By Engine Yard
If you’re aiming for a microservices-based architecture, you might have heard about Docker and Kubernetes. Docker and Kubernetes are tools you use in the lifecycle of a containerized application.
People often ask, “Which one should I use, Docker or Kubernetes?”
Truthfully, the idea that you have to use one over the other is a big misconception. Docker and Kubernetes are different technologies that go well together to build, deploy, run, and maintain containerized applications.
Let’s learn more about Docker and Kubernetes so you can safely deploy your new application in a highly organized, resource-effective environment.
Docker is an open-source containerization platform used to package and distribute your code and its dependencies into portable containers so you can manage and run it in a different environment.
The container technology itself isn't something new. Linux Containers (LXC) is the original Linux container solution that's been around for decades.
However, containers gained traction when Docker, Inc. released its platform in 2013, and it became so popular that it’s now the default file format for containers.
Containers are often compared to virtual machines (VMs), as both of them are virtualization methods used to create multiple isolated environments within one hardware system.
Virtual machines use a hypervisor to emulate hardware that divides its resources for several guest operating systems, which then runs different applications.
While this is an effective method, it’s also an inefficient one.
As each VM has its own operating system, there are copies of multiple documents within a physical infrastructure. This leads to wasted resources and bulky virtual machines that are hard to move.
In comparison, containerization offers portability and agility to developers, as it provides a virtual OS for your containers instead of virtual hardware like VMs do.
Unlike VMs, containers share host OS, and, usually, bins and libraries. The container itself only needs to save the application and the definitions of its dependencies.
For developers, containers ensure that your application’s behavior isn’t affected by the difference between your development and production environment.
As a containerization platform, Docker is what builds, runs, and manages your containers.
You can quickly deploy Docker containers through the public cloud, a bare metal server, a private data center, or any other infrastructure. This can save you a lot of time and frustration, as there are many variables that can affect your code when it moves between different environments.
So, how do you build a container on Docker?
We start with packaging your code (and its dependencies) into a Docker Image by creating a docker file, which contains instructions needed to build your docker image.
When your docker image is finished, you can share it using Docker Hub, a service to find and share your containers with your team.
You can run and test it locally using Docker Engine to make sure it behaves the same way in production.
Then, once you want to deploy your containers, you can use an orchestration platform to help you operate your containers.
Kubernetes is an open-source container orchestration platform used to manage your containers from a dashboard or command line.
Orchestration systems, such as Kubernetes, Mesos, and Docker Swarm, help you orchestrate containerized applications in an organized environment.
They do this by automating the scheduling, provisioning, security, networking, load-balancing, and scaling for all of your containers.
Initially, Kubernetes was an orchestrator developed by Google, who then donated it to the CNCF (Cloud Native Computing Foundation), a strong open source community backing both Docker and Kubernetes.
To understand how Kubernetes helps with containerization, we need to talk about the components within a Kubernetes cluster: pods and nodes.
Kubernetes groups containers that need to coexist in pods. Before running in Kubernetes, you need to specify the resources required by each pod. These limits are used by the scheduler to decide which nodes to place the pods in.
Nodes are the physical infrastructure where your containers are deployed to. The node works like a control system. There’s a master node and one or more worker node.
The master node is the brain of Kubernetes orchestration. It listens for a command from users to maintain or achieve the desired state. The master then compares the current state with the wanted state and decides what to do to achieve the goal.
Once it’s decided, the master passes the command to the worker node, which will adjust its state accordingly.
This is how Kubernetes orchestrates your containers. If you have a complex distributed system, using Kubernetes can help automate your workload through this system.
So, let’s get back to our main question: which one should you use, Docker or Kubernetes?
The answer is both.
There are several similarities between Docker and Kubernetes, which is probably the reason for the misconception that you need to pick one over the other.
• Both open-source projects are backed by the CNCF.
• Both are used to support containerization and microservice architectures.
• Both can be deployed through a public cloud service or on-premises.
However, they're still two different technologies that complement each other perfectly.
Picking one over the other would be like choosing to eat lasagna instead of garlic bread. Sure, both are still enjoyable on their own. However, together they support each other and become a better system.
As a containerization platform, Docker builds your microservices into containers. It packs your code (plus its dependencies) into a container that you can run from any environment. Using Docker Engine, Docker is also responsible for running the Docker images.
On the other hand, a container orchestration platform like Kubernetes is responsible for managing existing containers and ensuring the application is running smoothly for its end users.
In short, Docker is what you need in the beginning stage of your application lifecycle, where you build and deploy your containers.
Then, Kubernetes is what takes care of the rest of your application life cycle, including running, managing, and maintaining your containers.
Given that they’re platforms that support each other, it doesn’t make sense to pick one over the other.
A more appropriate comparison would be Kubernetes and Docker Swarm, Docker’s own orchestration management tool.
As the orchestration management that ships with Docker, Docker Swarm is the most tightly integrated platform to use with Docker.
While this is true, Docker and Kubernetes are so often used together that they’re building each technology with integration in mind. So, although transition will be smoother if you use Docker Swarm, using Kubernetes with Docker is just as easy.
The difference between Docker Swarm and Kubernetes lies in the platforms' complexity.
For one, Docker Swarm is designed to run containers on a single node, while Kubernetes forms a cluster of nodes.
More features are included in Kubernetes than Docker Swarm, including auto-scaling, logging, monitoring, and a GUI.
However, it’s harder to set up your containers because of its advanced toolset and configuration, and it’s easy to get overwhelmed if you have no experience with Kubernetes. You can solve this by using Engine Yard which is built on top of Kubernetes and simplifies deployment so you don't have to deal with the complexity.
So, which one should you use?
Both are great options if you need to deploy and manage an application with a multiservice-based architecture.
If your application is more complicated and you need powerful tools, Kubernetes is what you should look into.
Now that we know more about Kubernetes and Docker, let’s see what happens if we use them together.
Because your containers are distributed among different nodes, your infrastructure becomes more robust, and your application is highly available for your users.
A distributed system like this is great if you’re aiming for a reliable system that always stays online. Even if some of your nodes are down, your application will stay online supported by other nodes.
Kubernetes adjusts automatically based on the load and traffic received by your application. There’s no need to allocate resources before peak time to make sure your servers can handle the traffic.
If your application needs more power, Kubernetes can easily add more nodes and/or containers to adjust to the demand.
Distributing your code into containers makes it easier to maintain containers individually without worrying about the effect your changes will cause on other containers.
Furthermore, Kubernetes is equipped with a lot of tools to help you manage your containers efficiently and automates some of the management for you.
Docker and Kubernetes are both industry standards. They’re so often used together that both platforms’ companies consider integration with the other during development.
Both companies support each other, and they know they’re a perfect match. Docker for Desktop even comes with its own Kubernetes distribution.
Containers help you isolate and pack your code, while Kubernetes assists you with deployment and orchestration. With all the help you get, it frees up some time that you can use to fix bugs or develop new features.
Docker and Kubernetes are great together. That is, if you don't mind the steep learning curve and added complexity Kubernetes brings to your container deployment.
Although combining Kubernetes and Docker adds many benefits for your application, it's not a complete solution.
There are other tools, plugins, and DevOps practices, such as continuous integration / continuous development (CI/CD), that you must add to optimize your Kubernetes cluster.
Instead of figuring everything out on your own and letting your brain scream in confusion at 2 AM, consider using a tool like Engine Yard to deploy containerized app deployments in minutes without any need for a dedicated team to manage software in-house.