Kubernetes vs Docker: Key Differences

What is Kubernetes?

Kubernetes (also known as K8s) is a production-grade container orchestration system. It is an open source cluster management system initially developed by three Google employees during the summer of 2014 and grew exponentially and became the first project to get donated to the Cloud Native Computing Foundation(CNCF).

It is basically an open source toolkit for building a fault-tolerant, scalable platform designed to automate and centrally manage containerized applications. With Kubernetes you can manage your containerized application more efficiently.

Kubernetes is a HUGE project with a lot of code and functionalities. The primary responsibility of Kubernetes is container orchestration. That means making sure that all the containers that execute various workloads are scheduled to run physical or virtual machines. The containers must be packed efficiently following the constraints of the deployment environment and the cluster configuration. In addition, Kubernetes must keep an eye on all running containers and replace dead, unresponsive, or otherwise unhealthy containers.

Kubernetes uses Docker to run images and manage containers. Nevertheless, K8s can use other engines, for example, rkt from the CoreOS. The platform itself can be deployed within almost any infrastructure – in the local network, server cluster, data center, any kind of cloud – public (Google Cloud, Microsoft Azure, AWS, etc.), private, hybrid, or even over the combination of these methods. It is noteworthy that Kubernetes supports the automatic placement and replication of containers over a large number of hosts. It  brings a number of features and which can be thought of as:\ 

• As a container platform
• As a microservices platform
• As a portable cloud platform and a lot more.

Kubernetes considers most of the operational needs for application containers. The top 10 reasons why Kubernetes is so popular are as follow:

• Largest Open Source project in the world
• Great Community Support
• Robust Container deployment
• Effective Persistent storage
• Multi-Cloud Support(Hybrid Cloud)
• Container health monitoring
• Compute resource management
• Auto-scaling Feature Support
• Real-world Use cases Available
• High availability by cluster federation

Below is the list of features which Kubernetes provides - 

• Service Discovery and load balancing: Kubernetes has a feature which assigns the containers with their own IP addresses and a unique DNS name, which can be used to balance the load on them.
• Planning & Placement: Placement of the containers on the node is a crucial feature on which makes the decision based on the resources it requires and other restrictions.
• Auto Scaling: Based on the CPU usage, the vertical scaling of applications is automatically triggered using the command line.
• Self Repair: This is a unique feature in the Kubernetes which will restart the container automatically when it fails. If the Node dies, then containers are replaced or re-planned on the other Nodes. You can stop the containers if they don't respond to the health checks.
• Storage Orchestration: This feature of Kubernetes enables the user to mount the network storage system as a local file system.
• Batch execution: Kubernetes manages both batch and CI workloads along with replacing containers that fail.
• Deployments and Automatic Rollbacks: During the configuration changes for the application hosted on the Kubernetes, progressively monitors the health to ensure that it does not terminate all the instances at once, it makes an automatic rollback only in the case of failure.
• Configuration Management and Secrets: All classifies information like keys and passwords are stored under module called Secrets in Kubernetes. These Secrets are used especially while configuring the application without having to reconstruct the image.

What is Docker?

Docker is a lightweight containerization technology that has gained widespread popularity in the cloud and application packaging world. It is an open source framework that automates the deployment of applications in lightweight and portable containers. It uses a number of the Linux kernel’s features such as namespaces, cgroups, AppArmor profiles, and so on, to sandbox processes into configurable virtual environments. Though the concept of container virtualization isn’t new, it has been getting attention lately with bigwigs like Red Hat, Microsoft, VMware, SaltStack, IBM, HP, etc, throwing their weight behind newcomer Docker. Start-ups are betting their fortunes on Docker as well. CoreOS, Drone.io, and Shippable are some of the start-ups that are modeled to provide services based upon Docker. Red Hat has already included it as a primary supported container format for Red Hat Enterprise Linux 7.

Why is Docker popular?

The major factors driving Docker’s popularity are its speed, ease of use and the fact that it is largely free. In performance, it is even said to be comparable with KVM. A container-based approach, in which applications can run in isolation and without relying on a separate operating system, can really save huge amounts of hardware resources. Industry experts have started looking at it as hardware multi-tenancy for applications. Instead of having hundreds of VMs running per server, what if it were possible to have thousands of hardware-isolated applications?

