Docker vs. Kubernetes

What is Docker?

Docker is an open source containerization platform. Basically, it’s a toolkit that makes it easier, safer and faster for developers to build, deploy and manage containers. Although it began as an open source project, Docker today also refers to Docker, Inc., the company that produces the commercial Docker product. Currently, it is the most popular tool for creating containers, whether developers use Windows, Linux or MacOS.

In fact, container technologies were available for decades prior to Docker’s release in 2013. In the early days, Linux Containers (or LXC) were the most prevalent of these. Docker was built on LXC, but Docker’s customized technology quickly overtook LXC to become the most popular containerization platform.

Among Docker’s key attributes is its portability. Docker containers can run across any desktop, data center or cloud environment. Only one process can run in each container, so an application is able to run continuously while one part of it is undergoing an update or being repaired.

Some of the tools and terminology commonly used with Docker include the following:

• Docker Engine: The runtime environment that allows developers to build and run containers.
• Docker file: A simple text file that defines everything needed to build a Docker container image, such as OS network specifications and file locations. It’s essentially a list of commands that Docker Engine will run in order to assemble the image.
• Docker Compose: A tool for defining and running multi-container applications. It creates a YAML file to specify which services are included in the application and can deploy and run containers with a single command via the Docker CLI.

Other Docker API features include the ability to automatically track and roll back container images, use existing containers as base images for building new containers and build containers based on application source code. Docker is backed by a vibrant developer community that shares thousands of containers across the internet via the Docker Hub.

But while Docker does well with smaller applications, large enterprise applications can involve a huge number of containers — sometimes hundreds or even thousands — which becomes overwhelming for IT teams tasked with managing them. That’s where container orchestration comes in. Docker has its own orchestration tool, Docker Swarm, but by far the most popular and robust option is Kubernetes.

How Does Docker Work

To understand how Docker works, you need to get acquainted with its main components and the role they play in the platform:

• The Docker daemon is a service that runs on the host and listens to Docker API requests. This continuous process manages Docker objects and communicates with other daemons.
• The Docker client is a component that provides a command line interface (CLI) for interacting with Docker and instructing dockerd which commands to carry out.
• Docker objects are elements necessary to construct the applications. They include Docker images, containers, volumes, networks, and other objects.
• Docker Registries are content delivery systems that store Docker images. You can set up and use a private registry or use Docker Hub, a public registry from which Docker pulls images by default.

The process begins with a script of instructions, called a Dockerfile. The file outlines how to create a Docker image and automatically executes the outlined commands.

All Docker containers are created from Docker images representing templates of an application at a specific point in time. The source code, dependencies, libraries, tools, and other files required for the application to run are packages into the image.

Once you spin up a Docker container from the specified Docker image, you can use it as a stable environment for developing and testing software. Containers represent portable, compact, isolated run-time environments that you can easily start up. As quickly as you can spin up new containers, you can also delete old ones.

When do I use Docker?

Using Docker, you can move your application from a local development server to a production server without any error. Docker is highly recommended for all application development. Docker offers so many tools (software such as NodeJS, PHP, Java, Any Database, etc) as images.

So you can easily install the needed software using Docker and create a container for the application development. Databases are a great fit for Docker. You can easily move the database container from one machine to another without any problem. If you are developing a complex software application then Docker will save your life by automating the code deployment.

Advantages and Drawbacks of Docker

Take a look at the main pros and cons of using Docker.

Advantages:

• It is simple and fast to spin up new container instances.
• Consistency across multiple environments.
• Isolated environments simplify debugging.
• Large community support.
• Containers are lighter and use less resources than virtual machines.
• The platform supports CI/CD.
• The ability to automate repetitive tasks.

Disadvantages:

• Possible security issues if containers are not secured properly.
• Potential performance issues in non-native environments.
• Since containers share the host kernel, they are not entirely isolated environments.
• Cross-platform compatibility limitations.
• Not suitable for applications that require rich interfaces.

Build and Deploy Containers With Docker

Docker helps developers create and deploy software within containers. It’s an open source tool that allows you to “Build, Ship, and Run applications, Anywhere.”

