go-web-app

Go lang application deploying in kubernetes

Go Web Application

This is a simple website written in Golang. It uses the net/http package to serve HTTP requests.

Running the server

To run the server, execute the following command:

go run main.go

The server will start on port 8080. You can access it by navigating to http://localhost:8080/courses in your web browser.

Looks like this

Flux CD Theory

Flux Control Loop and Controllers

• A control loop in Kubernetes is a process that keeps checking the state of your cluster and makes changes to match the desired setup.
• In Flux, controllers are these control loops. They watch the cluster and adjust things to match what you want.

Custom Resource

• A custom resource lets you add new features to Kubernetes.
• Developers can create their own resources using Custom Resource Definitions (CRDs).
• A controller can manage these custom resources, making Kubernetes more flexible.

Operator Pattern

• An Operator is a combination of a custom resource and a controller.
• The custom resource defines what you want, and the controller works to keep it that way.
• Operators often run as pods in your cluster and have the necessary permissions (using ClusterRole and ClusterRoleBinding) to make changes.

Kustomize-controller (in FluxCD)

• The Kustomize-controller is a special operator in FluxCD.
• It looks for a custom resource called Kustomization.
• The Kustomization resource tells it what the desired state of the cluster is (using Kubernetes manifests), and the controller applies those changes.

Key Terms

• Kustomize and kustomization.yml are part of Kubernetes.
• Kustomize-controller and Kustomization custom resource are part of FluxCD.

Kustomize (in Kubernetes)

• Kustomize helps you modify Kubernetes resources without directly changing the original files.
• It’s useful when managing different environments (like development, staging, and production).
• Kustomization.yml is the file Kustomize uses to know what resources to modify.

kustomization.yml

• kustomization.yml is a file that lists which resources Kustomize should work with.
• It can add labels, make changes to certain fields, and create variations for different environments.

Patching in Kustomize and FluxCD

• Patching lets you modify part of an existing setup without redoing everything.
• Two types of patches are commonly used:
	1. JSON Patch: Precise control, changing only specific parts.
	2. Strategic Merge Patch: Kubernetes-friendly, only changes the fields you specify while keeping the rest intact.

Custom Kustomization Resource (in FluxCD)

• The Kustomize-controller in FluxCD watches a custom resource called Kustomization.
• This resource tells the controller where the manifest files are and what needs to be applied to the cluster.
• The controller runs kustomize build to apply these resources and keeps them up-to-date.

Overlays in Kustomize

• Overlays allow you to set up a common base configuration and then apply small changes for different environments.
• This is like an "inheritance" pattern, where most of the setup stays the same, but each environment has its own tweaks.

Simple Summary

• The Kustomize-controller in FluxCD monitors a custom resource called Kustomization.
• This resource points to the manifests that describe what you want in your cluster.
• The controller applies those changes and keeps the cluster in the correct state.
• It works like Kustomize in Kubernetes, allowing you to use patches and overlays to customize resources for different environments.