Getting Started with Load Balancing on an LKE Cluster

The Linode Kubernetes Engine (LKE) is Linode’s managed Kubernetes service. When you deploy an LKE cluster, you receive a Kubernetes Master which runs your cluster’s control plane components, at no additional cost. The control plane includes Linode’s Cloud Controller Manager (CCM), which provides a way for your cluster to access additional Linode services. Linode’s CCM provides access to Linode’s load balancing service, Linode NodeBalancers.

NodeBalancers provide your Kubernetes cluster with a reliable way of exposing resources to the public internet. The LKE control plane handles the creation and deletion of the NodeBalancer, and correctly identifies the resources, and their networking, that the NodeBalancer will route traffic to. Whenever a Kubernetes Service of the LoadBalancer type is created, your Kubernetes cluster will create a Linode NodeBalancer service with the help of the Linode CCM.

Note

Adding external Linode NodeBalancers to your LKE cluster will incur additional costs. See Linode’s Pricing page for details.

Note

All existing LKE clusters receive CCM updates automatically every two weeks when a new LKE release is deployed. See the LKE Changelog for information on the latest LKE release.

Note

The Linode Terraform K8s module also deploys a Kubernetes cluster with the Linode CCM installed by default. Any Kubernetes cluster with a Linode CCM installation can make use of Linode NodeBalancers in the ways described in this guide.

In this Guide

This guide will show you:

• manifest file configurations needed to add Linode NodeBalancers to your LKE cluster.
• annotations available to further configure your Linode NodeBalancers behavior and how to incorporate them into a manifest file.
• prerequisites and annotations needed to configure TLS termination on your cluster’s NodeBalancers.
• how to configure session affinity for the Pods in a cluster.

Before You Begin

This guide assumes you have a working Kubernetes cluster that was deployed using the Linode Kubernetes Engine (LKE). You can deploy a Kubernetes cluster using LKE in the following ways:

• The Linode Cloud Manager.

• Linode’s API v4.

• Terraform, the popular infrastructure as code (IaC) tool.

  Note

  An LKE cluster will already have Linode’s Cloud Controller Manager installed in the cluster’s control plane. If you did not deploy your Kubernetes cluster using LKE and would like to make use of the Linode Cloud Controller Manager, see Installing the Linode CCM on an Unmanaged Kubernetes Cluster - A Tutorial.

Adding Linode NodeBalancers to your Kubernetes Cluster

To add an external load balancer to your Kubernetes cluster you can add the example lines to a new configuration file, or more commonly, to a Service file. When the configuration is applied to your cluster, Linode NodeBalancers will be created, and added to your Kubernetes cluster. Your cluster will be accessible via a public IP address and the NodeBalancers will route external traffic to a Service running on healthy nodes in your cluster.

Note

Billing for Linode NodeBalancers begin as soon as the example configuration is successfully applied to your Kubernetes cluster.

In any NodeBalancer configuration, users should keep in mind that NodeBalancers have a maximum connection limit of 10,000 concurrent connections.

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spec: type: LoadBalancer ports: - name: http port: 80 protocol: TCP targetPort: 80

• The spec.type of LoadBalancer is responsible for telling Kubernetes to create a Linode NodeBalancer.
• The remaining lines provide port definitions for your Service’s Pods and maps an incoming port to a container’s targetPort.

Viewing Linode NodeBalancer Details

To view details about running NodeBalancers on your cluster:

1. Get the services running on your cluster:

    kubectl get services
   

   You will see a similar output:

   NAME            TYPE           CLUSTER-IP      EXTERNAL-IP    PORT(S)        AGE
   kubernetes      ClusterIP      10.128.0.1      none           443/TCP        3h5m
   example-service LoadBalancer   10.128.171.88   45.79.246.55   80:30028/TCP   36m

   • Viewing the entry for the example-service, you can find your NodeBalancer’s public IP under the EXTERNAL-IP column.
   • The PORT(S) column displays the example-service incoming port and NodePort.

2. View details about the example-service to retrieve information about the deployed NodeBalancers:

    kubectl describe service example-service
   

   Name:                     nginx-service
   Namespace:                default
   Labels:                   app=nginx
   Annotations:              service.beta.kubernetes.io/linode-loadbalancer-throttle: 4
   Selector:                 app=nginx
   Type:                     LoadBalancer
   IP:                       10.128.171.88
   LoadBalancer Ingress:     192.0.2.0
   Port:                     http  80/TCP
   TargetPort:               80/TCP
   NodePort:                 http  30028/TCP
   Endpoints:                10.2.1.2:80,10.2.1.3:80,10.2.2.2:80
   Session Affinity:         None
   External Traffic Policy:  Cluster
   Events:                   <none>

Configuring your Linode NodeBalancers with Annotations

The Linode CCM accepts annotations that configure the behavior and settings of your cluster’s underlying NodeBalancers.

