Kubernetes: Orchestrate Your Containers
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Kubernetes: Orchestrate your containers Environment: KVM Hypervisor. Red Hat Enterprise Atomic Host 7.1 qcow2 image All in one configuration Pod, replication controller and service manifest file are available under /root folder in the qcow2 image. Required container images are included in the qcow2 image. Activities: 1. Setting up the kubernetes nodes 2. Deploying multi-container application 3. Scaling up the number of pods 4. Rolling updates Importing the Virtual Machine image Copy the image rhel-atomic-cloud-7.1-0.x86_64.qcow2 and atomic0-cidata1.iso to your desktop or laptop. Unzip the archive 1. Open a terminal and execute the command virt-manager as the root user. 2. Hit the icon for “Creating a new virtual machine” 3. In the new Window, enter the following details Name: Kubernetes Select “Import Existing disk image” Hit next 4. In the new window, hit the browse button and point to the location of the image rhel-atomic-cloud-7.1- 0.x86_64.qcow2. Select the OS type as Linux and version as Fedora . Click the forward button 5. Allocate a minimum of 1024 MB RAM and 1 cpus. Hit forward. Select the option “Customize Configuration Before Install” and hit finish 6. Add a hardware -> storage->cdrom and point the iso to atomic0-cidata1.iso 7. Make sure the NIC device model is set as virtio 8.Click finish. 9. Hit apply and click on the Begin installation option, VM will be spawned and you will notice the login screen in the VM console Kubernetes services: The kubernetes relies on a set daemons: apiserver, scheduler, controller, kubelet, proxy. These daemons/services are managed by systemd and the configuration resides in a central location: /etc/kubernetes. The services are split according to the intended role in the kubernetes environment. For this demo, we will use all in one node configuration. All the below services should be started on the virtual machine. Kubernetes Master Services 3 services that constitutes kubernetes master are kube-apiserver kuber-controller-manager kube-scheduler This host should be configured to run all the above services running. Another essential service that the master node should have is etcd Kubernetes Node Services (formerly known as Minion) Following services should be configured to run in the slave 1. Kubelet 3. docker 2. kube-proxy Activity 1: Setting up the kubernetes cluster Login as the root user with the password “atomicrhte”. Since both Kubernetes Master and Minion services are running on the local system, you don't need to change the Kubernetes configuration files. Master and minion services will point to each other on localhost and services are made available only on localhost Starting Kubernetes For starting all the Kubernetes Master Services, use the below command # for SERVICES in etcd kube-apiserver kube-controller-manager kube-scheduler do systemctl restart $SERVICES systemctl enable $SERVICES systemctl status $SERVICES done For starting all the Kubernetes Node Services, use the below command # for SERVICES in docker kube-proxy.service kubelet.service; do systemctl restart $SERVICES systemctl enable $SERVICES systemctl status $SERVICES done Verify the configuration Using netstat/ss verify the required services are up and listening # netstat -tulnp | grep -E "(kube)|(etcd)" or using ss # ss -tulnp | grep -E "(kube)|(etcd)" Test etcd service curl -s -L http://localhost:4001/version etcd 0.4.6 Verify Kubernetes configuration # kubectl get nodes NAME LABELS STATUS 127.0.0.1 <none> Ready If kubernetes is configured properly, kubectl get nodes should list localhost in “ready” status Activity 2: Deploying multi-container application Logical diagram 1. Understanding Mariadb ReplicationController mainfest file Under /root folder, open the file 1_mariadb_rc.yaml using vi and then observe the following line 1 id: "db-controller" 2 kind: "ReplicationController" 3 apiVersion: "v1beta1" Keyword “Kind” helps one to identify what type of resource it is. Here kind refers to “ReplicationController”. Mariadb service here will be started via the ReplicationController. For this demo, we will be using apiversion v1beta1 4 desiredState: 5 replicas: 1 6 replicaSelector: 7 selectorname: "db" Line number 5 (replicas 1) tells kubernetes to always run one instance of the pod. If the pod dies, then start the pod again. ReplicaSelector identifies the set of pods that this replicationcontroller is responsible for 13 containers: 14 - name: "db" 15 image: "backend-mariadb" 16 ports: 17 - containerPort: 3306 Line 16 tells kubernetes to use the container image backend-mariadb. If this image is not locally available, it will first search Red Hat repository. If the image is not available in the Red Hat repository, then it will search docker hub. Docker daemon