Container technology is changing the way we think about developing and running applications. Containers are lightweight packages of software that include everything it needs to run an application. This includes operating system components as well as libraries and other dependencies. Emerging technologies such as Docker and Kubernetes empowers organizations to deliver quality software with speed and ease.
Contents
- What Is Containerization?
- What Is Docker?
- How Does Docker Work?
- Docker Architecture
- Docker Advantages
- What Is Kubernetes?
- How Does Kubernetes Work?
- Kubernetes Architecture
- Kubernetes Advantages
- Can You Use Docker Without K8s?
- Can You Run K8s Without Docker?
- Benefits of Using Both Docker and K8s Together
- Kubernetes vs. Docker Swarm
What Is Containerization?
Containerization is a way to package an application with its dependencies to deliver the entire stack as one unit. Containerization enables developers to deploy their code in any environment without worrying about incompatibilities. It also eliminates dealing with configuration issues such as setting up shared libraries and paths which could take hours or days using traditional methods.
Containers are easy to manage. They can be started, stopped, moved from one machine to another and scaled up or down, all with very little effort. Containers can also provide a level of isolation. They don’t need their own dedicated hardware resources. This allows for resources to be shared among containers, which improves performance and efficiency.
Why is Containerization popular?
Container technology is becoming popular because it simplifies application deployment and scaling. In the past, developers would need to write scripts to deploy software. Containers make this much easier by packaging an application with all of its dependencies into a standard unit that can then be deployed anywhere on a computer system.
In addition, containers are more lightweight than virtual machines. This means that they take up less space and use less processing power when compared to a traditional server environment. The bottom line: containers offer many benefits for both businesses and developers alike. Enterprises can utilize them to improve IT system performance. Developers can take advantage of containers’ portability to make development easier and faster.
What Is Docker?
Docker is an open-source platform that allows developers to package an application with all of its dependencies into a standardized container for software development. Docker containers are designed to be lightweight, portable, and self-sufficient. They allow you to package up an application with everything it needs, so it will run regardless of the environment it is running in.
Containers are not new; they have been around for decades in the form of chroot on UNIX systems and virtual machines on Windows systems. However, Docker has made containers more accessible by providing a simple way to create them and manage them using standard Linux tools such as cp, tar, and rm. Docker also provides an easy way to share containers with others via public or private registries.
Containers are similar to virtual machines (VMs), but they run on top of the host operating system instead of inside another operating system. This means that they don’t have their own kernel or require special drivers to be installed. This makes them much lighter than VMs. They also have a standard format that allows them to run on any Linux system, regardless of the underlying architecture.
How Does Docker Work?
Docker containers are the runtime that gets created based on a Docker Image. An image is a file that contains all of the information needed to run an application. The image is then used to create a container.
Dockerfiles are a set of instructions for creating an image. They provide all the steps necessary to assemble a container from an intermediate base image. You can think of Dockerfile as your project’s recipe—with carefully chosen ingredients and detailed step-by-step instructions. The Dockerfile consists of three parts:
- A list of commands will be executed to build the container (image).
- A list of environment variables that will be set when running the container (image).
- A list of files and directories that will be copied into the container (image).
An image has several layers. The topmost layer is the rootfs, which contains the filesystem. The next layer is the kernel, which contains all of the operating system’s core components. The third layer is the application, which contains all of your application’s code and dependencies.
Docker images are immutable—once created, they cannot be changed. This means that you can create a new image from an existing image and it will always have the same contents as before. This makes it easy to create a new image from an existing one and reuse it in future projects without having to rebuild it.
Docker Architecture
Docker Engine allows you to develop, assemble, ship, and run applications using the following components:
Docker Daemon
The Docker daemon is a process that works in the background. It manages your containers, does image management, and builds new images for you with one command. It takes care of container naming conflicts by placing them on different hosts, etc. Daemons are run as part of the Docker Engine cluster life cycle—they start when the engine starts up or when it detects its node has been replaced.
