kubernetes - fikt.uklo.edu.mk · a service is a grouping of pods that are running on the cluster....
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Kubernetes
KSpresso 18/11/2016
Ilche Bedelovski, DevOps Engineer in Keitaro
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Kubernetes Introduction
What is Kubernetes?
- Kubernetes is a platform for hosting Docker containers in a clustered environment with multiple Docker hosts.
- Provides container grouping, load balancing, scaling features- Project was started by Google
What is a container?
● Lightweight Linux environment● Hermetically sealed, deployable application● Introspectable, runnable artifact● Recently popularized by Docker
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What is a cluster?
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Kubernetes Architecture
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Pod
Overview of a Pod?
A Kubernetes pod is a group of containers that are deployed together on the same host. If you frequently deploy single containers, you can generally replace the word "pod" with "container" and accurately understand the concept.
Pods operate at one level higher than individual containers because it's very common to have a group of containers work together to produce an artifact or process a set of work.
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Pod
Shared Namespaces, Volumes and Secrets
● Shared Network - All containers share the same network namespace & port space. Communication over localhost is encouraged. Each container can also communicate with any other pod or service within the cluster.
● Shared Volumes - Volumes attached to the pod may be mounted inside of one or more containers.
● Shared Resources - Resource limits such as CPU and RAM are shared between all containers in the pod.
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Pod
Sample pod manifest file in yaml
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apiVersion: v1kind: Podmetadata: name: example-app labels: app: example-app version: v1 role=backendspec: containers: - name: java image: companyname/java ports: - containerPort: 443 volumeMounts: - mountPath: /volumes/logs name: logs - name: logger image: companyname/logger:v1.2.3 ports: - containerPort: 9999 volumeMounts: - mountPath: /logs name: logs - name: monitoring image: companyname/monitoring:v4.5.6 ports: - containerPort: 1234
Pod
Service
Overview of a service?
A service is a grouping of pods that are running on the cluster. Kubernetes services can efficiently power a microservice architecture.
Services provide important features that are standardized across the cluster: load-balancing, service discovery between applications, and features to support zero-downtime application deployments.
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Service
IP Address and Routing
A core design feature of Kubernetes is a routable IP address for every service and pod in the cluster. Assigning IPs this way eliminates port conflicts between applications across the cluster.
This allows any application team to bind to any port they require instead of reconfiguring databases or web servers to listen on non-standard ports.
Each service has a unique IP address and a DNS hostname.
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Service
Load Balancing
● Services are automatically configured to load balance traffic to pods matching the label query. Session affinity can be configured to send traffic to pods by client IP.
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Service
Sample HTTPS service
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Service
kind: ServiceapiVersion: v1metadata: name: Frontend Servicespec: selector: app: webapp role: frontend ports: - name: https protocol: TCP port: 443 targetPort: 443
Replication Controller
Overview of ReplicationController
A replication controller is one of the features of Kubernetes that you'll interact with on a regular basis to launch one or more instances of your applications
Each replication controller has a desired state that is managed by the application deployer.
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Replication Controller
ReplicationController template
In Kubernetes, the base unit of deployment is a pod (intro to pods), which is a group of containers that work together and therefore are logically grouped. The replication controller stores a pod template in order to create new pods if needed.
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Replication Controller
Sample ReplicationControllerapiVersion: v1kind: ReplicationControllermetadata: name: nginx-controllerspec: replicas: 2 selector: role: load-balancer template: metadata: labels: role: load-balancer spec: containers: - name: nginx image: coreos/nginx ports: - containerPort: 80
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Replication Controller
Sample kubectl commands
● kubectl cluster-info● kubectl get namespaces, pods, services● kubectl create -f ./sample-rc.yaml● kubectl describe pod podname● kubectl logs podname
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Sample lab: Launching cluster in AWS and deploy sample service
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