Tech Insights
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Kubernetes Versus Docker:
How & What About Containers

As Kubernetes continues to grow in popularity, organizations are asking: “Which is better, Kubernetes or Docker?” This inquiry makes it sound as though they are exchangeable, but that’s incorrect. They are complementary. Docker is a platform for building and handling containers, and Kubernetes (aka k8s) is an orchestrator for container platforms like Docker. Many businesses use them together. A more apt comparison would be Docker Swarm versus Kubernetes (more on this later).


What are the differences between Kubernetes and Docker?

Kubernetes
Docker
What it does Kubernetes is an orchestration system for deploying containers that depends on the concepts of pods and nodes. It’s for the automated, simultaneous deploying and scaling of multiple containers in hybrid and multi-cloud environments. Docker is a platform and a tool for building, distributing and running containers that then can be used in any environment.
Who owns it? Kubernetes was designed at Google but is now open source. The Cloud Native Computing Foundation maintains it. Docker, a company based in Palo Alto, California
When in the application lifecycle do you deploy it? Later, after the app has been packaged in a container—to orchestrate and manage it along with other containers Early on, you build, test and run applications using Docker
How it works Kubernetes first groups together containers running the same application. These containers behave as replicas, and act as load balancers as requests come in. An orchestrator then oversees these groups, making sure that they operate properly as they are deployed into environments. Docker packages up application code along with all of its dependencies, such as libraries, files and necessary configurations, into a single image that can then be deployed in any environment.



What is Kubernetes?

Kubernetes is a portable, open source container platform that eliminates most of the manual processes involved in deploying and scaling containerized applications. Kubernetes comes from the Greek word meaning helmsman or pilot. After designing it, and running it internally for 15 years, Google open sourced the project in 2014 to the Cloud Native Computing Foundation (CNCF), which currently manages it.


Pros

Kubernetes confers many advantages on the organizations that deploy it, enabling teams to:

Take advantage of a huge and growing ecosystem
A gigantic ecosystem of tools (many of them open source, so they’re free) has evolved around Kubernetes, helping to ease its complexity, and making it much easier to deploy.

Improve developer productivity
If integrated well into DevOps processes, teams can achieve significant increases in productivity. K8s ecosystem tools help reduce some of Kubernetes’ complexity, which can shorten release cycles especially for cloud native software, and also improve software quality by streamlining engineering workflows.

Attract the best talent
The top way teams recruit and keep the best developers is to stay on the leading edge of innovation. Kubernetes ranked high among the most-wanted platforms in the Stack Overflow Developer Survey 2019. Given the scarcity of tech talent, this is a win.

Future-proof apps
All major cloud vendors (e.g., Google, Microsoft, Amazon Web Services, and others) support Kubernetes and offer solutions for it. Although other container orchestration solutions exist, they lag Kubernetes in market share, cloud vendor support, and the size and growth rate of their ecosystems.

Scale as needed
Kubernetes can scale to support large, distributed systems.

Make apps more reliable and available
Kubernetes supports high-availability applications. It also enables rolling updates, so software changes can be made without scheduling downtime.

Save money
Depending on the app, Kubernetes can be more cost-efficient to deploy because it requires fewer infrastructure resources. It can scale up applications and their required resources during peak times and scale down infrastructure during less busy times. That means paying less during slow times.


Cons

Complexity hurts team productivity
Kubernetes might be more than teams need, as it can be very complex. For a small development initiative, it may actually impact productivity negatively.

Difficult to learn and use
Precisely because it’s always being improved upon and the ecosystem is constantly growing, k8s can be confusing and the transition to Kubernetes a bit challenging.

Hard to find qualified staff
The average salary for a Kubernetes engineer is nearly USD$150,000 and this skillset can be difficult to find. Teams can train existing staff, but that also requires time and budget investment.




What is Docker?

Docker is an open-source, virtualized containerization platform with a lightweight application engine that solved the long-standing problem of code portability in app development. Teams can build, run and distribute applications in Docker containers to run on Linux, Windows, Macs and almost anywhere else. Although other containerization platforms exist (e.g., BSD Jails, LXD, LXC, and Solaris Zones, among others), Docker is currently the most popular.


Pros

Docker delivers the following benefits to IT organizations:

Allows code to work on any machine
Docker containers eliminate the problem of testing code in one environment, and then not having it work in other environments due to different configurations and settings.

Provides teams with a uniform environment
Everyone uses with the same set up, which allows teams to run scripts and establish processes that ensure entire development teams perform common operations with a simple command. IT can more easily isolate and eliminate environment issues across teams without needing to know how individual machines are set up.

Offers abundant resources
Teams can use a very large number of images for free from the Docker Hub. These images are blueprints to creating containers which can house all services for apps.

Lowers resource usage
Containers are small (tens of megabytes in size) and use less resources than gigabyte virtual machines (VMs), which they replace. A Docker container doesn’t each require its own OS, and all share the same kernel, so servers can host more containers than VMs.


Cons

Increased complexity
An extra layer in the IT process, Docker containers can make both build and deployment more challenging.

Difficulty managing a large number of containers
Tools like Kubernetes help simplify container orchestration.

Concerns with overlooking security and networking challenges
Since there is no full OS, cybersecurity can be overlooked. Hackers have begun targeting systems that are hosted in containers and not secured properly. When trying to limit the access within containers for security, network communications are required, which can be difficult.

Performance problems on non-native environments
Despite the Mac OS being based on UNIX, Docker still requires the Linux kernel (usually Ubuntu) to perform its operations.

