.
Kubernetes Networking
In Kubernetes, networking happens at different levels:
-
- Between containers: implemented as IPC
- Between Pods: implemented by network plugins
- Between Pods and Services: implemented by Service resources
- Between external users and Services: implemented by Services, with the help of Ingress
Network Plugins
- Network plugins are required to implement network traffic between Pods
- Network plugins are provided by the Kubernetes Ecosystem
- Vanilla Kubernetes does not come with a default network plugin, and you’ll have to install it while installing a cluster
- Different plugins provide different features
- Currently, the Calico plugin is commonly used because of its support for features like NetworkPolicy
Services
- Service resources are used to provide access to Pods
- If multiple Pods are used as Service endpoint, the Service will load balance traffic to the Pods
- Different types of Service can be configured:
- ClusterIP: the Service is internally exposed and is reachable only from within the cluster
- NodePort: the Service is exposed at each node’s IP address as a port. The
Service can be reached from outside the cluster at nodeip:nodeport - LoadBalancer: the cloud provider offers a load balancer that routes traffic to
either NodePort- or ClusterIP-based Services - ExternalName: the Service is mapped to an external name that is implemented as a DNS CNAME record
Configuring Services
- Use
kubectl exposeto expose applications through their Pods, ReplicaSet or Deployment (recommended) - Use
kubectl create serviceas an alternative
Demo: Creating Services
kubectl create deploy webshop --image=nginx --replicas=3kubectl get pods --selector app=webshop -o widekubectl expose deploy webshop --type NodePort --port=80kubectl describe svc webshopkubectl get svccurl nodeip:nodeport
Let’s demonstrate creating services:
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[root@k8s cka]# kubectl create deploy webshop --image=nginx --replicas=3 deployment.apps/webshop created [root@k8s cka]# kubectl get pods --selector app=webshop -o wide NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES webshop-7f9fd49d4c-92nj2 1/1 Running 0 32s 10.244.0.24 k8s.example.pl <none> <none> webshop-7f9fd49d4c-kqllw 1/1 Running 0 32s 10.244.0.23 k8s.example.pl <none> <none> webshop-7f9fd49d4c-x2czc 1/1 Running 0 32s 10.244.0.25 k8s.example.pl <none> <none> [root@k8s cka]# kubectl expose deploy webshop --type=NodePort --port=80 service/webshop exposed [root@k8s cka]# kubectl get all --selector app=webshop NAME READY STATUS RESTARTS AGE pod/webshop-7f9fd49d4c-92nj2 1/1 Running 0 92m pod/webshop-7f9fd49d4c-kqllw 1/1 Running 0 92m pod/webshop-7f9fd49d4c-x2czc 1/1 Running 0 92m NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE service/webshop NodePort 10.109.119.90 <none> 80:32064/TCP 27s NAME READY UP-TO-DATE AVAILABLE AGE deployment.apps/webshop 3/3 3 3 92m NAME DESIRED CURRENT READY AGE replicaset.apps/webshop-7f9fd49d4c 3 3 3 92m [root@k8s cka]# kubectl describe svc webshop Name: webshop Namespace: default Labels: app=webshop Annotations: <none> Selector: app=webshop Type: NodePort IP Family Policy: SingleStack IP Families: IPv4 IP: 10.109.119.90 IPs: 10.109.119.90 Port: <unset> 80/TCP TargetPort: 80/TCP NodePort: <unset> 32064/TCP Endpoints: 10.244.0.23:80,10.244.0.24:80,10.244.0.25:80 Session Affinity: None External Traffic Policy: Cluster Events: <none> [root@k8s cka]# kubectl get svc webshop NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE webshop NodePort 10.109.119.90 <none> 80:32064/TCP 82s [root@k8s cka]# curl k8s.example.pl:32064 <!DOCTYPE html> <html> <head> <title>Welcome to nginx!</title> <style> html { color-scheme: light dark; } body { width: 35em; margin: 0 auto; font-family: Tahoma, Verdana, Arial, sans-serif; } </style> </head> <body> <h1>Welcome to nginx!</h1> <p>If you see this page, the nginx web server is successfully installed and working. Further configuration is required.</p> <p>For online documentation and support please refer to <a href="http://nginx.org/">nginx.org</a>.<br/> Commercial support is available at <a href="http://nginx.com/">nginx.com</a>.</p> <p><em>Thank you for using nginx.</em></p> </body> </html> |