Docker is used to running software packages called "containers". A container is a standardized unit of software that packages up a code and all its dependencies so the application runs quickly and reliably from one computing environment to other. Containers are the “fastest growing cloud-enabling technology”* because they speed the delivery of software and cut the cost of operating it. Writing software is faster. Deploying it is easier — in your data center or your preferred cloud. And running it requires less hardware and support.

Although container technology has existed for decades, Docker makes it work for the enterprise with core features enterprises require in a container platform and best-practice services to ensure success. And containers work on both legacy applications and new development.

Existing, mission-critical applications can be “containerized,” often with little or no change. The result is instant savings in infrastructure, better security, and reduced labor. And new development happens faster because engineers only target a single platform instead of a variety of servers and clouds. Less code to write. Less testing. Faster delivery.

Introduction to Docker swarm.

Docker Swarm is the native clustering and scheduling tool for Docker.  It allows IT, administrators and developers, to establish and manage a cluster of Docker nodes as a single virtual system.  It is written in Go and released for the first time in November 2015 by Docker, Inc.

The cluster management and orchestration features embedded in the Docker Engine are built using swarmkit. Swarmkit is a separate project which implements Docker’s orchestration layer and is used directly within Docker. It is a toolkit for orchestrating distributed systems at any scale. It includes primitives for node discovery, raft-based consensus, task scheduling and more.

Its main benefits are:

• Distributed: SwarmKit uses the Raft Consensus Algorithm in order to coordinate and does not rely on a single point of failure to perform decisions.
• Secure: Node communication and membership within a Swarm are secure out of the box. SwarmKit uses mutual TLS for node authentication, role authorization, and transport encryption, automating both certificate issuance and rotation.
• Simple: SwarmKit is operationally simple and minimizes infrastructure dependencies. It does not need an external database to operate

Current versions of Docker include swarm mode for natively managing a cluster of Docker Engines called a swarm. One can use the Docker CLI to create a swarm, deploy application services to a swarm, and manage swarm behavior. All you need is to initiate it to use the latest features which comes with the Docker Engine. 

Docker Swarm Mode Architecture

Every node in Swarm Mode has a role which can be categorized as a Manager and Worker. Manager node has a responsibility to actually orchestrate the cluster, perform the health-check, running containers serving the API and so on. The worker node just executes the tasks which are actually containers. It cannot decide to schedule the containers on the different machine. It cannot change the desired state. The workers only take work and report back the status. You can enable node promotion or demotion easily through one-liner command.

Managers and Workers use two different communication models. Managers have built-in RAFT system that allows them to share information for new leader election. At one time, the only manager is actually performing the scaling and they use a leader-follower model to figure out which one is supposed to be what. No External K-V store is required as a built-in internal distributed state store is available.

Workers, on the other side, uses GOSSIP network protocol which is quite fast and consistent. Whenever any new container/tasks get generated in the cluster, the gossip is going to broadcast it to all the other containers in a specific overlay network that this new container has started. Please remember that ONLY the containers which are running in the specific overlay network will be communicated and NOT globally. Gossip is optimized for heavy traffic.

How Docker swarm varies with Docker?

Today Docker Platform support 3 variants of Swarm:

• Docker Swarm ( Classic)
• Swarmkit(a foundation for Docker Swarm Mode)
• Docker Swarm Mode

Let us go through each one of them one by one 

Docker Swarm 1.0 was introduced for the first time in Docker Engine 1.9 Release during November 2015. It was a separate GITHUB repo and software which needed to be installed for turning a pool of Docker Engines into a single, virtual Engine.. It was announced as the easiest way to run Docker applications at scale on a cluster. You don’t have to worry about where to put containers, or how they talk to each other – it just handles all that for you.

In 2016 during Dockercon, Docker Inc. announced Docker Swarm Mode for the first time. Swarm Mode came integrated directly into Docker Engine which means you don’t need to install it separately. All you need is to initiate it using `docker swarm init` command. With an optional “Swarm Mode” feature rightly integrated into core Docker Engine, native management of a cluster of Docker Engines, orchestration, decentralized design, service and application deployment, scaling, desired state reconciliation, multi-host networking, service discovery and routing mesh implementation is just a matter of few liner commands.

Said that Docker Swarm mode is fundamentally different from Classic Swarm. The basic difference are listed below:

Let’s talk about Swarmkit a bit.

Swarmkit is a plumbing open source project. It is a toolkit for orchestrating distributed systems at any scale. It includes primitives for node discovery, raft-based consensus, task scheduling and more.

