1. Introduction to Ingress

Ingress is the mechanism in Kubernetes that is responsible for directing external requests to services within the cluster. By mapping services to URLs outside the cluster, external accessibility of services is achieved. Ingress supports configuring services in the cluster so that they can be accessed through external URLs, and also provides functions such as traffic load balancing and domain name-based virtual hosting.

A simple understanding of Ingress is to abstract the cumbersome steps that originally required manual modification of Nginx configuration and configuration of domain name and service mapping into an Ingress object. By using YAML files to create and update Ingress objects, we no longer need to manually operate Nginx configuration files, but manage the relationship between domain names and services in a more convenient way.

However, this raises a question: "How should Nginx handle these changes?" At this time, the Ingress Controller appears to specifically solve the problem of Nginx's processing method. The Ingress Controller interacts with the Kubernetes API and senses changes in Ingress rules in the cluster in real time. Once there are changes, the Ingress Controller will read these rules and generate the corresponding Nginx configuration based on its own template. Then, it writes this configuration to the Nginx Pod, and finally triggers the reload operation of Nginx to ensure that the configuration takes effect.

Through the cooperation of Ingress and Ingress Controller, we have become more flexible and convenient in managing external access. We have got rid of the trouble of manually modifying Nginx configuration, allowing us to focus more on the mapping relationship between services and domain names, and improving the maintainability of Kubernetes clusters. sex.

1.Ingress Controller Introduction

Ingress Controller is a seven-layer load balancing scheduler that serves as the first stop for client requests, receiving and processing all external requests. Under the action of this seven-layer load balancing scheduler, the request will pass through the reverse proxy and finally be routed to the backend Pod. Common seven-layer load balancers include nginx, traefik, etc. Taking the familiar nginx as an example, when a request reaches nginx, nginx will configure a reverse proxy to the backend Pod application through upstream.

Ingress Controller

However, the IP address of the backend Pod changes dynamically. To solve this problem, we introduced Service. This Service is not an actual service, but serves to group the backend Pods. Therefore, when configuring upstream, we only need to fill in the address of the Service and do not need to care about the specific IP address of the backend Pod.

Through this design, the Ingress Controller can flexibly handle changes in the backend Pod and ensure that requests can be correctly routed to services in the cluster. This model makes it easier for us to manage changes in backend services without having to worry about the problems caused by the constant changes in the Pod's IP address.

2.Ingress resources

A minimal Ingress resource example:

apiVersion:networking.k8s.io/v1
kind:Ingress
metadata:
  name:minimal-ingress
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target:/
spec:
  ingressClassName:nginx-example
  rules:
  -http:
      paths:
      -path:/testpath
        pathType:Prefix
        backend:
          service:
            name:test
            port:
              number:80
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Ingress needs to specify the apiVersion, kind, metadata and spec fields. The name of the Ingress object must be a legal DNS subdomain name[1].

3.Ingress Controller agent k8s internal application process

• Deploy the Ingress controller. Our ingress controller uses nginx.
• Create a Pod application, you can create a pod through the controller
• Create Service to group pods
• Create Ingress http and test accessing the application through http
• Create Ingress https and test accessing the application through https

You must have an ingress controller to meet the requirements of Ingress. Simply creating an Ingress resource is invalid.

Ingress

(1) Deploy ingress-nginx

Here we also use the killercoda platform for testing, which deploys the latest version V1.29.0 of the K8S environment.

Because Ingress is not deployed in this environment. The following is an example of deploying ingress-nginx[2]. By checking the official ingress-nginx, we know that V1.29.0 corresponds to V1.10.0 or v1.9.6 of Ingress-NGINX. as follows:

Ingress-NGINX version list

Deploy V1.10.0 of Ingress-NGINX by executing the following command.

kubectl apply -f \
https://raw.githubusercontent.com/kubernetes/ingress-nginx/controller-v1.10.0/deploy/static/provider/cloud/deploy.yaml
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After executing the above command, the following results will be output:

Check the deployment status through the following command:

controlplane $ kubectl get pod -n ingress-nginx
NAME                                        READY   STATUS      RESTARTS   AGE
ingress-nginx-admission-create-d69wp        0/1     Completed   0          102s
ingress-nginx-admission-patch-hkv66         0/1     Completed   0          102s
ingress-nginx-controller-7dcdbcff84-gfqcs   1/1     Running     0          102s
controlplane $ kubectl get svc  -n ingress-nginx
NAME                                 TYPE           CLUSTER-IP       EXTERNAL-IP   PORT(S)                      AGE
ingress-nginx-controller             LoadBalancer   10.98.23.38      <pending>     80:30770/TCP,443:31444/TCP   3m57s
ingress-nginx-controller-admission   ClusterIP      10.102.219.183   <none>        443/TCP                      3m57s
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(2) Deploy the backend tomcat service