Ingress
- Ingress is an API object that manages external access to services in a cluster
- Ingress works with external DNS to provide URL-based access to Kubernetes applications
- Ingress consists of two parts
- A load balancer available on the external network
- An API resource that contacts the Service resources to find out about available back-end Pods
- Ingress load balancers are provided by the Kubernetes ecosystem, different load balancers are available
- Ingress exposes HTTP and HTTPS routes from outside the cluster to Services within the cluster
- Ingress uses the selectorlabel in Services to connect to the Pod endpoints
- Traffic routing is controlled by rules defined on the Ingress resource
- Ingress can be configured to do the following, according to functionality
provided by the load balancer- Give Services externally-reachable URLs
- Load balance traffic
- Terminate SSL/TLS
- Offer name based virtual hosting
based virtual hosting.
Installing the Nginx Ingress Controller
helm upgrade --install ingress-nginx ingress-nginx --repo https://kubernetes.github.io/ingress-nginx --namespace ingress-nginx --create-namespacekubectl get pods -n ingress-nginxkubectl create deploy nginxsvc --image=nginx --port=80kubectl expose deploy nginxsvc
Before we can use the ingress we must ensure that ingress controler is installed. In minikube there is no ingress controller so we must install it using helm.
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[root@k8s cka]# helm upgrade --install ingress-nginx ingress-nginx --repo https://kubernetes.github.io/ingress-nginx --namespace ingress-nginx -- create-namespace Error: "helm upgrade" requires 2 arguments Usage: helm upgrade [RELEASE] [CHART] [flags] [root@k8s cka]# helm upgrade --install ingress-nginx ingress-nginx --repo https://kubernetes.github.io/ingress-nginx --namespace ingress-nginx --create-namespace Release "ingress-nginx" does not exist. Installing it now. NAME: ingress-nginx LAST DEPLOYED: Fri Feb 2 15:08:51 2024 NAMESPACE: ingress-nginx STATUS: deployed REVISION: 1 TEST SUITE: None NOTES: The ingress-nginx controller has been installed. It may take a few minutes for the load balancer IP to be available. You can watch the status by running 'kubectl get service --namespace ingress-nginx ingress-nginx-controller --output wide --watch' An example Ingress that makes use of the controller: apiVersion: networking.k8s.io/v1 kind: Ingress metadata: name: example namespace: foo spec: ingressClassName: nginx rules: - host: www.example.com http: paths: - pathType: Prefix backend: service: name: exampleService port: number: 80 path: / # This section is only required if TLS is to be enabled for the Ingress tls: - hosts: - www.example.com secretName: example-tls If TLS is enabled for the Ingress, a Secret containing the certificate and key must also be provided: apiVersion: v1 kind: Secret metadata: name: example-tls namespace: foo data: tls.crt: <base64 encoded cert> tls.key: <base64 encoded key> type: kubernetes.io/tls [root@k8s cka]# kubectl get all -n ingress-nginx NAME READY STATUS RESTARTS AGE pod/ingress-nginx-controller-6858749594-27tm9 1/1 Running 0 5m15s NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE service/ingress-nginx-controller LoadBalancer 10.98.212.3 <pending> 80:31333/TCP,443:31463/TCP 5m15s service/ingress-nginx-controller-admission ClusterIP 10.105.231.72 <none> 443/TCP 5m15s NAME READY UP-TO-DATE AVAILABLE AGE deployment.apps/ingress-nginx-controller 1/1 1 1 5m15s NAME DESIRED CURRENT READY AGE replicaset.apps/ingress-nginx-controller-6858749594 1 1 1 5m15s [root@k8s cka]# kubectl create deploy nginxsvc --image=nginx --port=80 deployment.apps/nginxsvc created [root@k8s cka]# kubectl expose deploy nginxsvc service/nginxsvc exposed [root@k8s cka]# kubectl get all --selector app=nginxsvc NAME READY STATUS RESTARTS AGE pod/nginxsvc-5f8b7d4f4d-dtrs7 1/1 Running 0 85s NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE service/nginxsvc ClusterIP 10.104.155.180 <none> 80/TCP 72s NAME READY UP-TO-DATE AVAILABLE AGE deployment.apps/nginxsvc 1/1 1 1 85s NAME DESIRED CURRENT READY AGE replicaset.apps/nginxsvc-5f8b7d4f4d 1 1 1 85s |