With Docker, you can create a file called a Dockerfile. Dockerfile then defines a build process, and when fed to the ‘docker build’ command, it will create an immutable image. You can think of the Docker image as a snapshot of the application and its dependencies. When a user wants to start it up, they use the ‘docker run’ command to run it anywhere the docker daemon is supported and running.

Docker also has a cloud-based repository known as Docker Hub. You can use Docker Hub as a registry to store and distribute the container images you build.

What is Kubernetes?

Kubernetes is an open source container orchestration platform for scheduling and automating the deployment, management and scaling of containerized applications. Containers operate in a multiple container architecture called a “cluster.” A Kubernetes cluster includes a container designated as a “master node” that schedules workloads for the rest of the containers — or “worker nodes” — in the cluster.

The master node determines where to host applications (or Docker containers), decides how to put them together and manages their orchestration. By grouping containers that make up an application into clusters, Kubernetes facilitates service discovery and enables management of high volumes of containers throughout their lifecycles.

Google introduced Kubernetes as an open source project in 2014. Now, it’s managed by an open source software foundation called the Cloud Native Computing Foundation. Designed for container orchestration in production environments, Kubernetes is popular due in part to its robust functionality, an active open source community with thousands of contributors and support and portability across leading public cloud providers (e.g., IBM Cloud, Google, Azure and AWS).

Key Kubernetes functions include the following:

• Deployment: Schedules and automates container deployment across multiple compute nodes, which can be VMs or bare-metal servers.
• Service discovery and load balancing: Exposes a container on the internet and employs load balancing when traffic spikes occur to maintain stability.
• Auto-scaling features: Automatically starts up new containers to handle heavy loads, whether based on CPU usage, memory thresholds or custom metrics.
• Self-healing capabilities: Restarts, replaces or reschedules containers when they fail or when nodes die, and kills containers that don’t respond to user-defined health checks.
• Automated rollouts and rollbacks: Rolls out application changes and monitors application health for any issues, rolling back changes if something goes wrong.
• Storage orchestration: Automatically mounts a persistent local or cloud storage system of choice as needed to reduce latency — and improve user experience.

How Does Kubernetes Work?

The basic Kubernetes components and their role in this orchestration tool include the following:

• A Kubernetes cluster is a set of node machines for running containerized applications. The cluster consists of a control plane and one or more computing machines.
• The manifest file is a basic file that defines the general framework for a particular Kubernetes cluster and instructs the software on how you want your cluster to look like.
• Kubectl is the command-line interface used for communicating with the API server. It provides instructions to the server and directly manages resources, adding and removing containers when needed.
• The master node is responsible for load balancing workloads and establishing and maintaining communication inside the cluster. Additionally, it assigns and administers tasks to Worker Nodes.
• Worker nodes are machines for deploying containerized workloads and storage volumes. A Kubernetes cluster consists of a single Master Node and multiple Worker Nodes, where each has its task.
• A pod is the simplest Kubernetes object that consists of multiple containers that belong to the same node. Containers deployed within the same pod share resources such as their hostname, IP address, and IPC.

Note: This is a feature-rich orchestration tool. Take a look at the best Kubernetes practices outlined in this article that will help you create stable and efficient clusters.

Each Kubernetes cluster has two parts — the control plane and the nodes (physical or virtual machines). While the control plane manages the cluster to ensure it is in the prescribed state, the nodes run pods consisting of multiple containers running an application.

Developers instruct the control plane which commands to run on the nodes. The control plane then assigns the task to a particular node. Finally, a pod inside the node is automatically chosen to perform the task based on the workload and resources required.

Learn more about clusters, nodes, and automating container processes in our introduction to Kubernetes Architecture.

When do I use Kubernetes?

1. When you want to monitor the health and performance of multiple containers.
2. To deploy 1000s of containers in a single command.
3. To detect fails/crashes of containers and fix them.
4. To scale up and scale down the number of containers.
5. For advanced networking between containers hosted across the cluster.
6. To customize deployment of containers.
7. To support all cloud service environments: many cloud providers offer built-in Kubernetes services.
8. To upgrade all the containers in a single command.
9. To roll back container updates if something goes wrong.
10. To support a wide variety of authentication and authorization services.

Advantages and Drawbacks of Kubernetes

Take a look at the main advantages and disadvantages of Kubernetes.

