:
.spec.externalTrafficPolicy- denotes if this Service desires to route external traffic to node-local or cluster-wide endpoints. There are two available options:
Clusterobscures the client source IP and may cause a second hop to another node, but should have good overall load-spreading.
Localpreserves the client source IP and avoids a second hop for LoadBalancer and NodePort type Services, but risks potentially imbalanced traffic spreading.
.spec.healthCheckNodePort- specifies the health check node port (numeric port number) for the service. If you don't specify
healthCheckNodePort, 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. The Service will use the user-specified
healthCheckNodePortvalue if you specify it, provided that the Service
typeis set to LoadBalancer and
externalTrafficPolicyis set to
externalTrafficPolicy to Local in the Service manifest
activates this feature. For example:
apiVersion: v1 kind: Service metadata: name: example-service spec: selector: app: example ports: - port: 8765 targetPort: 9376 externalTrafficPolicy: Local type: LoadBalancer
Caveats and limitations when preserving source IPs
Load balancing services from some cloud providers do not let you configure different weights for each target.
With each target weighted equally in terms of sending traffic to Nodes, external traffic is not equally load balanced across different Pods. The external load balancer is unaware of the number of Pods on each node that are used as a target.
NumServicePods << _NumNodes or
NumServicePods >> NumNodes, a fairly close-to-equal
distribution will be seen, even without weights.
Internal pod to pod traffic should behave similar to ClusterIP services, with equal probability across all pods.
Garbage collecting load balancers
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
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 nodes
hosting the relevant Kubernetes pods. The Kubernetes control plane automates the creation of the external load balancer,
health checks (if needed), and packet filtering rules (if needed). Once the cloud provider allocates an IP address for the load
balancer, the control plane looks up that external IP address and populates it into the Service object.