Test the Ingress HTTP proxy k8s internal site by deploying the tomcat service and write the following resource list:

apiVersion:v1
kind:Service
metadata:
  name:tomcat
  namespace:default
spec:
  selector:
    app:tomcat
    release:canary
  ports:
    -name:scport
      targetPort:8080
      port:8009
---
apiVersion:apps/v1
kind:Deployment
metadata:
  name:tomcat-deploy
  namespace:default
spec:
  replicas:2
  selector:
    matchLabels:
      app:tomcat
      release:canary
  template:
    metadata:
      labels:
        app:tomcat
        release:canary
    spec:
      containers:
        -name:tomcat
          image:tomcat:8.5.34-jre8-alpine
          imagePullPolicy:IfNotPresent
          ports:
            -name:containerport
              containerPort:8080
              name:ajp
              containerPort:8009
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Check whether the pod is deployed successfully:

controlplane $ kubectl apply -f ingress-demo.yaml 
service/tomcat created
deployment.apps/tomcat-deploy created
controlplane $ kubectl get pod      
NAME                             READY   STATUS    RESTARTS   AGE
tomcat-deploy-7c67c4d459-5s859   1/1     Running   0          11m
tomcat-deploy-7c67c4d459-bvp2k   1/1     Running   0          11m
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(3) Write Ingress rules

apiVersion:networking.k8s.io/v1
kind:Ingress
metadata:
  name:ingress-myapp
  namespace:default
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target:/
spec:
  ingressClassName:nginx
  rules:# 定义后端的转发规则
   -host:tomcat.test.com# 通过域名进行转发
     http:
       paths:
         -path:/#配置访问路径，如果通过url进行转发。需要修改，空的默认访问路径是"/"
           pathType:Prefix
           backend:# 配置后端服务
             service:
               name:tomcat# 配置关联的serverce
               port:
                 number:8080# service暴露的端口
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ingressClassName: This value can be obtained through kubectl get ingressclasses.

View the details of ingress-myapp:

controlplane $ kubectl apply  -f ingress-myapp.yaml 
ingress.networking.k8s.io/ingress-myapp created
controlplane $ kubectl get ingress
NAME            CLASS   HOSTS             ADDRESS   PORTS   AGE
ingress-myapp   nginx   tomcat.test.com             80      8s
controlplane $ kubectl describe ingress ingress-myapp 
Name:             ingress-myapp
Labels:           <none>
Namespace:        default
Address:          
Ingress Class:    nginx
Default backend:  <default>
Rules:
  Host             Path  Backends
  ----             ----  --------
  tomcat.test.com  
                   /   tomcat:8080 ()
Annotations:       nginx.ingress.kubernetes.io/rewrite-target: /
Events:
  Type    Reason  Age   From                      Message
  ----    ------  ----  ----                      -------
  Normal  Sync    62s   nginx-ingress-controller  Scheduled for sync
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Check which node ingress-nginx is deployed on, as shown below:

From the above figure, we can see that ingress-nginx is deployed on node1, and the SVC method is deployed through LoadBalancer. If you want to access this backend tomcat service, you need to do domain name resolution. as follows:

...省略..
172.30.2.2 tomcat.test.com
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Normal access is as follows:

4.CKA real questions

(1) Screenshots of real questions

(2) Chinese analysis

Switch k8s cluster environment: kubectl config use-context k8s

Task:

Create a new nginx lngress resource as follows:

Name: pong Namespace: ing-internal

Expose service hi on path /hi using service port 5678

The availability of service hi can be checked using the following command, which should return hi, curl -kL/hi

(3) Official reference documents

Ingress[3]

(4) Solving problems and answering questions

Switch k8s cluster environment:

kubectl config use-context k8s
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Create a file called pong.yaml. The resource content is as follows:

apiVersion:networking.k8s.io/v1
kind:Ingress
metadata:
  name:pong
  namespace:ing-internal
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target:/
spec:
  ingressClassName:nginx-example
  rules:
  -http:
      paths:
      -path:/hi
        pathType:Prefix
        backend:
          service:
            name:hi
            port:
              number:5678
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• The value of ingressClassName is recommended to be passed kubectl get ingressclasses during the exam.
• The value of service.name is not told in the question. It is recommended to check it through kubectl get svc during the exam.

Submit resource list:

kubectl apply -f pong.yaml
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Verify with curl -kL<INTERNAL_IP>/hi to see if hi is returned.

References:

• [1]DNS subdomain name: https://kubernetes.io/zh-cn/docs/concepts/overview/working-with-objects/names#dns-subdomain-names
• [2]ingress-nginx: https://github.com/kubernetes/ingress-nginx
• [3]Ingress: https://kubernetes.io/zh-cn/docs/concepts/services-networking/ingress/