can be configured to use a custom or private registry as well. 18 labels: 19 name: "db" 20 selectorname: "db" 21 labels: 22 name: "db-controller" Kubernetes will label the mariadb pods as “db” (line 19) and line 21 labels the replicationcontroller as db- controller 2. Starting the Mariadb replicationController # kubectl create -f 1_mariadb_rc.yaml The above command will start the replicationController “maria” and the corresponding mariadb pod 3. Verify whether mariadb pod has been started # kubectl get pods If you notice the status of pod as “Pending”, execute the same command again. Within a few seconds, the pod status should change as running -bash-4.2# kubectl get pods POD IP CONTAINER(S) IMAGE(S) HOST LABELS STATUS 029 172.17.0.23 db backend-mariadb 127.0.0.1/ name=db,selectorname=db Running From the above output, note the values under the column LABELS and compare it with the Mariadb manifest file 1_mariadb_rc.yaml. Label can be used for querying or selecting the pods The container has received an IP from the docker bridge docker0 # kubectl get rc CONTROLLER CONTAINER(S) IMAGE(S) SELECTOR REPLICAS maria mariadbapp mariadb:latest name=mariadbpod 1 Use the above command to query the replicationConroller information. Number of replicas for mariadb pod is 1. 4. Understanding mariadb service manifest file under /root folder, open the file “2_mariadb_serv.yaml” 1 id: "db-service" 2 kind: "Service" 3 apiVersion: "v1beta1" 4 port: 3306 5 selector: 6 name: "db" 7 labels: 8 name: "db" kind here is of type “service” (line 2). This service definition will forward incoming request to port 3306 to pods that are labeled as “db” 5. Deploying the mariadb services # kubectl create -f 2_mariadb_serv.yaml 6. Verify the status of mariadb services #kubectl get services NAME LABELS SELECTOR IP PORT kubernetes component=apiserver,provider=kubernetes <none> 10.254.110.210 443 kubernetes-ro component=apiserver,provider=kubernetes <none> 10.254.160.132 80 db-service name=db name=db 10.254.66.155 3306 The frontend app should use the IP “10.254.24.214” as the service ip address when trying to connect to the backend database. This IP range is taken from the directive “KUBE_SERVICE_ADDRESSES=" mentioned in the configuration file “/etc/kubernetes/apiserver”. This address range is used for services 7. Deploying the frontend application Frontend pod manifestation file is available under /root as “3_frontend_rc.yaml”. It is similar to mariadb Review the replicationController definition for the front end python application and then deploy it. Note the replica is set to two. # kubectl create -f 3_frontend_rc.yaml 8. Deploy the Frontend Service end point Review the frontend service file “4_front_svc.yaml” available under /root 1 kind: "Service" 2 id: "webserver-service" 3 apiVersion: "v1beta1" 4 port: 80 5 publicIPs: 6 - 192.168.100.166 7 selector: 8 name: "webserver" 9 labels: 10 name: "webserver" Line 6: Replace the IP with the node's ip. This is optional. By defining a public IP address, we’re telling the kubernetes that we want this service reachable on these particular IP addresses. # kubectl create -f 4_front_svc.yaml 9. Testing the application If all the pods are deployed properly, the output of “kubectl get pods” should be similar to one shown below -bash-4.2# kubectl get pods POD IP CONTAINER(S) IMAGE(S) HOST LABELS STATUS 029 172.17.0.23 db backend-mariadb 127.0.0.1/ name=db,selectorname=db Running 838 172.17.0.24 apache-frontend frontend-apache 127.0.0.1/ name=webserver,selectorname=webserver,uses=db Running 838 172.17.0.25 apache-frontend frontend-apache 127.0.0.1/ name=webserver,selectorname=webserver,uses=db Running Two frontend pods and one backend pod should be running. Verify whether the frontend pod is accessible. Use the IP of the frontend pod shown in the above command output # curl http://172.17.0.24 The Web Server is Running Test the backend connectivity from the front end application. It connects to the database and prints the table contents. # curl http://172.17.0.24/cgi-bin/action -- <h2>RedHat rocks</h2> -- Frontend service should be accessible via the publicIP (here node IP as well) # curl http://192.169.100.166/cgi-bin/action -- <h2>RedHat rocks</h2> -- Activity 3. Scaling up the number of pods Frontend replicationcontroller was configured to start with two replicas initially. Update the file 3_frontend_rc.yaml so that it now starts 5 pods/replicas 1 id: "webserver-controller" 2 kind: "ReplicationController" 3 apiVersion: "v1beta1" 4 desiredState: 5 replicas: 5-- Change line number 5 from “2” to “5”. Execute the below command after making the change # kubectl update -f 3_frontend_rc.yaml You can also scale directly using the below command # kubectl resize --replicas=5 replicationcontrollers webserver-controller This should start three more additional frontend