Docker Client
The Docker client interacts with the Docker daemon. It creates images, interacts with and manages containers.
Docker Compose
Compose defines and runs multi-container Docker applications. With Compose, you use a YAML file to configure your application’s services. Then, using a single command, you create and start all the services from the configuration file.
Compose works across different operating systems (Linux versions are supported) by reading the same YAML configuration file. As long as all of the containers in an application can communicate with each other over localhost or another host/port specified in the config then docker-compose will work.
Docker Machine
The Docker Machine tool allows you to create virtual machines (VMs) that run on top of the Linux kernel provided by the operating system vendor (e.g., Red Hat Enterprise Linux). This allows you to create VMs that are based on other operating systems such as Windows Server or Ubuntu without having to install them yourself or use third-party tools.
Docker Engine REST API
The Docker Engine REST API provides endpoints for external systems to interact with containers. The goal is to facilitate communication between these systems and containers using standard protocols like JSON over HTTPS.
Docker Command Line Interface
Docker CLI is a command-line interface that can be used to control and manage Docker. It enables you to deploy your applications as containers, using the docker build, docker commit or other commands.
Docker Advantages
One of the most important benefits of Docker containers is that they are highly portable. They can run any computer or server. This is because Docker containers run as processes in the Linux kernel. This means no extra installation process for each machine is needed.
Containers also ensure that code related to different apps is isolated from one. So if there’s a vulnerability in your application it won’t affect other apps on the same server. Lastly, Docker has built-in security features such as mandatory access control (MAC), seccomp profiles, and user namespaces.
What Is Kubernetes?
Kubernetes is an open-source container orchestration system. Container orchestration is a process in which the system automatically manages different containerized applications and their respective resources, ensuring that they do not conflict or overlap with other running processes.
How Does Kubernetes Work?
Kubernetes performs CPU allocation, memory limits, storage space allocations, etc. to each container. It schedules containers across nodes in the cluster, keeps track of them, and makes sure that they are running properly. It also provides mechanisms for communicating with other clusters or external systems such as databases.
Kubernetes Architecture
Kubernetes contains two main components: a Master node and a Worker Node. Below are the main components of the master node:
etcd Cluster
The etcd cluster is a distributed key-value store that provides a reliable way to store configuration data and other states.
Kubelet
The Kubelet is the primary node agent for cluster management. It watches containers to make sure they are running and healthy restarts them if necessary and ensures that any containerized application can connect with other components of your system (like storage or another instance of itself) as needed.
Kubelet-proxy
The Kubernetes proxy runs on each Node in a cluster—it maintains connections between Pods (containers), Services, external endpoints like Docker Hub repositories or microservices architectures outside the cluster. It load balances traffic across those connections; provides health checks on all services.
Kube-controller-manager
The kube-controller-manager runs as a background process on each node in the cluster. It communicates with other controllers to achieve the desired state from the system. It also provides an API that may be used in third-party applications or external components, such as kubelets.
Kubelet-scheduler
The scheduler runs on each node and manages pods, scheduling pods to run on nodes and monitoring pod status.
Below are the main components found on a (worker) node:
kubelet
A Kubernetes container runtime that handles the containers on a node. It is responsible for providing all of the functionality required to manage your pods and services, including (but not limited to) pulling images, starting containers when necessary to scale up or down with demand, maintaining application health(such as by restarting crashed instances), attaching storage volumes from provisioners such as Docker Volumes API or Cattle Volume Driver), exposing IP addresses via Services (if configured)
Kube-proxy
Kube-proxy is a node agent that runs on each machine to provide an interface for Kubernetes services. Kube-proxy accepts connections from kubectl proxy and handles all the proxying of TCP traffic between the cluster, upstreams (such as Docker or OpenShift), and clients.
Kubelet
Kubelet is the agent that runs on each node in a Kubernetes cluster. It talks to various components of the system, keeps track of which containers are running where, and does all local setup for containers. The kubelet assigns IPs to new pods or services as they are created.
