Kubernetes

Kubernetes

Kubernetes is an open source system for managing containerized applications across multiple hosts; providing basic mechanisms for deployment, maintenance, and scaling of applications.

All following tasks could be done with ansible from playbook repositories: http://git.altlinux.org/people/obirvalger/public/ansible-k8s.git, http://git.altlinux.org/people/obirvalger/public/ansible-test-nginx.git.

Preparing

Need one master node and some (three in this example) slave nodes. The following packages should be installed on the nodes:

# apt-get install docker-ce kubernetes-kubeadm kubernetes-kubelet cri-tools

Full network connectivity among all machines in the cluster should be present.

Cluster deployment

1. The following command initializes cluster when running on master:

   # kubeadm init --pod-network-cidr=10.244.0.0/16 --ignore-preflight-errors=SystemVerification.

   Flags explanation:

   --pod-network-cidr=10.244.0.0/16 - internal net, this cidr is needed by Flannel;

   --ignore-preflight-errors=SystemVerification - do not fail if too new docker version is installed.

   At the end of the previous command output would be next command:

   kubeadm join <ip_address>:<порт> --token <token> --discovery-token-ca-cert-hash sha256:<hash>.

2. Configuring kubernetes to work from user (not from root).
   1. Create directory ~/.kube:

      $ mkdir ~/.kube;

   2. Copy config:

      # cp /etc/kubernetes/admin.conf ~<username>/.kube/config;

   3. Change config owner:

      # chown <username>: ~<username>/.kube/config.

3. Then join other nodes to master:

   # kubeadm join <ip_address>:<port> --token <token> --discovery-token-ca-cert-hash sha256:<hash> --ignore-preflight-errors=SystemVerification.

   Nodes could be verified via:

   $ kubectl get nodes -o wide

   Approximate output:

   NAME      STATUS    ROLES     AGE       VERSION   INTERNAL-IP   EXTERNAL-IP   OS-IMAGE      KERNEL-VERSION        CONTAINER-RUNTIME
   docker1   Ready     <none>    4h        v1.11.2   10.10.3.23    <none>        ALT Regular   4.17.14-un-def-alt1   docker://Unknown
   docker2   Ready     <none>    4h        v1.11.2   10.10.3.120   <none>        ALT Regular   4.17.14-un-def-alt1   docker://Unknown
   docker3   Ready     <none>    4h        v1.11.2   10.10.3.157   <none>        ALT Regular   4.17.14-un-def-alt1   docker://Unknown
   k8s       Ready     master    4h        v1.11.2   10.10.3.227   <none>        ALT Regular   4.17.14-un-def-alt1   docker://Unknown
   

4. Installing pod network addon:

   $ kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml.

   Verifying network work:

   $ kubectl get pods --namespace kube-system.

   Approximate output:

   NAME                          READY     STATUS    RESTARTS   AGE
   coredns-78fcdf6894-6trk7      1/1       Running   0          2h
   coredns-78fcdf6894-nwt5l      1/1       Running   0          2h
   etcd-k8s                      1/1       Running   0          2h
   kube-apiserver-k8s            1/1       Running   0          2h
   kube-controller-manager-k8s   1/1       Running   0          2h
   kube-flannel-ds-894bt         1/1       Running   0          2h
   kube-flannel-ds-kbngw         1/1       Running   0          2h
   kube-flannel-ds-n7h45         1/1       Running   0          2h
   kube-flannel-ds-tz2rc         1/1       Running   0          2h
   kube-proxy-6f4lm              1/1       Running   0          2h
   kube-proxy-f92js              1/1       Running   0          2h
   kube-proxy-qkh54              1/1       Running   0          2h
   kube-proxy-szvlt              1/1       Running   0          2h
   kube-scheduler-k8s            1/1       Running   0          2h
   

Note, that coredns should be in the Running state. Number of kube-flannel and kube-proxy accords to number of nodes (four in these example).

Test launch of nginx

1. Lets create Deployment:

   $ kubectl apply -f https://k8s.io/examples/application/deployment.yaml;

2. Then create service, to get external access to the our application;

   Save the following configuration to the file nginx-service.yaml:

   apiVersion: v1
   kind: Service
   metadata:
     name: nginx
     labels:
       app: nginx
   spec:
     type: NodePort
     ports:
     - port: 80
       targetPort: 80
     selector:
       app: nginx
   

3. Run the service:

   $ kubectl apply -f nginx-service.yaml.

4. Get its port:

   $ kubectl get svc nginx

   Approximate output:

   NAME      TYPE       CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
   nginx     NodePort   10.108.199.141   <none>        80:32336/TCP   4h
   

5. And verify working of our application:

   $ curl <ip_address>:<port>, где

   ip_address - is the ip address of any node, and port gets from service. Example of command: curl 10.10.3.120:32336.