Expose your app deployed on an OVHcloud Managed Kubernetes Service

Objective

In this tutorial we are explaining how to use services on OVHcloud Managed Kubernetes service to expose your app by getting external traffic into your cluster. We will begin by listing the main methods to expose Kubernetes services outside the cluster, with their advantages and disadvantages. Then we will see a complete example of LoadBalancer service deployment.

Before you begin

This tutorial presupposes that you already have a working OVHcloud Managed Kubernetes cluster and some basic knowledge of how to operate it. If you want to know more on those topics, please look at the OVHcloud Managed Kubernetes Service Quickstart.

Some concepts: ClusterIP, NodePort, Ingress and LoadBalancer

When you begin to use Kubernetes for real applications, one of the first questions is how to get external traffic into your cluster. The official doc gives you a good but rather dry explanation of the topic, but here we are trying to explain the concepts in a minimal, need-to-know way.

There are several ways to route the external traffic into your cluster:

• Using Kubernetes proxy and ClusterIP: The default Kubernetes ServiceType is ClusterIP, which exposes the Service on a cluster-internal IP. To reach the ClusterIP from an external source, you can open a Kubernetes proxy between the external source and the cluster. It is usually only used for development.

• Exposing services as NodePort: Declaring a Service of type NodePort exposes the service on each Node’s IP at a static port (the NodePort). You can then access the Service from the outside of the cluster by requesting <NodeIp>:<NodePort>. It can be used for production, with some limitations.

• Exposing services as LoadBalancer: Declaring a Service of type LoadBalancer exposes it externally using a cloud provider’s load balancer. The cloud provider will provision a load balancer for the Service, and map it to its automatically assigned NodePort. It is the most widely used method in production environments.

Using Kubernetes proxy and ClusterIP

The default Kubernetes ServiceType is ClusterIP, which exposes the Service on a cluster-internal IP. To reach the ClusterIP from an external computer, you can open a Kubernetes proxy between the external computer and the cluster.

You can use kubectl to create such a proxy. When the proxy is up, you're directly connected to the cluster, and you can use the Services internal IP (ClusterIP).

This method isn't suited for a production environment, but it's interesting for development, debugging or other quick-and-dirty operations.

Exposing services as NodePort

Declaring a service of type NodePort exposes the Service on each Node’s IP at a static port, the NodePort (a fixed port for that Service, in the default range of 30000-32767). You can then access the Service from the outside of the cluster by requesting <NodeIp>:<NodePort>. Every service you deploy as NodePort will be exposed in its own port, on every Node.

It's rather cumbersome to use NodePort Services in production. As you are using non-standard ports, you often need to set up an external load balancer that listens on standard ports and redirects the traffic to the <NodeIp>:<NodePort>.

$ kubectl cluster-info
Kubernetes control plane is running at https://xxxxxx.c1.gra9.k8s.ovh.net
CoreDNS is running at https://xxxxxxx.c1.gra9.k8s.ovh.net/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
Metrics-server is running at https://xxxxxx.c1.gra9.k8s.ovh.net/api/v1/namespaces/kube-system/services/https:metrics-server:/proxy

Exposing services as LoadBalancer

Declaring a service of type LoadBalancer exposes it externally using a cloud provider’s load balancer. The cloud provider will provision a load balancer for the Service, and map it to its automatically assigned NodePort. How the traffic from that external load balancer is routed to the Service pods depends on the cluster provider.

The LoadBalancer is the best option for a production environment, with two caveats:

• Every Service of type LoadBalancer you deploy will get its own IP.
• The LoadBalancer is usually billed by the number of exposed services, it can be expensive.

Supported Load Balancers

OVHcloud currently provides two types of load balancers that can be used with Managed Kubernetes Services:

• Load Balancer for Managed Kubernetes, this load balancer type can only be used to expose resources of a Managed Kubernetes Service. It supports up to 2000 requests/second and a 200Mbits/s bandwidth. Please note that this Loadbalancer will be depracated from MKS Kubernetes version 1.32 and upwards.
• Public Load Balancer, based on the OpenStack Octavia project, this load balancer type can also be used with standard OVHcloud instances. You can choose between three Load Balancer sizes (S,M,L), providing up to 40k requests/second and a 2 Gbits/second bandwidth. Other advantages are the capability to expose your Load Balancer privately (private-to-private) or publicly (public-to-private or public-to-public) using Floating IPs, the possibility to collect metrics and TCP/UDP protocols.