Its main benefits are:

• Distributed: SwarmKit uses the Raft Consensus Algorithm in order to coordinate and does not rely on a single point of failure to perform decisions.
• Secure: Node communication and membership within a Swarm are secure out of the box. SwarmKit uses mutual TLS for node authentication, role authorization, and transport encryption, automating both certificate issuance and rotation.
• Simple: SwarmKit is operationally simple and minimizes infrastructure dependencies. It does not need an external database to operate.

SwarmKit is completely built in Go and leverages a standard project structure to work well with Go tooling. If you want to learn more about Swarmkit, head over to https://github.com/docker/swarmkit/

How Docker can be used with Kubernetes?

From 30,000 feet, Docker and Kubernetes might appear to be similar technologies. They both are an open platform which allows you to run applications within Linux containers. But as you deep-dive little closer, you’ll find that the technologies operate at different layers of the stack, and can even be used together. 

Let’s talk about Docker first-

Docker provides the ability to package and run an application in a loosely isolated environment called a container. At their core, containers are a way of packaging software. The unique feature about container is that when you run a container, you know exactly how it will run - it’s very predictable, repeatable and immutable. You are just left with no unexpected errors when you move it to a new machine, or between environments. All of your application’s code, libraries, and dependencies are packed together in the container as an immutable artifact. You can think of running a container like running a virtual machine, without the overhead of spinning up an entire operating system. 

Docker CLI provides the mechanism for managing the life cycle of the containers. Whereas the docker image defines the build time framework of runtime containers, CLI commands are there to start, stop, restart and perform lifecycle operations on these containers. Today, containers can be orchestrated and can be made to run on multiple hosts. The questions that need to be answered are how these containers are coordinated and scheduled? And how will the application running in these containers communicate with each other? The answer is Kubernetes.

Today, Kubernetes mostly uses Docker to package, instantiate, and run containerized applications. Said that there are various another container runtime available but Docker is the most popular runtime binary used by Kubernetes. Both Kubernetes and Docker build a comprehensive standard for managing the containerized applications intelligently along with providing powerful capabilities. Docker provides a platform for building running and distributing Docker containers. Docker brings up its own clustering tool which can be used for orchestration. But Kubernetes is an orchestration platform for Docker containers which is more extensive than the Docker clustering tool and has the capacity to scale to the production level. Kubernetes is a container orchestration system for Docker containers that is more extensive than Docker Swarm and is meant to coordinate clusters of nodes at scale in production in an efficient manner.  It is a plug and plays architecture for the container orchestration which provides features like high availability among the distributed nodes.

For Example ~ Today it is possible to run Kubernetes under Docker EE 2.0 platform. Docker Enterprise Edition (EE) 2.0 is the only platform that manages and secures applications on Kubernetes in multi-Linux, multi-OS, and multi-cloud customer environments. As a complete platform that integrates and scales with your organization, Docker EE 2.0 gives you the most flexibility and choice over the types of applications supported, orchestrators used, and where it’s deployed. It also enables organizations to operationalize Kubernetes more rapidly with streamlined workflows and helps you deliver safer applications through integrated security solutions.

Difference between Kubernetes and Docker

i) Kubernetes vs Docker

• Set up and installation

• Working in two systems

• Logging and Monitoring

{
  "log-driver": "syslog"
}

• Size

ii) Building and Deploying Containers with Docker

Docker has a capability to builds images automatically by reading the instructions via text file called Dockerfile. It is a simple text file that follows a specific format and instructions set that contains all commands, in order, needed to build a given image. 

A Docker image consists of read-only layers each of which represents a Dockerfile instruction. The layers are stacked and each one is a delta of the changes from the previous layer. For example, below is a simple Dockerfile which 

Consider this Dockerfile:

FROM nginx:latest
COPY wrapper.sh /
COPY html /usr/share/nginx/html
CMD ["./wrapper.sh"]

Each instruction creates one layer:

• FROM creates a layer from the nginx:latest Docker image.
• COPY adds files from your Docker client’s current directory.
• CMD specifies what command to run within the container.

When you run an image and generate a container, you add a new writable layer (the “container layer”) on top of the underlying layers. All changes made to the running container, such as writing new files, modifying existing files, and deleting files, are written to this thin writable container layer.

Building a Docker Image

$docker build -t hellowhale

The above shown `docker build` command builds an image from a Dockerfile and a context. The build context is the set of files at a specified location PATH or URL. The PATH is a directory on your local filesystem. The URL is a Git repository location.