Kubernetes Advantages
Kubernetes handles much of the complexities of managing containers. This simplifies maintenance and frees developers to work on more value-added tasks. Additional benefits include:
Increased Performance: Kubernetes scales horizontally, so the more nodes you add to your cluster, the better!
Standardized Configuration Management: With kubectl run commands and templates for Dockerfile options like ports and volumes. It’s easy to deploy new clusters with a consistent configuration.
Improved Security and Stability Through Larger Resource Pools: The larger resource pools of CPUs/memory per pod give containers access to all available system resources without any contention or interference from other pods on the same node. This improves both stability as well as security by limiting exposure points in an environment where multiple services are running on a single node. If one service gets compromised it doesn’t automatically lead to compromise of another service.
Single Cluster Domain Controller For Administering Services And Applications Across All Clusters In Your Organization: A universal control plane ensures everyone has visibility into what’s happening across their entire infrastructure no matter who manages them or how they manage them. Everything is logged centrally which makes administration simpler.
Can You Use Docker Without K8s?
Docker can be used without Kubernetes. In this scenario, Docker swarm performs orchestration. Swarm is Docker’s native clustering system. Docker Swarm turns a pool of Docker engines into a single logical unit, making it simple to scale applications across multiple hosts and automatically heal itself from node failures.
Docker swarm works by orchestrating a cluster of Docker Engines to behave like one large, virtual single host. These engines communicate with each other using SwarmKit. It creates a cluster that can allocate tasks or workload dynamically among the individual nodes in the swarm depending on resource availability.
Benefits of Docker Swarm
Outside of being Docker-native, Swarm comes with a host of benefits. The additional benefits include:
Speed: You can spin up containers faster due to their lightweight nature
Size: The size of a swarm is only limited by your storage capacity meaning you get higher availability
Extendable: When you use docker swarm mode, it supports single-node swarms which makes it easier for developers or companies who want to test new ideas without compromising their production environment
Scaling: Container clusters scale automatically when nodes are added or removed from them automagically based on the need
Customizable: Swarm allows developers/companies full control over what they deploy where they deploy it making deployment pipelines smoother.
Easy To Use: Docker swarm is easy to use and deploy. It’s a simple command-line tool that you can run on your laptop or server.
Easy to Manage: You can easily manage your containers with docker swarm. You can create, join and leave a swarm without any downtime
Easy to Scale: Docker swarm scales automatically based on the number of nodes in the cluster. This means you don’t have to worry about scaling up or down your cluster when you need more or fewer resources
Easy To Secure: Docker Swarm has built-in security features that allow you to control access and permissions for each container in the cluster
Easy to Monitor: You can easily monitor your containers with the docker stats command which gives you information about each container in the cluster including CPU usage, memory usage, network traffic, etc.
Can You Run K8s Without Docker?
Kubernetes can not function without a container runtime. Docker is one of the various platforms used for containerization, but it’s not the only platform. You don’t need to use Docker exclusively; any other compatible option will work.
Benefits of Using Both Docker and K8s Together
Kubernetes is a container orchestration system for managing docker containers. Docker has been designed to provide an additional layer of control and management over the container lifecycle, however, Kubernetes provides that functionality in a way that’s more suited to large-scale deployments or to scale-out applications with high availability requirements.
Kubernetes vs. Docker Swarm
Docker Swarm is the native clustering solution for Docker. It provides built-in load balancing, high availability through an integrated management layer that includes support from major cloud providers such as AWS CloudFormation templates and Google GKE integration. Swarm also integrates with Puppet. Kubernetes is a complete system that automates control of containerized application programming interface (API) deployments into clusters of Linux containers running both within a single data center or between multiple data centers across geographies.
Kubernetes and Docker are robust technologies that simplify application deployment. Packaging applications into “containers” makes for more secure, scalable, and resilient systems. Using them together empowers teams to deliver applications with less maintenance overhead so they can focus on more important tasks.