Kubernetes 101

Immutable infrastructure is a practice where servers, once deployed, are never modified.

Containers offer a way to package code, runtime, system tools, system libraries, and configs altogether. This shipment is a lightweight, standalone executable.

Kubernetes provides the ability to run dynamically scaling, containerized applications, and utilizing an API for management.

Kubernetes has become the standard for running containerized applications in the cloud, with the main Cloud Providers (AWS, Azure, GCE, IBM and Oracle) now offering managed Kubernetes services.

K8s objects

• Pod. A group of one or more containers.
• Service. An abstraction that defines a logical set of pods as well as the policy for accessing them.
• Volume. An abstraction that lets us persist data. (containers are ephemeral, data is deleted when container is deleted)
• Namespace. A segment of the cluster dedicated to a certain purpose, for example a certain project
• Node. A Virtual host on which containers/pods are running

K8s controllers

• ReplicaSet (RS). Ensures the desired amount of pod is what’s running.
• Deployment. Offers declarative updates for pods and RS.
• StatefulSet. A workload API object that manages stateful applications, such as databases.
• DaemonSet. Ensures that all or some worker nodes run a copy of a pod.
• Job. Creates one or more pods, runs a certain task(s) to completion, then deletes the pod(s).
  

A docker container image – an executable image containing everything you need to run your application; application code, libraries, a runtime, environment variables and configuration files. At runtime, a container image becomes a container which runs everything that is packaged into that image.

Key k8s features make containerized application scale efficiently:

• Horizontal scaling.Scale your application as needed from command line or UI.
• Automated rollouts and rollbacks.
• Service discovery and load balancing.
• Storage orchestration.
• Secret and configuration management.
• Self-healing.
• Batch execution.
• Automatic binpacking.