Installing the Nginx Ingress Controller – part 2
kubectl create ingress nginxsvc --class=nginx --rule=nginxsvc.info/*=nginxsvc:80kubectl port-forward -n ingress-nginx svc/ingress-nginx-controller 8080:80 &(run in background)- Fake DNS (in the real world it won’t be necessary because there were be DNS server.):
echo "127.0.0.1 nginxsvc.info" >> /etc/hosts curl nginxsvc.info:8080
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[root@k8s cka]# kubectl create ingress nginxsvc --class=nginx --rule=nginxsvc.info/*=nginxsvc:80 ingress.networking.k8s.io/nginxsvc created [root@k8s cka]# kubectl port-forward -n ingress-nginx svc/ingress-nginx-controller 8080:80 & [1] 295061 [root@k8s cka]# Forwarding from 127.0.0.1:8080 -> 80 Forwarding from [::1]:8080 -> 80 [root@k8s cka]# vi /etc/hosts [root@k8s cka]# ping nginxsvc.info PING host.minikube.internal (127.0.0.1) 56(84) bytes of data. 64 bytes from localhost (127.0.0.1): icmp_seq=1 ttl=64 time=0.106 ms ^C --- host.minikube.internal ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 0.106/0.106/0.106/0.000 ms [root@k8s cka]# curl nginxsvc.info:8080 Handling connection for 8080 <!DOCTYPE html> <html> <head> <title>Welcome to nginx!</title> <style> html { color-scheme: light dark; } body { width: 35em; margin: 0 auto; font-family: Tahoma, Verdana, Arial, sans-serif; } </style> </head> <body> <h1>Welcome to nginx!</h1> <p>If you see this page, the nginx web server is successfully installed and working. Further configuration is required.</p> <p>For online documentation and support please refer to <a href="http://nginx.org/">nginx.org</a>.<br/> Commercial support is available at <a href="http://nginx.com/">nginx.com</a>.</p> <p><em>Thank you for using nginx.</em></p> </body> </html> [root@k8s cka]# kubectl get all --selector app=nginxsvc NAME READY STATUS RESTARTS AGE pod/nginxsvc-5f8b7d4f4d-dtrs7 1/1 Running 0 20m NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE service/nginxsvc ClusterIP 10.104.155.180 <none> 80/TCP 20m NAME READY UP-TO-DATE AVAILABLE AGE deployment.apps/nginxsvc 1/1 1 1 20m NAME DESIRED CURRENT READY AGE replicaset.apps/nginxsvc-5f8b7d4f4d 1 1 1 20m [root@k8s cka]# kubectl get ingress NAME CLASS HOSTS ADDRESS PORTS AGE nginxsvc nginx nginxsvc.info 80 10m [root@k8s cka]# kubectl describe ingress nginxsvc Name: nginxsvc Labels: <none> Namespace: default Address: Ingress Class: nginx Default backend: <default> Rules: Host Path Backends ---- ---- -------- nginxsvc.info / nginxsvc:80 (10.244.0.29:80) Annotations: <none> Events: Type Reason Age From Message ---- ------ ---- ---- ------- Normal Sync 10m nginx-ingress-controller Scheduled for sync |
Now, let’s edit ngninx svc
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[root@k8s cka]# kubectl edit svc nginxsvc |
and disturb the selector label
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apiVersion: v1 kind: Service metadata: creationTimestamp: "2024-02-02T20:15:42Z" labels: app: nginxsvc name: nginxsvc namespace: default resourceVersion: "98698" uid: f2dfba3e-1c47-443d-a969-a78cd81cf47c spec: clusterIP: 10.104.155.180 clusterIPs: - 10.104.155.180 internalTrafficPolicy: Cluster ipFamilies: - IPv4 ipFamilyPolicy: SingleStack ports: - port: 80 protocol: TCP targetPort: 80 selector: app: nginxSVC # instaed nginxsvc sessionAffinity: None type: ClusterIP status: loadBalancer: {} |
We see that the service is unavailable now:
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[root@k8s cka]# curl nginxsvc.info:8080 Handling connection for 8080 <html> <head><title>503 Service Temporarily Unavailable</title></head> <body> <center><h1>503 Service Temporarily Unavailable</h1></center> <hr><center>nginx</center> </body> </html> |
So, if you have ever problem in ingress you might have investigate what is going on in the service to fix your problem.
