Getting Started with Load Balancing on a Linode Kubernetes Engine (LKE) Cluster

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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:

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:

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.
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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

Annotation (suffix)ValuesDefault ValueDescription
throttle• integer
0-20
0 disables the throttle
20The client connection throttle limits the number of new connections-per-second from the same client IP.
default-protocol• string
tcp, http, https
tcpSpecifies the protocol for the NodeBalancer to use.
proxy-protocol• string
none, v1, v2
noneEnables Proxy Protocol on the underlying NodeBalancer and specifies the version of Proxy Protocol to use. The Proxy Protocol allows TCP client connection information, like IP address and port number, to be transferred to cluster nodes. See the Using Proxy Protocol with NodeBalancers guide for details on each Proxy Protocol version.
port-*A JSON object of port configurations
For example:
{ "tls-secret-name": "prod-app-tls", "protocol": "https"})
None• Specifies a NodeBalancer port to configure, i.e. port-443.

• Ports 1-65534 are available for balancing.

• The available port configurations are:

"tls-secret-name" use this key to provide a Kubernetes secret name when setting up TLS termination for a service to be accessed over HTTPS. The secret type should be kubernetes.io/tls.

"protocol" specifies the protocol to use for this port, i.e. tcp, http, https. The default protocol is tcp, unless you provided a different configuration for the default-protocol annotation.
check-type• string
none, connection, http, http_body
None• The type of health check to perform on Nodes to ensure that they are serving requests. The behavior for each check is the following:

none no check is performed

connection checks for a valid TCP handshake

http checks for a 2xx or 3xx response code

http_body checks for a specific string within the response body of the healthcheck URL. Use the check-body annotation to provide the string to use for the check.
check-pathstringNoneThe URL path that the NodeBalancer will use to check on the health of the back-end Nodes.
check-bodystringNoneThe string that must be present in the response body of the URL path used for health checks. You must have a check-type annotation configured for a http_body check.
check-intervalintegerNoneThe duration, in seconds, between health checks.
check-timeout• integer
• value between 1-30
NoneDuration, in seconds, to wait for a health check to succeed before it is considered a failure.
check-attempts• integer
• value between 1-30
NoneNumber of health checks to perform before removing a back-end Node from service.
check-passiveBooleanfalseWhen true, 5xx status codes will cause the health check to fail.
preserveBooleanfalseWhen true, deleting a LoadBalancer service does not delete the underlying NodeBalancer
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-serivce.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-serivce.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.

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