Containers have become popular thanks to their focus on consistency across platforms from development to production. The rise in interest to containers has in turn brought in higher demands for their deployment and management. The need for better control attracted a number of software options as solutions for container orchestration, which allows for abstraction of individual containers to services with a number of instances or replicas. Two of the major players developing container orchestration are Docker and Kubernetes. In this post, we will take a look at how these two compare.
Kubernetes is an open-source platform for container deployment automation, scaling, and operations across clusters of hosts. The production ready orchestrator draws on Google’s extensive experience of years of working with Linux containers.
Kubernetes aims to provide the components and tools to relieve the burden of running applications in public and private clouds by grouping containers into logical units. Their strengths lie in flexible growth, environment agnostic portability, and easy scaling.
Swarm is the native clustering for Docker. Originally Docker Swarm did not provide much in the sense of container automation, but with the update to Docker Engine 1.12, container orchestration is now built into its core with first party support.
Docker Swarm is designed around four core principles: simple yet powerful with a “just works” user experience, resilient zero single-point-of-failure architecture, secure by default with automatically generated certificates, and backwards compatibility with existing components. The promise of backwards compatibility is especially important to the existing users. Any tools or containers that work with Docker run equally well in Docker Swarm.
Although both orchestrators provide much of the same functionality to one another, there are fundamental differences in between how the two operate. Below are listed some of the most notable points on where these rivals diverge.
Installation and cluster configuration
Takes some work to get up and running
Kubernetes requires a number of manual configurations to tie together its components such as etcd, flannel, and the docker engine. Installation instructions differ from OS to OS and provider to provider. Kubernetes also needs to know much of the cluster configuration in advance like the IP addresses of the nodes, which role each node is going to take, and how many nodes there are in total.
Client, API and YAML definitions are unique to Kubernetes
Kubernetes uses its own client, API and YAML definitions which each differ from that of the standard Docker equivalents. In other words, you cannot use Docker CLI nor Docker Compose to define containers. When switch platforms, commands and YAML definitions will need to be rewritten.
Provides strong guarantees to cluster states at the expense of speed
Kubernetes is in comparison more of an all-in-one framework for distributed systems. Its complexity stems from offering a unified set of APIs and strong guarantees about the cluster state, which slows down container deployment and scaling.
High availability is provided through container replication and service redundancy
Kubernetes and Docker Swarm both ensure high availability of services through replication. The same container is deployed to multiple nodes to provide redundancy and redeployed again if a host running the service goes down making the services self-healing. While either of the container orchestrators can be run on a single server, additional nodes are required for true redundancy.
Enabling load balancing requires manual service configuration
Kubernetes permits much of the load balancing concept when container pods are defined as services. Each service is accessible through a certain set of pods and policies which allow the setup of load balancer pods that can reach the service without worrying about IP addresses.
Container updates and rollbacks
Progressive updates and service health monitoring through the update
Kubernetes handles the update process progressively monitoring service health to retain availability throughout the update process making changes to one pod at the time preventing a service outage.
Volumes shared within pods
Kubernetes volumes are an abstraction to allow containers share data within the same pod. The volumes have an explicit lifetime, they are created and removed together with the pod they are enclosed in. Volumes work in basics just as any other directory, which is accessible to the containers in the same pod. Kubernetes also supports external data volume managers to transfer data between pods.
TLS authentication requires manual configuration for security
Kubernetes commonly uses flannel to accomplish container networking. Containers are joined in a virtual network and announced through etcd. TLS authentication is also possible but requires certificates to be generated and installed manually to all nodes.
Containers can be defined as services that are easily discoverable
Kubernetes relies on etcd and manually defined services for discovery. Containers can announce themselves when started and add the relevant information to the distributed key-value store. An optional cluster addon for DNS server is also supported for easier communication.
Throughout the comparison, it is possible to note how Kubernetes and Docker Swarm fundamentally differ. Swarm focuses on ease of use with integration with Docker core components while Kubernetes remains open and modular. The same difference can be noticed while installing and configuring each of the orchestrators.
- Open source and modular
- Runs well on any operating systems
- Easy service organisation with pods
- Backed by years of expert experience
- Laborious to install and configure
- Incompatible with existing Docker CLI and Compose tools
Docker provides a simple solution that is fast to get started with while Kubernetes aims to support higher demands with higher complexity. For much of the same reasons, Docker has been popular among developers who prefer simplicity and fast deployments. At the same time, Kubernetes is used in production environments by many high profile internet companies running popular services.
Getting started with orchestration
Both Docker Swarm and Kubernetes are capable of running many of the same services but may require slightly different approaches to certain details. Getting to know each of the software can help make the decision when choosing the right tool for you container orchestration. You can find our guide on how to deploy Kubernetes on CoreOS cluster at our support section as well as a quick introduction to Docker Swarm orchestration.
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