Running the Docker Container

A running Docker Image is called Docker container and all you need is to run the below command to expose port 80 on host machine from a container and get it up and running:

docker run -d -p 80:80 --name hellowhale hellowhale

Tagging the Image

$docker tag hellowhale userid/hellowhale

Pushing the Docker Image to DockerHub

Before you push Docker Image to DockerHub, you need to login to DockerHub first using the below command:

$docker login
$docker push userid/hellowhale

iii) Managing container with Kubernetes

Docker CLI for a standalone system is used to build, ship and run your Docker containers. But if you want to run multiple containers across multiple machines, you need a robust orchestration tool and Kubernetes is the most popular in the list.

Kubernetes is an open source container orchestration platform, allowing large numbers of containers to work together in harmony, reducing operational burden. It helps with things like running containers across many different machines, scaling up or down by adding or removing containers when demand changes, keeping storage consistent with multiple instances of an application, distributing load between the containers and launching new containers on different machines if something fails.

Below are the list of comparative CLI used by Docker Vs Kubernetes to manage containers:

$ docker run -d --restart=always --name nginx-app -p 80:80 nginx

iv) Trends in Docker and Kubernetes

Docker, Inc has around 550+ enterprise customer who uses Docker in a production environment. Few of non-exhaustive list of companies who actively uses Docker are list below:

1. The New York Times
2. PayPal
3. Business Insider
4. Cornell University (Not a company but still can be considered)
5. Splunk
6. The Washington Post
7. Swisscom
8. Alm Brand
9. Assa Abloy
10. Expedia
11. Jabil
12. MetLife
13. Societe Generale
14. GE
15. Groupon
16. Yandex
17. Uber
18. Ebay
19. Shopify
20. Spotify
21. New Relic
22. Yelp

Recently, the Forrester New Wave™: Enterprise Container Platform Software Suites, Q4 2018 report states that Docker leading the pack with a robust container platform well-suited for the enterprise, offering a secure container supply chain from the developer's desktop to production.

Lots of organizations are already using Kubernetes in production—like the ones listed on the Kubernetes case studies page, including eBay, Buffer, Pearson, Box, and Wikimedia. But that is not a complete list. Kubernetes is even more versatile than the official case studies page suggests. Below is a list of companies using it:

List of Kubernetes Users

Microservices Usage

Microservices help developers break up monolithic applications into smaller components. They can move away from all-at-once massive package deployments and break up apps into smaller, individual units that can be deployed separately. Smaller microservices can give apps more scalability, more resiliency and - most importantly - they can be updated, changed and redeployed faster. Some of the biggest public cloud applications run as microservices already.

Containers are a packaging strategy for microservices. Think of them more as process containers than virtual machines. They run as a process inside a shared operating system. A container typically only does one small job - validate a login or return a search result. Docker is a tool that describes those packages in a common format, and helps launch and run them. Linux containers have been around for a while, but their popularity in the public cloud has given rise to an exciting new ecosystem of companies building tools to make them easier to use, cluster and orchestrate them, run them in more places, and manage their life cycles.

Over the last two years, many different types of software vendors - from operating system to IT infrastructure companies - have all joined the container ecosystem. There’s already an industry organization - the open container initiative - guiding the market and making sure everyone plays well together. IBM, HP, Microsoft, VMware, Google, Red Hat, CoreOS - these are just some of the major vendors racing to make containers as easy as possible for developers to use, to share, to protect, and to scale.

The rising demand for multi-cloud environments

With an estimated 85% of today’s enterprise IT organizations employing a multi-cloud strategy, it has become more critical that customers have a ‘single pane of glass’ for managing their entire application portfolio. Most enterprise organizations have a hybrid and multi-cloud strategy. Containers have helped to make applications portable but let us accept the fact that even though containers are portable today but the management of containers is still a nightmare. The reason being –

• Each Cloud is managed under a separate operational model, duplicating efforts
• Different security and access policies across each platform
• Content is hard to distribute and track
• Poor Infrastructure utilization still remains
• The emergence of Cloud-hosted K8s is exacerbating the challenges with managing containerized applications across multiple Clouds

This time Docker introduced new application management capabilities for Docker Enterprise Edition that will allow organizations to federate applications across Docker Enterprise Edition environments deployed on-premises and in the cloud as well as across cloud-hosted Kubernetes. This includes Azure Kubernetes Service (AKS), AWS Elastic Container Service for Kubernetes (EKS), and Google Kubernetes Engine (GKE). The federated application management feature will automate the management and security of container applications on premises and across Kubernetes-based cloud services. It will provide a single management platform to enterprises so that they can centrally control and secure the software supply chain for all the containerized applications.

