Container Virtualization

Containers and Virtualization

• Containers are a form of operating system virtualization, allowing multiple applications to run on a single host machine.
• A container contains all necessary executables, binary code, libraries, and configuration files, but not an operating system, making it lightweight and portable.

Traditional Computer Machine Hardware Virtualization

• Each VM (Virtual Machine) acts as a real computer machine, with its own operating system, virtual hardware, and applications.
• The hypervisor manages the virtual hardware and provides access to the host machine's resources.

Images and Containers

• An image is a lightweight, standalone, executable package that includes everything needed to run a piece of software.
• A container runs an instance of an image, and Docker Hub is a repository of useful images.

Docker Commands

• docker pull is used to retrieve an image from Docker Hub.
• docker images lists all pulled images cached locally.
• docker create creates a new container.
• docker ps lists running containers, and docker start is used to start a container.

Microservices

• Microservices are a distributed software architecture, where a single application is broken down into a suite of small services.
• Each service runs its own process, can be written in any programming language, and is independently deployable and replaceable.

Distributed System and Microservice Architecture

• A distributed system is a network of servers, communicating and coordinating through message passing.
• Microservice architecture is an approach to developing a single application as a suite of small services, each running its own process.

Dockerfile

• A Dockerfile is a text document that contains instructions for building an image.
• The docker build command builds an image from a Dockerfile.

Managing Containers with Kubernetes

• Kubernetes provides facilities for managing containers in a production environment, ensuring no downtime.
• Kubernetes allows for better support for microservices architectures, isolating, deploying, and scaling individual container building blocks.

Kubernetes Components

• A Kubernetes cluster consists of a set of worker machines (nodes) that run containerized applications.
• The control plane manages the worker nodes and Pods, and consists of components such as the API server, scheduler, and kubelet.

Kubernetes Control Plane Components

• The API server validates and configures data for API objects.
• The scheduler watches for newly created Pods and selects a node for them to run on.
• The kubelet takes a set of Pods and ensures that the containers are running and healthy.

Node Components

• The kube-proxy is a network proxy that runs on each node, allowing network communication to Pods.
• The container runtime is responsible for running containers, and Kubernetes supports several container runtimes.

DNS

• Cluster DNS provides DNS records for Kubernetes services, allowing for translation of domain names to IP addresses.