Server: Docker Swarm, Kubernetes, DevOps, Running Apache Cassandra on Kubernetes
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Difference between Docker swarm and Kubernetes
When you are on learning curve of application containerization, there will be a stage when you come across orchestration tools for containers. If you have started your learning with Docker then Docker swarm is the first cluster management tool you must have learnt and then Kubernetes. So its time to compare docker swarm and Kubernetes. In this article, we will quickly see what is docker, what is kubernetes and then comparison between the two.
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Stop Killing Your Cattle: Server Infrastructure Advice
If you've spent enough time at DevOps conferences, you've heard the phrase "pets versus cattle" used to describe server infrastructure. The idea behind this concept is that traditional infrastructure was built by hand without much automation, and therefore, servers were treated more like special pets—you would do anything you could to keep your pet alive, and you knew it by name because you hand-crafted its configuration. As a result, it would take a lot of effort to create a duplicate server if it ever went down. By contrast, modern DevOps concepts encourage creating "cattle", which means that instead of unique, hand-crafted servers, you use automation tools to build your servers so that no individual server is special—they are all just farm animals—and therefore, if a particular server dies, it's no problem, because you can respawn an exact copy with your automation tools in no time.
If you want your infrastructure and your team to scale, there's a lot of wisdom in treating servers more like cattle than pets. Unfortunately, there's also a downside to this approach. Some administrators, particularly those that are more junior-level, have extended the concept of disposable servers to the point that it has affected their troubleshooting process. Since servers are disposable, and sysadmins can spawn a replacement so easily, at the first hint of trouble with a particular server or service, these administrators destroy and replace it in hopes that the replacement won't show the problem. Essentially, this is the "reboot the Windows machine" approach IT teams used in the 1990s (and Linux admins sneered at) only applied to the cloud.
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Running Apache Cassandra on Kubernetes
The Cassandra controller can, of course, perform operations within the Cassandra cluster. For example, want to scale down your Cassandra cluster? Instead of manipulating the StatefulSet to handle this task, the controller will see the CRD change. The node count will change to a lower number (say from six to five). The controller will get that state change, and it will first run a decommission operation on the Cassandra node that will be removed. This ensures that the Cassandra node stops gracefully and redistributes and rebalances the data it holds across the remaining nodes. Once the Cassandra controller sees this has happened successfully, it will modify that StatefulSet definition to allow Kubernetes to decommission that pod. Thus, the Cassandra controller brings needed intelligence to the Kubernetes environment to run Cassandra properly and ensure smoother operations.
As we continue this project and iterate on the Cassandra operator, our goal is to add new components that will continue to expand the tool's features and value. A good example is Cassandra SideCar (shown in the diagram above), which can take responsibility for tasks like backups and repairs. Current and future features of the project can be viewed on GitHub. Our goal for the Cassandra operator is to give devs a powerful, open source option for running Cassandra on Kubernetes with a simplicity and grace that has not yet been all that easy to achieve.
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