Advantages:

• Simplifies rolling updates, canary deployments, horizontal autoscaling, and other deployment operations.
• Automated processes help speed up delivery and improve general productivity.
• Its ability to run across multiple environments eliminates infrastructure lock-ins.
• Provides the foundation for working with cloud-native apps.
• Its features support high availability, low downtime, and overall more stable applications.

Disadvantages:

• The complexity of the platform is not efficient for smaller applications.
• Migrating a non-containerized application onto the Kubernetes platform could be quite challenging.
• Due to its complexity, there is a steep learning curve that may initially reduce productivity.

Kubernetes and Docker: Finding your best container solution

Although Kubernetes and Docker are distinct technologies, they are highly complementary and make a powerful combination. Docker provides the containerization piece, enabling developers to easily package applications into small, isolated containers via the command line. Developers can then run those applications across their IT environment, without having to worry about compatibility issues. If an application runs on a single node during testing, it will run anywhere.

When demand surges, Kubernetes provides orchestration of Docker containers, scheduling and automatically deploying them across IT environments to ensure high availability. In addition to running containers, Kubernetes provides the benefits of load balancing, self-healing and automated rollouts and rollbacks. Plus, it has a graphical user interface for ease of use.

For companies that anticipate scaling their infrastructure in the future, it might make sense to use Kubernetes from the very start. And for those already using Docker, Kubernetes makes use of existing containers and workloads while taking on the complex issues involved in moving to scale. For more information, watch “Kubernetes vs. Docker: It’s Not an Either/Or Question”:

Docker and Kubernetes Work Together

Docker helps to “create” containers, and Kubernetes allows you to “manage” them at runtime. Use Docker for packaging and shipping the app. Employ Kubernetes to deploy and scale your app. Startups or small companies with fewer containers usually can manage them without having to use Kubernetes, but as the companies grow, their infrastructure needs will rise; hence, the number of containers will increase, which can be difficult to manage. This is where Kubernetes comes into play.

When used together, Docker and Kubernetes serve as digital transformation enablers and tools for modern cloud architecture. Using both has become a new norm in the industry for faster application deployments and releases. While building your stack, it is highly recommended to understand the high-level differences between Docker and Kubernetes.

Let containers help to unhitch the mysteries of cloud computing regardless of the cloud journey you choose.

Let’s take a simple scenario of a CI/CD setup using Docker and Kubernetes:

1. The developers’ code is pushed into the Git.
2. The build and test happen with Maven in Jenkins for C.
3. Using Ansible as a deployment tool, we will write Ansible playbooks to deploy on AWS.
4. We will introduce JFrog Artifactory as the repository manager after the build process from Jenkins; the artifacts will be stored in Artifactory.
5. Ansible can communicate with Artifactory, take the artifacts and deploy them onto the Amazon EC2 instance.
6. The SonarQube can help in reviewing the code and will give static code analysis.
7. We then introduce Docker as a containerization tool. Just like the way we did on Amazon EC2, we will deploy the app on Docker container by creating a Docker file and Docker images.
8. Once this above setup is done, we will introduce Kubernetes to create a Kubernetes cluster, and by using Docker images, we will be able to deploy.
9. Finally, we will use Nagios to monitor the infrastructure.

Conclusion

Microservices help companies convert large monolithic applications into smaller components so they can package and deploy them separately without any dependency. Microservices give apps more agility, scalability and resilience — with microservices, apps can be updated, changed and redeployed faster.

That is where tools such as Docker and Kubernetes work together to help companies deploy and scale applications as necessary.

Kubernetes has been spreading like wildfire in the cloud market, and the adoption is increasing every year. Companies including IBM, Amazon, Microsoft, Google and Red Hat offer managed Kubernetes under the containers as a service (CaaS) or platform as a service (PaaS) model. Many global companies are already using Kubernetes in production on a massive scale.

Docker is also a fantastic piece of technology. According to the “RightScale 2019 State of the Cloud Report,” Docker is winning the container segment, with a tremendous year-over-year adoption growth.

Millions of developers are dependent on Docker, downloading 100 million container images a day, and more than 450 organizations have adopted Docker Enterprise Edition, including some of the biggest enterprises in the globe. Many more years to come, Docker and Kubernetes are not going anywhere.