Supported annotations

There are several annotations available to customize your load balancer:

• service.beta.kubernetes.io/ovh-loadbalancer-proxy-protocol: Used on the service to enable the proxy protocol on all backends. Supported values: v1, v2, v2_ssl, v2_ssl_cn.

OVHcloud Load Balancer services handle 4 ProxyProtocol modes:

• service.beta.kubernetes.io/ovh-loadbalancer-allowed-sources: Used on the service to specify allowed client IP source ranges. Value: comma separated list of CIDRs. For example: 10.0.0.0/24,172.10.0.1. Deprecated, please use loadBalancerSourceRanges spec instead, see Restrict Access For LoadBalancer Service.

• service.beta.kubernetes.io/ovh-loadbalancer-balance: Used on the service to set the algorithm to use for load balancing. Supported values: first, leastconn, roundrobin, source. Default: roundrobin.

What about Ingress

According to the official documentation, an Ingress is an API object that manages external access to the services in a cluster, typically HTTP. What is the difference with the LoadBalancer or NodePort?

Ingress isn't a type of Service, but an object that acts as a reverse proxy, and single entrypoint to your cluster that routes the request to the different services. The most basic Ingress is the NGINX Ingress Controller, where the NGINX take the role of reverse proxy, but also functions as SSL.

An Ingress is exposed to the outside of the cluster either via ClusterIP and Kubernetes proxy, NodePort or LoadBalancer, and it routes incoming traffic according to configured rules.

The main advantage of using an Ingress behind a LoadBalancer is the cost: you can have lots of services behind a single LoadBalancer.

Deploying LoadBalancer Services on OVHcloud Managed Kubernetes clusters

In our OVHcloud Managed Kubernetes we propose a load balancing service enabling you to use LoadBalancer ServiceType.

Deploying a Hello World LoadBalancer service

Create a hello.yml file for our ovhplatform/hello Docker image, defining the service type as LoadBalancer:

apiVersion: v1
kind: Service
metadata:
  name: hello-world
  labels:
    app: hello-world
spec:
  type: LoadBalancer
  ports:
  - port: 80
    targetPort: 80
    protocol: TCP
    name: http
  selector:
    app: hello-world
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: hello-world-deployment
  labels:
    app: hello-world
spec:
  replicas: 1
  selector:
    matchLabels:
      app: hello-world
  template:
    metadata:
      labels:
        app: hello-world
    spec:
      containers:
      - name: hello-world
        image: ovhplatform/hello:1.1
        ports:
        - containerPort: 80

And apply the file:

kubectl apply -f hello.yml

After applying the YAML file, a new hello-world service and the corresponding hello-world-deployment deployment are created:

$ kubectl apply -f hello.yml

service/hello-world unchanged
deployment.apps/hello-world-deployment configured

List the services

And now you're going to use kubectl to see your service:

kubectl get service hello-world -w

You should see your newly created service:

$ kubectl get services
NAME          TYPE           CLUSTER-IP    EXTERNAL-IP     PORT(S)            AGE
hello-world   LoadBalancer   10.3.81.234   <pending>       80:31699/TCP       9s

As the LoadBalancer creation is asynchronous, and the provisioning of the load balancer can take several minutes, you will surely get a <pending> EXTERNAL-IP.

If you try again in a few minutes you should get an EXTERNAL-IP:

$ kubectl get service hello-world
NAME          TYPE           CLUSTER-IP    EXTERNAL-IP       PORT(S)        AGE
hello-world   LoadBalancer   10.3.81.234   xxx.xxx.xxx.xxx   80:31699/TCP   4m

For each service you deploy with LoadBalancer type, you will get a new IPv4 with the xxx.xxx.xxx.xxx format to access the service.

Testing your service

If you point your web browser to the EXTERNAL-IP value, the hello-world service will answer you:

Cleaning up

At the end you can proceed to clean up by deleting the service and the deployment.

Let's begin by deleting the service:

kubectl delete service hello-world

If you list the services you will see that hello-world doesn't exist anymore:

$ kubectl delete service hello-world
service "hello-world" deleted

$ kubectl get services -l app=hello-world
No resources found.

Then, you can delete the deployment:

kubectl delete deploy hello-world-deployment

And now if you list your deployment you will find no resource:

$ kubectl delete deploy hello-world-deployment
deployment.apps "hello-world-deployment" deleted

$ kubectl get deployments -l app=hello-world
No resources found.

If now you list the pods:

kubectl get pod -n default -l app=hello-world

You will see that the pod created for hello-world has been deleted too:

$ kubectl get pod -l app=hello-world
No resources found

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