Container Orchestration with Kubernetes

Containers and Orchestration

• Containers are needed to solve several challenges, such as compatibility and dependency problems, long setup times, and different Dev/Test/Prod environments.
• A container consists of an entire runtime environment: an application, its dependencies, libraries, and other binaries, and configuration files needed to run it, bundled into one package.

Containers vs Virtual Machines

• Containers run on top of the host OS kernel, whereas Virtual Machines run their own OS kernel.
• Containers share the host OS kernel, whereas Virtual Machines have their own OS kernel.

Docker Overview

• Docker is a container runtime that allows you to package, ship, and run applications in containers.
• Docker consists of:
  • Docker daemon (dockerd) that listens for Docker API requests and manages Docker objects.
  • Docker client (docker) that sends commands to dockerd.
  • Docker registry that stores Docker images.
  • Docker Hub, a public registry that anyone can use.

Containers Orchestration

• Containers orchestration is necessary to manage the lifecycle of containers, especially in large, dynamic environments.
• Orchestration automates the scheduling, deployment, networking, scaling, health monitoring, and management of containers.
• A use case for containers orchestration is when you have multiple applications running on a single server and need to scale, deploy, and manage them.

Limits of Containers without Orchestration

• Managing a small number of containers on a few hosts using Docker CLI is adequate, but falls short of automating complex deployments on multiple hosts.

Kubernetes

• Kubernetes is an open-source container orchestration engine for automating deployment, scaling, and management of containerized applications.
• Kubernetes architecture consists of:
  • Node: a virtual or physical machine that runs containers.
  • Cluster: a set of nodes that run containerized applications.
  • Master Node: a node that controls and manages a set of worker nodes.
  • API Server: validates and configures data for API objects.
  • etcd: a consistent and highly-available key-value store used as Kubernetes' backing store.
  • Kubelet: an agent that runs on each node and ensures containers are running in a pod.
  • Container Runtime: software that runs containers, such as Docker, containerd, or CRI-O.
  • Controller: control loops that watch the state of the cluster and make changes where needed.
  • Scheduler: selects a node for newly created pods to run on.