The Health Probe pattern is about how an application can communicate its health state to Kubernetes. To be fully automatable, a cloud-native application must be highly observable by allowing its state to be inferred so that Kubernetes can detect whether the application is up and whether it is ready to serve requests. These observations influence the lifecycle management of Pods and the way traffic is routed to the application.
The foundation of successful application deployment, management, and coexistence on a shared cloud environment is dependent on identifying and declaring the application resource requirements and runtime dependencies. This Predictable Demands pattern is about how you should declare application requirements, whether they are hard runtime dependencies or resource requirements. Declaring your requirements is essential for Kubernetes to find the right place for your application within the cluster.
The heart of the Declarative Deployment pattern is Kubernetes’ Deployment resource. This abstraction encapsulates the upgrade and rollback processes of a group of containers and makes its execution a repeatable and automated activity.
Containerized applications managed by cloud-native platforms have no control over their lifecycle, and to be good cloud-native citizens, they have to listen to the events emitted by the managing platform and adapt their lifecycles accordingly. The Managed Lifecycle pattern describes how applications can and should react to these lifecycle events.
Foundational patterns describe a number of fundamental principles that containerized applications must comply with in order to become good cloud-native citizens. Adhering to these principles will help ensure your applications are suitable for automation in cloud-native platforms such as Kubernetes.
Automated Placement is the core function of the Kubernetes scheduler for assigning new Pods to nodes satisfying container resource requests and honoring scheduling policies. This pattern describes the principles of Kubernetes’ scheduling algorithm and the way to influence the placement decisions from the outside.
In this introductory chapter, we set the scene for the rest of the book by explaining a few of the core Kubernetes concepts used for designing and implementing container basedcloud-native applications. Understanding these new abstractions, and the related principles and patterns from this book, are key to building distributed applications made automatable by cloud-native platforms. This chapter is not a prerequisite for understanding the patterns described later.Readers familiar with Kubernetes concepts can skip it and jump straight into the pattern category of interest.