Managing Ingress Rules
- ingress rules catch incoming traffic that matches a specific path and optional hostname and connects that to a Service and port
- Use
kubectl create ingressto create rules - Different paths can be defined on the same host
kubectl create ingress mygress --rule="/mygress=mygress:80" --rule="yourgress=yourgress:80"
- Different virtual hosts can be defined in the same Ingress
kubectl create ingress nginxsvc --class=nginx --rule=nginxsvc.info/*=nginxsvc:80 --rule=otherserver.org/*=otherserver:80
IngressClass
- In one cluster, different Ingress controllers can be hosted, each with its own
configuration - Controllers can be included in an IngressClass
- While defining Ingress rules, the
--classoption should be used to implement the role on a specific Ingress controller- If this option is not used, a default IngressClass must be defined
- Set ingressclass.kubernetes.io/is-default-class: true as an annotation on the IngressClass to make it the default
- After creating the Ingress controller as described before, an IngressClass API resource has been created
- Use
kubectl get ingressclass -o yamlto investigate its content
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[root@k8s cka]# kubectl get ingressclass NAME CONTROLLER PARAMETERS AGE nginx k8s.io/ingress-nginx <none> 49m [root@k8s cka]# kubectl get ingressclass -o yaml apiVersion: v1 items: - apiVersion: networking.k8s.io/v1 kind: IngressClass metadata: annotations: meta.helm.sh/release-name: ingress-nginx meta.helm.sh/release-namespace: ingress-nginx creationTimestamp: "2024-02-02T20:09:01Z" generation: 1 labels: app.kubernetes.io/component: controller app.kubernetes.io/instance: ingress-nginx app.kubernetes.io/managed-by: Helm app.kubernetes.io/name: ingress-nginx app.kubernetes.io/part-of: ingress-nginx app.kubernetes.io/version: 1.9.6 helm.sh/chart: ingress-nginx-4.9.1 name: nginx resourceVersion: "98227" uid: 6e638977-b341-46c3-a469-cfb655cd4dac spec: controller: k8s.io/ingress-nginx kind: List metadata: resourceVersion: "" [root@k8s cka]# [root@k8s cka]# kubectl edit ingressclass nginx ingressclass.networking.k8s.io/nginx edited [root@k8s cka]# kubectl get ingressclass -o yaml apiVersion: v1 items: - apiVersion: networking.k8s.io/v1 kind: IngressClass metadata: annotations: ingressclass.kubernetes.io/is-default-class: "true" meta.helm.sh/release-name: ingress-nginx meta.helm.sh/release-namespace: ingress-nginx creationTimestamp: "2024-02-02T20:09:01Z" generation: 1 labels: app.kubernetes.io/component: controller app.kubernetes.io/instance: ingress-nginx app.kubernetes.io/managed-by: Helm app.kubernetes.io/name: ingress-nginx app.kubernetes.io/part-of: ingress-nginx app.kubernetes.io/version: 1.9.6 helm.sh/chart: ingress-nginx-4.9.1 name: nginx resourceVersion: "101308" uid: 6e638977-b341-46c3-a469-cfb655cd4dac spec: controller: k8s.io/ingress-nginx kind: List metadata: resourceVersion: "" |
