Kubernetes

• provides a reliable and scalable platform for running containerized workloads.
• the OS of the cloud native world.

Control Plane

• the cluster's brain
• runs on master nodes.
• runs all the tasks required for Kubernetes to do its jobs, such as
  • scheduling containers,
  • managing services,
  • serving API requests.

Control Plane Components

• kube-apiserver, frontend of control plane.
• etcd, stores all its information.
• kube-scheduler, decides where to run pods.
• kube-controller-manager, runs resource controllers, such as Deployments.
• cloud-controller-manager, manages cloud resources such as load balancers and volumes.

Worker Nodes

• cluster members
• run user workloads
• Best practice: distribute worker nodes to multiple availability zone.

Worker Node Components

• kubelet
  • drive the container runtime to start workloads
  • monitor workload status
• kube-proxy, routes requests
  • in-between pods and other nodes.
  • in-between pods and the internet.
• container runtime
  • actually starts and stops containers.
  • handles container communications.
  • can be Docker, rkt, CRI-O.

High Availability

• The cluster works properly if any individual node fails, or shut down, or one of the control plane components stops running, or network partition.
• etcd is replicated across multiple nodes.
• Control plane disaster ≠ Application down.
• Kubernetes reschedule pods to somewhere else if worker node is down.
• Kubernetes might not be able to reschedule if a large number of nodes fail at once due to insufficient resources.

Kubernetes is HARD

• Managing your own clusters requires a significant investment of time, effort, and expertise. Even then, you can still get it wrong, in terms of people, skills, engineering time, maintenance, and troubleshooting.

• After the initial setup, you need to consider HA, security, and so on.

• Kubernetes is simple and well-designed, but it has to deal with very complex situation and leads to complex software.

• Give managed Kubernetes services a shot: GKE, EKS, AKS, HKS, OpenShift,

• Give turnkey Kubernetes services a shot: Stackpoint, CKE.

• Want to install it by yourself anyway? Try kops, kubespray, tk8.

  kelseyhightower/kubernetes-the-hard-way

• Run less software philosophy says you should outsource undifferentiated heavy lifting. Let cloud vendors do the hard work. Use managed Kubernetes if you can.