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Step-by-step instructions for performing operations with Kubernetes.

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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 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.

Before you begin

Configuration file

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

    "type": "LoadBalancer"

Your configuration file might look like:

    {
      "kind": "Service",
      "apiVersion": "v1",
      "metadata": {
        "name": "example-service"
      },
      "spec": {
        "ports": [{
          "port": 8765,
          "targetPort": 9376
        }],
        "selector": {
          "app": "example"
        },
        "type": "LoadBalancer"
      }
    }

Using kubectl

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

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 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:

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:   123.45.678.9
    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 LoadBalancer Ingress.

Preserving the client source IP

Due to the implementation of this feature, the source IP seen in the target container will not be 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/GKE environments):

This feature can be activated by setting externalTrafficPolicy to “Local” in the Service Configuration file.

    {
      "kind": "Service",
      "apiVersion": "v1",
      "metadata": {
        "name": "example-service"
      },
      "spec": {
        "ports": [{
          "port": 8765,
          "targetPort": 9376
        }],
        "selector": {
          "app": "example"
        },
        "type": "LoadBalancer",
        "externalTrafficPolicy": "Local"
      }
    }

Feature availability

k8s version Feature support
1.7+ Supports the full API fields
1.5 - 1.6 Supports Beta Annotations
<1.5 Unsupported

Below you could find the deprecated Beta annotations used to enable this feature prior to its stable version. Newer Kubernetes versions may stop supporting these after v1.7. Please update existing applications to use the fields directly.

service.beta.kubernetes.io/external-traffic annotation has a different set of values compared to the service.spec.externalTrafficPolicy field. The values match as follows:

Note that this feature is not currently implemented for all cloudproviders/environments.

Known issues:

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=<ClusterIP> to pods within the cluster and extends it by programming the (external to Kubernetes) load balancer with entries for the Kubernetes VMs. 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 will not be 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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