Configuring Ingress Rules
kubectl get deploymentkubectl get svc webshopkubectl create ingress webshop-ingress --rule="/=webshop:80" --rule="/hello=newdep:8080"sudo vim /etc/hosts127.0.0.1 webshop.info
kubectl get ingresskubectl describe ingress webshop-ingress
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[root@k8s cka]# kubectl get deploy NAME READY UP-TO-DATE AVAILABLE AGE firstnginx 4/4 4 4 2d1h nginxsvc 1/1 1 1 54m webserver 1/1 1 1 7h50m webshop 3/3 3 3 3h19m [root@k8s cka]# kubectl get svc webshop NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE webshop NodePort 10.109.119.90 <none> 80:32064/TCP 107m [root@k8s cka]# kubectl create ingress webshop-ingress --rule="/=webshop:80" --rule="/hello=newdep:8080" ingress.networking.k8s.io/webshop-ingress created [root@k8s cka]# vi /etc/hosts [root@k8s cka]# ping webshop.info PING host.minikube.internal (127.0.0.1) 56(84) bytes of data. 64 bytes from localhost (127.0.0.1): icmp_seq=1 ttl=64 time=0.092 ms 64 bytes from localhost (127.0.0.1): icmp_seq=2 ttl=64 time=0.041 ms ^C --- host.minikube.internal ping statistics --- 2 packets transmitted, 2 received, 0% packet loss, time 1021ms rtt min/avg/max/mdev = 0.041/0.066/0.092/0.026 ms [root@k8s cka]# kubectl get ingress NAME CLASS HOSTS ADDRESS PORTS AGE nginxsvc nginx nginxsvc.info 80 45m webshop-ingress nginx * 80 67s [root@k8s cka]# kubectl describe ingress webshop-ingress Name: webshop-ingress Labels: <none> Namespace: default Address: Ingress Class: nginx Default backend: <default> Rules: Host Path Backends ---- ---- -------- * / webshop:80 (10.244.0.23:80,10.244.0.24:80,10.244.0.25:80) /hello newdep:8080 (<error: endpoints "newdep" not found>) Annotations: <none> Events: Type Reason Age From Message ---- ------ ---- ---- ------- Normal Sync 72s nginx-ingress-controller Scheduled for sync |
As we see the endpoint “newdep” not fount and we must fix it:
Configuring Ingress Rules – part 2
kubectl create deployment newdep --image=gcr.io/google-samples/hello-app:2.0kubectl expose deployment newdep --port=8080kubectl describe ingress webshop-ingress
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[root@k8s cka]# kubectl create deployment newdep --image=gcr.io/google-samples/hello-app:2.0 deployment.apps/newdep created [root@k8s cka]# kubectl expose deployment newdep --port=8080 service/newdep exposed [root@k8s cka]# kubectl describe ingress webshop-ingress Name: webshop-ingress Labels: <none> Namespace: default Address: Ingress Class: nginx Default backend: <default> Rules: Host Path Backends ---- ---- -------- * / webshop:80 (10.244.0.23:80,10.244.0.24:80,10.244.0.25:80) /hello newdep:8080 (10.244.0.30:8080) Annotations: <none> Events: Type Reason Age From Message ---- ------ ---- ---- ------- Normal Sync 9m21s nginx-ingress-controller Scheduled for sync |
Now everything works. Thats how you can use rules.
