Let's now add an important element to our cluster, in order to get closer and closer to creating an HA cluster.

What is Ingress?

In Kubernetes, an Ingress is a object that allows access to your Kubernetes services from outside the cluster. The ingress is made up of 2 parts: the kubernetes component that deals with directing external traffic to internal services is called the ingress controller, which obeys the rules present in the ingress resources. So, you configure access by creating a collection of rules, written in a file, that define which inbound connections reach which services. Without the use of the ingress, all the cluster services, to which one wishes to access from the outside, must be exposed to the internet. The advantage of the ingress consists, in fact, in exposing a single access point externally, which will take care of routing the traffic within the cluster.

Ingress installation

Prerequisites

First we added assign a new node label to the a cluster node, which will take care of routing incoming requests to the appropriate services. This node will receive requests from the internet, so it must have a FIP.So, we created a new VM (Launch and manage instances) with a low-medium flavor, as it should only act as an ingress, and joined it to cluster, using the comand kubeadm join (Building the cluster). We then assigned to the node, through a label, the "role" of ingress with the command

# Enter the node name and label. The optional "--overwrite" flag is used in case the value is already present
$ kubectl label node <node_name> kubernetes.io/role=<label_value> [--overwrite]
# Alternatively, you can edit the label directly in a text editor
$ kubectl edit node <node_name>

The addition of the label will be used later, to indicate on which node to install the input controller Pod. The same operation can also be performed on the other nodes (, assigning the role of worker), in order to obtain

# Note the "ROLES" column
$ kubectl get node
NAME                     STATUS   ROLES     AGE     VERSION
mycentos-0.novalocal     Ready    master    70d     v1.20.05
mycentos-1.novalocal     Ready    worker    69d     v1.20.05
mycentos-2.novalocal     Ready    worker    69d     v1.20.05
mycentos-ing3.novalocal     Ready    ingress   4d19h   v1.20.05

Ingress Controller

As said previously, you must have an Ingress controller to satisfy an Ingress. Only creating an Ingress resource has no effect. There are several input controllers, here we will use one of the most used. We will use the Nginx Ingress Controller guide as a reference. For more information, we recommend that you consult the official guide (an installation with Heml is Helm is also available on the same site).

...

$ git clone https://github.com/nginxinc/kubernetes-ingress/
$ cd kubernetes-ingress/deployments
$ git checkout v1.811.13

Before continuing, let's stop for a moment, because we need to make some small changes to the files in the folder we just cloned from the GitHub repo. The files in question are located here:

...

args:
  - -nginx-configmaps=$(POD_NAMESPACE)/nginx-config
  - -default-server-tls-secret=$(POD_NAMESPACE)/default-server-secret
 # - -v=3 # Enables extensive logging. Useful for troubleshooting.
   - -report-ingress-status                                              #----- Uncommented
 # - -external-service=nginx-ingress
 #- -enable-prometheus-metrics
 #- -global-configuration=$(POD_NAMESPACE)/nginx-configuration
  - -enable-leader-election                                              #----- Uncommented
 #- -enable-custom-resources

...

# Note that the Pod is present on the "ingress" node and has its own private IP
$ kubectl get pod -n nginx-ingress -o wide
NAME                             READY   STATUS    RESTARTS   AGE   IP               NODE
nginx-ingress-68d7b4bfdd-mw479   1/1     Running   0          20h   192.168.100.13   mycentos-ing.novalocal

Ingress resource

We now present the ingress resource through a complete example, present in the directory downloaded from GitHub (/kubernetes-ingress/examples/complete-example). Let's move inside the complete-example directory and run the commands (we set aside the cafe-secret.yaml file for now)

$ ls
cafe-ingress.yaml  cafe-secret.yaml  cafe.yaml  dashboard.png  README.md
$ kubectl apply -f cafe.yaml -n nginx-ingress

At this point we check that the Pods and the associated services have been created

...

apiVersion: networking.k8s.io/v1beta1v1
kind: Ingress
metadata:
  name: cafe-ingress
spec:
#  tls:                             # Let's ignore 
#  - hosts:                         # and comment 
#    - cafe.example.com             # these lines 
#    secretName: cafe-secret        # for the moment
  rules:
  - host: cafe.example.com
    http:
      paths:
      - path: /tea                  # Use cafe.example.com/tea to target "tea" services
        backendpathType: Prefix
          serviceNamebackend:
          service:
            name: tea-svc      # Enter the service name
          servicePort  port: 80
              number: 80       # Enter the port number on which the service is listening
      - path: /coffee               # Use cafe.example.com/coffee to target "coffee" services
        pathType: Prefix
        backend:
          service:
      serviceName      name: coffee-svc   # Enter the service name
            servicePort: 80port:
              number: 80	   # Enter the port number on which the service is listening

...

# In the ADDRESS column there is the FIP of the ingress node
$ kubectl get ing -n nginx-ingress
NAME                           CLASS    HOSTS              ADDRESS          PORTS     AGE
cafe-ingress                   <none>   cafe.example.com   131.154.97.164   80, 443   20h

Let's move to the browser

We prove that everything works by moving to the browser. Since the cafe.example.com site is not registered on a DNS, we have to insert a line in the /etc/hosts file of our local machine (example on Windows the full path is C:\Windows\System32\drivers\etc\hosts)

131.154.97.164 cafe.example.com # Insert FIP of the node and the host

...

These two web pages, while very simple, assure us that the addressing mechanism works correctly. Of course, if you don't enter any path (/tea or /coffee) after the host, you will get the message "404 Not Found". This happens because we have not associated any service in our ingress resource in the "homepage" of the host (i.e. the "- path: /" is not configured).

Uninstall the Ingress Controller

All the components created in this guide share the nginx-ingress namespace, so if we want to remove everything in one go, just type

...