With this announcement, undoubtedly Docker Enterprise Edition is the only enterprise-ready container platform that can deliver federated application management with a secure supply chain. Not only does Docker give you your choice of Linux distribution or Windows Server, the choice of running in a virtual machine or on bare metal, running traditional or microservices applications with either Swarm or Kubernetes orchestration, it also gives you the flexibility to choose the right cloud for your needs.

Talking about Kubernetes Platform, version 1.3 of container management platform Kubernetes

Introduced cross-cluster federated services with an ability to span workloads across clusters and, by extension, across multiple clouds. This opens up the possibility for workloads that need to draw resources from multiple clouds. This would also mean that large jobs can be split among clouds. Not only this, this introduced an ability to automatically scale services to match demand. 

Increasing support for Docker and Kubernetes

Kubernetes has been enjoying widespread adoption among startups, platform vendors, and enterprises. Companies like Amazon, Google, IBM, Red Hat, and Microsoft offer managed Kubernetes under the Containers as a Service (CaaS) model. The open source ecosystem has dozens of players building various tools covering logging, monitoring, automation, storage, and networking aspects of Kubernetes. System integrators have dedicated practices and offerings based on Kubernetes. Global players like Uber, Bloomberg, Blackrock, BlaBlaCar, The New York Times, Lyft, eBay, Buffer, Squarespace, Ancestry, GolfNow, Goldman Sachs and many others are using Kubernetes in production at massive scale. According to Redmonk, a developer-focused research company, 71 percent of the Fortune 100 use containers and more than 50 percent of Fortune 100 companies use Kubernetes as their container orchestration platform.

Did you know there are 35 certified Kubernetes distribution, 22 certified Kubernetes hosting platform and 50 certified Kubernetes service provider available? Over the last three years, Kubernetes has been adopted by a vibrant, diverse community of providers. The Cloud Native Computing Foundation® (CNCF®), which sustains and integrates open source technologies like Kubernetes® , today announced the availability of the Certified Kubernetes Conformance Program, which ensures Certified Kubernetes™ products deliver consistency and portability, and that 35 Certified Kubernetes Distributions and Platforms are now available. A Certified Kubernetes product guarantees that the complete Kubernetes API functions as specified, so users can rely on a seamless, stable experience.

In the other hand, Docker Enterprise Edition (EE) 2.0 represents a significant leap forward in container platform solutions, delivering the only solution that manages and secures applications on Kubernetes in multi-Linux, multi-OS, and multi-cloud customer environments. One of the most promising features announced with this release includes Kubernetes integration as an optional orchestration solution, running side-by-side with Docker Swarm. Not only this, this release includes Swarm Layer 7 routing improvements, Registry image mirroring, Kubernetes integration to Docker Trusted Registry & Kubernetes integration to Docker EE access controls. With this new release, organizations will be able to deploy applications with either Swarm or fully-conformant Kubernetes while maintaining the consistent developer-to-IT workflow.

Docker EE is more than just a container orchestration solution; it is a full lifecycle management solution for the modernization of traditional applications and microservices across a broad set of infrastructure platforms. It is a Containers-as-a-Service(CaaS) platform for IT that manages and secures diverse applications across disparate infrastructure, both on-premises and in the cloud. Docker EE provides an integrated, tested and certified platform for apps running on enterprise Linux or Windows operating systems and Cloud providers. It is tightly integrated into the underlying infrastructure to provide a native, easy to install experience and an optimized Docker environment.

V) Kubernetes vs Docker swarm

• Installation & Cluster configuration
• GUI
• Scalability
• Auto-Scaling
• Load Balancing
• Rolling Updates & Rollbacks
• Data Volumes
• Logging & Monitoring

Kubernetes is an open-source system for automating deployment, scaling, and management of containerized applications. It was built by Google based on their experience running containers in production using an internal cluster management system called Borg (sometimes referred to as Omega). On the other hand, a Swarm cluster consists of Docker Engine deployed on multiple nodes. Manager nodes perform orchestration and cluster management. Worker nodes receive and execute tasks 

Below is the major list of differences between Docker Swarm & Kubernetes: