• Table of Contents

Recap

Recapping from last week's lecture, we discussed the basics of Kubernetes, which is a container orchestration platform used for managing containerized applications. A Kubernetes cluster consists of one or more worker nodes and one master node.

Figure 11.1 Kubernetes cluster

When interacting with Kubernetes, you can use the kubectl command-line tool.

<aside> <img src="/icons/map-pin_gray.svg" alt="/icons/map-pin_gray.svg" width="40px" /> In our lab, we will be using Google Cloud as our Kubernetes environment. Google Cloud Platform (GCP) offers Kubernetes Engine (GKE) as one of its managed Kubernetes services.

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We also discussed the roles of the API server, Replication Controller, and Scheduler in the master node.

• The API server is responsible for exposing Representational State Transfer (REST) APIs to interact with the Kubernetes cluster.
• The replication controller’s job is to ensure that the intended or desired number of pod replicas are running in the cluster at any given time.
• Scheduler is a component that is responsible for placing (scheduling to run) the containers in the cluster nodes.

Introduction to Kubernetes Service

Kubernetes Services provide an abstraction layer that allows client requests to be directed to a related set of pods. So why exactly might we need it? As we covered last week, modern software architecture treats software as a short-term piece of work.

<aside> <img src="/icons/map-pin_gray.svg" alt="/icons/map-pin_gray.svg" width="40px" /> This abstraction layer is defined in Kubernetes YAML configuration files, which we'll cover in more detail as the final main topic of these notes and the course overall.

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In Kubernetes, pods can frequently die or be replaced due to various factors.

• Let's consider a scenario where we have a container for borrowing books.

  

• To handle high traffic and achieve high availability, we can have multiple replicas of the borrowing books container.

  

• Whenever a new port is created, their IP addresses is assigned. After its been deleted, a new IP address is assigned to that port.

  

  This frequent creation and destruction of pods means that their IP addresses are not fixed and can change at any time.

This is where Kubernetes services come into play. A service provides a stable IP address and port number for clients to connect to, regardless of the number of pods providing the service or their IP addresses.

• The Kubernetes service is responsible for directing the request to the appropriate pod that can handle the request.