Significant learning curve
Learning Docker takes time, even for experienced developers.




What are Kubernetes and Docker, respectively, used for?

Because Kubernetes and Docker both help organizations intelligently manage containerized applications, some confusion has emerged. Kubernetes is now sometimes used as shorthand for an entire container environment based on Docker and Kubernetes.

Docker is a platform and tool for building, distributing and running containers. It offers its own native clustering tool, Docker Swarm, that can be used to orchestrate and schedule containers on machine clusters. But it’s not enough to run containers. You also must be able to:

  • Integrate and orchestrate these modular parts
  • Scale up and scale down based on demand
  • Make them fault tolerant
  • Provide communication across a cluster

Kubernetes is a container orchestration system for Docker containers that coordinates clusters of nodes, at scale, in production to do all those things—integrate, orchestrate, scale, fault tolerance, and communications. It works around the concept of pods, which are scheduling units (and which can include one or more containers) that are distributed among nodes to provide high availability.

Which is better? It’s not really a question that can be answered, as they are used for different tasks and have different advantages.




What about Kubernetes versus Docker Swarm? How do Kubernetes and Docker Swarm compare?

While it’s common to hear questions about Kubernetes versus Docker, a more apt comparison is Kubernetes versus Docker Swarm. Docker Swarm is Docker’s orchestration technology that focuses on clustering for Docker containers—tightly integrated into the Docker ecosystem and using its own API.

A fundamental difference in Kubernetes versus Docker Swarm is that Kubernetes is meant to run across a cluster while Docker Swarm runs on a single node. Kubernetes is more extensive than Docker Swarm in its capabilities.

In a nutshell, this is how Kubernetes compares to Docker Swarm:


Kubernetes
Docker Swarm
Application deployment Applications can be deployed using many microservices and pods. Applications can be used only as microservices in a Docker Swarm cluster.
Graphical user interface (GUI) Kubernetes has GUI dashboards that allow even non-technical users to control clusters. Docker Swarm requires a third-party GUI tool.
Availability Kubernetes offers high availability as it distributes all the pods among the nodes. Docker Swarm offers high availability because all the services can be cloned in the nodes.
Node support Supports up to 5,000 nodes Supports up to 2,000 nodes
Autoscaling Yes No
Container supports Limited to 300,000 containers Limited to 95,000 containers
Load balancing In Kubernetes, pods can be implemented as load balancers inside a cluster. Docker Swarm comes with a DNS element that can be used for distributing incoming requests to services.
Speed of scaling and deployment Kubernetes acts like more of an all-in-one framework when working with distributed systems. It provides strong guarantees of the cluster state and a unified set of APIs. As a result, container scaling and deployment are slower than with a single container platform. Docker Swarm can deploy containers much faster than Kubernetes, providing faster reaction times for scaling on demand.
Container setup Kubernetes offers its own YAML, API, and client definitions. The Docker Swarm API offers the same functionality as Docker, and supports most Docker tools.
Networking Kubernetes’ network model is flat, which allows the pods to communicate with each other. Networks are typically deployed as overlays, and policies are in place to define how the pods interact with one another. When a node joins a Docker Swarm cluster, it creates an overlay network for services for each host in the Docker Swarm.
Logging and monitoring Kubernetes includes built-in tools for managing both logging and monitoring processes. Docker Swarm does not require using any tools for logging and monitoring.


How do Kubernetes and Docker relate to each other?

Again, Kubernetes and Docker work together to provide a holistic way to build, test, run, orchestrate and manage containers.

Another frequently asked question is this: “Can teams use Kubernetes without Docker, and vice versa?” The answer to both questions is “Yes.”

As Kubernetes is a container orchestrator, it needs a container runtime to orchestrate. Kubernetes is most commonly used with Docker, but it also can be used with any container runtime. For example, RunC, cri-o and Containerd are other container runtimes that teams can deploy with Kubernetes. Likewise, Docker can be used without Kubernetes.




Learning Kubernetes versus learning Docker

To learn Docker, teams need to learn about containers, and everything that goes with them. The most difficult aspect is the networking, which is the same networking infrastructure as the host OS. Docker tutorials and self-guided classes are available online from the company.

Kubernetes has more components to learn than Docker. First, teams have to understand container platforms—Docker or others—then second, container orchestration. Kubernetes uses its own YAML, API, and client definitions, and each is different from Docker’s, so must be learned as well.

VMware offers KubeAcademy from VMware (formerly known as Kubernetes Academy Brought to You by VMware). This is a free, product-agnostic Kubernetes and cloud native technology education platform. It provides an accessible, self-paced, learning path to advance skill sets along the Kubernetes journey.

VMware Pivotal Labs is another way to engage with Kubernetes. Pivotal Labs works with teams to build apps, modernize apps and develop platforms while empowering them to learn about Kubernetes and related technologies.




Building on Kubernetes with Tanzu

Ultimately, learning about and making your own Kubernetes versus Docker or Docker Swarm decision requires getting hands-on experience with k8s.


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Building and deploying modern containerized applications is easy with VMware Tanzu. Tanzu offers an enterprise-grade, consistent Kubernetes runtime that you can deploy everywhere: on-premises, public clouds, and edge. It allows you to centralize lifecycle and policy management for all of your Kubernetes clusters, regardless of where they reside. And, when supported by VMware Pivotal Labs, VMware Tanzu enables you to transform your teams and your applications, while simplifying operations across multi-cloud infrastructure.


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