Lots of useful creating ingress examples you can see when you type:
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[root@k8s cka]# kubectl create ingress -h Examples: # Create a single ingress called 'simple' that directs requests to foo.com/bar to svc # svc1:8080 with a TLS secret "my-cert" kubectl create ingress simple --rule="foo.com/bar=svc1:8080,tls=my-cert" |
Using Port Forwarding
kubectl port-forwardcan be used to connect to applications for analyzing and troubleshooting- It forwards traffic coming in to a local port on the kubectl client machine to a port that is available in a Pod
- Using port forwarding allows you to test application access without the need to configure Services and Ingress
- Use
kubectl port-forward mypod 1235:80to forward local port 1235 to Pod port 80 - To run in the background, use
Ctrl-zor start with a&at the end of thekubectl port-forwardcommand
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[root@k8s cka]# kubectl get pods NAME READY STATUS RESTARTS AGE deploydaemon-zzllp 1/1 Running 0 24h firstnginx-d8679d567-249g9 1/1 Running 0 2d1h firstnginx-d8679d567-66c4s 1/1 Running 0 2d1h firstnginx-d8679d567-72qbd 1/1 Running 0 2d1h firstnginx-d8679d567-rhhlz 1/1 Running 0 32h init-demo 1/1 Running 0 34h lab4-pod 1/1 Running 0 6h57m morevol 2/2 Running 40 (3m53s ago) 20h mydaemon-d4dcd 1/1 Running 0 24h newdep-749c9b5675-2x9mb 1/1 Running 0 10m nginxsvc-5f8b7d4f4d-dtrs7 1/1 Running 0 74m pv-pod 1/1 Running 0 19h sleepy 1/1 Running 24 (31m ago) 35h testpod 1/1 Running 0 2d1h two-containers 2/2 Running 143 (70s ago) 32h web-0 1/1 Running 0 37h web-1 1/1 Running 0 24h web-2 1/1 Running 0 24h webserver-76d44586d-8gqhf 1/1 Running 0 7h57m webshop-7f9fd49d4c-92nj2 1/1 Running 0 3h40m webshop-7f9fd49d4c-kqllw 1/1 Running 0 3h40m webshop-7f9fd49d4c-x2czc 1/1 Running 0 3h40m [root@k8s cka]# kubectl port-forward pods/webserver-76d44586d-8gqhf 1235:80 & [3] 307824 [root@k8s cka]# Forwarding from 127.0.0.1:1235 -> 80 Forwarding from [::1]:1235 -> 80 [root@k8s cka]# curl localhost:1235 Handling connection for 1235 hello world |
It was a siple example of port-forwarding.
Lab: Managing Networking
- Run a deployment with the name apples, using 3 replicas and the Nginx image
- Expose this deployment in such a way that it is accessible on my.fruit
- Use port fowarding to test
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[root@k8s cka]# kubectl create deployment apples --image=nginx --replicas=3 deployment.apps/apples created [root@k8s cka]# kubectl expose deployment apples --port=80 service/apples exposed [root@k8s cka]# kubectl create ingress apples --rule="my.fruit/*=apples:80" ingress.networking.k8s.io/apples created [root@k8s cka]# vim /etc/hosts [root@k8s cka]# cat /etc/hosts 127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6 127.0.0.1 host.minikube.internal nginxsvc.info webshop.info my.fruit 172.30.9.24 control-plane.minikube.internal [root@k8s cka]# curl my.fruit:8080 Handling connection for 8080 <!DOCTYPE html> <html> <head> <title>Welcome to nginx!</title> <style> html { color-scheme: light dark; } body { width: 35em; margin: 0 auto; font-family: Tahoma, Verdana, Arial, sans-serif; } </style> </head> <body> <h1>Welcome to nginx!</h1> <p>If you see this page, the nginx web server is successfully installed and working. Further configuration is required.</p> <p>For online documentation and support please refer to <a href="http://nginx.org/">nginx.org</a>.<br/> Commercial support is available at <a href="http://nginx.com/">nginx.com</a>.</p> <p><em>Thank you for using nginx.</em></p> </body> </html> |
We get Welcome to nginx because we do have a default ingressClass. If you don’t have a default IngressClass this doesn’t work.