• The table below provides a list of all available annotation suffixes.
• Each annotation must be prefixed with service.beta.kubernetes.io/linode-loadbalancer-. For example, the complete value for the throttle annotation is service.beta.kubernetes.io/linode-loadbalancer-throttle.
• Annotation values such as http are case-sensitive.

Annotations Reference

Note

To view a list of deprecated annotations, visit the Linode CCM GitHub repository.

Configuring Linode NodeBalancers for TLS Encryption

This section describes how to set up TLS termination on your Linode NodeBalancers so a Kubernetes Service can be accessed over HTTPS.

Generating a TLS type Secret

Kubernetes allows you to store sensitive information in a Secret object for use within your cluster. This is useful for storing things like passwords and API tokens. In this section, you will create a Kubernetes secret to store Transport Layer Security (TLS) certificates and keys that you will then use to configure TLS termination on your Linode NodeBalancers.

In the context of the Linode CCM, Secrets are useful for storing Transport Layer Security (TLS) certificates and keys. The linode-loadbalancer-tls annotation requires TLS certificates and keys to be stored as Kubernetes Secrets with the type tls. Follow the steps in this section to create a Kubernetes TLS Secret.

Note

The steps in this section will create a self-signed TLS certificate. To learn how to create a TLS certificate from the Let’s Encrypt certificate authority (CA) and apply it to an application running on Kubernetes, see the Configuring Load Balancing with TLS Encryption on a Kubernetes Cluster.

1. Generate a TLS key and certificate using a TLS toolkit like OpenSSL. Be sure to change the CN and O values to those of your own website domain.

   openssl req -newkey rsa:4096 \
       -x509 \
       -sha256 \
       -days 3650 \
       -nodes \
       -out tls.crt \
       -keyout tls.key \
       -subj "/CN=mywebsite.com/O=mywebsite.com"
   

2. Create the secret using the create secret tls command. Ensure you substitute $SECRET_NAME for the name you’d like to give to your secret. This will be how you reference the secret in your Service manifest.

   kubectl create secret tls $SECRET_NAME --cert tls.crt --key tls.key
   

3. You can check to make sure your Secret has been successfully stored by using describe:

   kubectl describe secret $SECRET_NAME
   

   You should see output like the following:

   kubectl describe secret docteamdemosite
   Name:         my-secret
   Namespace:    default
   Labels:       <none>
   Annotations:  <none>
   
   Type:  kubernetes.io/tls
   
   Data
   ====
   tls.crt:  1164 bytes
   tls.key:  1704 bytes

   If your key is not formatted correctly you’ll receive an error stating that there is no PEM formatted data within the key file.

Configuring TLS within a Service

By default, Kubernetes does not expose Services with TLS termination over HTTPS. In order to use https you’ll need to instruct the Service to use the correct port using the required annotations. You can add the following code snippet to a Service file to enable TLS termination on your NodeBalancers:

File: example-service.yaml

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... metadata: annotations: service.beta.kubernetes.io/linode-loadbalancer-default-protocol: http service.beta.kubernetes.io/linode-loadbalancer-port-443: '{ "tls-secret-name": "example-secret", "protocol": "https" }' ...

• The service.beta.kubernetes.io/linode-loadbalancer-default-protocol annotation configures the NodeBalancer’s default protocol.

• service.beta.kubernetes.io/linode-loadbalancer-port-443 specifies port 443 as the port to be configured. The value of this annotation is a JSON object designating the TLS secret name to use (example-secret) and the protocol to use for the port being configured (https).

If you have multiple Secrets and ports for different environments (testing, staging, etc.), you can define more than one secret and port pair:

File: example-service.yaml

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... metadata: annotations: service.beta.kubernetes.io/linode-loadbalancer-default-protocol: http service.beta.kubernetes.io/linode-loadbalancer-port-443: '{ "tls-secret-name": "example-secret", "protocol": "https" }' service.beta.kubernetes.io/linode-loadbalancer-port-8443: '{ "tls-secret-name": "example-secret-staging", "protocol": "https" }' ...

Configuring Session Affinity for Cluster Pods

kube-proxy will always attempt to proxy traffic to a random backend Pod. To direct traffic to the same Pod, you can use the sessionAffinity mechanism. When set to clientIP, sessionAffinity will ensure that all traffic from the same IP will be directed to the same Pod. You can add the example lines to a Service configuration file to

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spec: type: LoadBalancer selector: app: example-app sessionAffinity: ClientIP sessionAffinityConfig: clientIP: timeoutSeconds: 100

Removing Linode NodeBalancers from your Kubernetes Cluster

To delete a NodeBalancer and the Service that it represents, you can use the Service manifest file you used to create the NodeBalancer. Simply use the delete command and supply your file name with the f flag:

kubectl delete -f example-service.yaml

Similarly, you can delete the Service by name:

kubectl delete service example-service

After deleting your service, its corresponding NodeBalancer will be removed from your Linode account.

Note

If your Service file used the preserve annotation, the underlying NodeBalancer will not be removed from your Linode account. See the annotations reference for details.