Installing Flux

Install Flux on your K8S cluster.

To install flux on our K8S cluster we will need to do the following steps:

Install flux cli on your computer
create a repository in Github where the state of the cluster will be declared in yaml files and stored in that repo
Create a Github PAT (Personal Access Token) that will allow Flux to access the repository
Using Flux cli, running flux bootstrap to install Flux on the cluster

Prerequisites

This lesson assumes you have a kubernetes cluster - server version 1.26 or higher, and on your computer you have kubectl that can communicate with your cluster.
We will not explain those steps, but we do recommend to create a minimal managed cluster in one of the cloud providers (In this course we will use GKE - a GCP managed cluster).

Flux cli

Flux cli is a command line tool that allows you to bootstrap flux on your cluster, and interact with flux running on your cluster. Flux cli can be installed in different ways, but we will install it using homebrew:

brew install fluxcd/tap/flux

For additional installation options check the official documentation.

Make sure that after the installation you can type in the terminal:

flux --version

At the time of writing this article the version is fluxctl version 2.2.2.

Flux cli commands

Flux cli contains various commands that allow you to interact with flux running on your cluster, or help you locally create resources. You can explore the commands by running:

flux --help

Here are some of the main features of the cli:

bootstrap - This command will install flux on your cluster, update flux to a newer version, reinstall extra components if needed.
check - Will verify that your cluster meets the requirements for flux to run.
create - commands that allow you to create flux custom resources (Usually you will use it to create the resources locally with the --export flag and then commit them to the git repository)
reconcile - Means syncing the flux controllers and update k8s cluster state if needed.

Let's start by running the flux check command to verify that our cluster meets the requirements for flux to run:

flux check --pre

Flux sync with git repo

We will soon install flux on our cluster, and flux will create controller pods, those controllers will react to certain flux custom resources. Don't worry about those controllers for now cause we will have lessons about each controller. What is important here is that one of those controller is called source-controller and we can tell this controller to read content from a branches in a git repositories. Now why is this important for us? cause this will basically be our entry point to tell flux, "Watch for flux custom resources in this git repository".
This means that we will give flux permissions to read from a git repository, and then we can create flux Kustomization resource that tells flux to track a certain location in that repository, and then we can create k8s resources in the directory, and then flux will keep that state of our cluster with the resources we create.
During this course we will tell Flux to track branch main in a single git repository, every minute, but we can also tell Flux to track more then one git repo, or multiple branches, for a more distributed system with many teams. In order for Flux to read content from a git repository (in our example we will use github), we will need to create a PAT (Personal Access Token) that will allow Flux to access the repository.

PAT - Personal Access Token

We will configure flux to track on a repository change to know what resources to create, we will have to create a PAT (Personal Access Token) this token will allow flux to access the repository and look at the changes (we can configure a single token to access more then one repo). Our git repo will be hosted on Github, and in Github there are 2 types of PATs, one that has access to all the repositories of the user (classic), and one that has access only to the repositories we allow (fine-grained token). We will create a PAT that has access to only one repository (in our example but on distributed teams configuration we can configure multiple repos), and we will give it the repo scope.
First create a new repository in Github where the state of the k8s cluster will be saved. In this example I created the public repo: ywarezk/academeez-k8s-course.
After the repo is created, let's create a PAT that has access to this repository. Go to Settings/Developer Settings/Personal Access Tokens/Fine-grained token or simply click this link.

Choose a name for the token
Choose the token expiration date - once the token is expired you will have to rotate with a new token
In the repository access allow access only to the repository you created
In the Permissions section, in the Repository permissions select the Contents and change the access to Read and write

Click the Generate token button and you should see a token that start with github_pat_**** copy that token and in the terminal set it as an environment variable:

> export GITHUB_TOKEN=github_pat_****

We are almost ready to bootstrap flux on our cluster, but before we do that let's plan how our git repository will look like.

Multiple clusters

In this course we will work with a single cluster, but in a real world scenario you will have multiple clusters, for example a cluster for staging, a cluster for production, a cluster for development, you might have a cluster for your CI, and more. Flux can manage multiple clusters, not only that but it provides a neat way to share resources between the clusters. Think about all those times when you created a cluster and then installed some ingress controller (in this course we will work with nginx ingress controller) and did over and over again on each cluster, not anymore, now we can construct a neat repository with shared resources in all or some of our clusters.

Our repository will have a /clusters/:name-of-cluster in the clusters folder we will create a folder for each cluster. We will also create an infastructure folder for shared resources between the clusters like nginx ingress controller.

Bootstrap flux

Let's install flux to manage our cluster. We will run the flux bootstrap command and after running that command the k8s state will be stored in a git repository, and every modification to your cluster will be done by pushing changes to the git repository. Remember the source-controller we talked about? Flux will install that controller during the bootstrap, and remember the PAT we created? Flux will store it in a secret (if you place it in the right environment variable), and remember the github repo we created? We will tell Flux to create a resource that source-controller will know to sync with that repo

Run the following command to bootstrap flux on your cluster:

flux bootstrap github \
	--owner=your-username \
	--repository=the-repo-you-opened \
	--branch=main \
    --path=./clusters/staging \
	--personal

Let's examine this command:

using github, owner, repository, branch flux will know the GitRepository resource to create
Using path flux will know where to create the Kustomization resource (we will discuess this in future lesson)
personal let's flux know that we are using personal repo and not organization repo

Based on those flags, flux will create 2 custom resources that flux controllers will examine, and also create all the components that flux needs to run on the cluster. Flux will store all those files in the repository, so after we run this we need to pull the latest changes

clone the repo

Let's clone the repo that we created for flux:

> git clone <url-of-the-repo>

You will notice that flux created a flux-system folder which contains all the resources that flux installed in our cluster. For example in the file gotk-components.yaml you will find this code creating the namespace where flux installed all the controllers:

apiVersion: v1
kind: Namespace
metadata:
  labels:
    app.kubernetes.io/instance: flux-system
    app.kubernetes.io/part-of: flux
    app.kubernetes.io/version: v2.2.2
    pod-security.kubernetes.io/warn: restricted
    pod-security.kubernetes.io/warn-version: latest
  name: flux-system

What did flux install?

When you install flux on your cluster, without specifying and extra flags to the bootstrap command, flux will install the default toolkit which we can examine by running:

> kubectl get all -n flux-system

In the default installation we have the following components:

source-controller
kustomize-controller
helm-controller
notification-controller

We will have lessons about each of those controllers, but for now let's understand that those controllers are watching for custom resources that we will create in the git repository, and will create the resources in the cluster.

Create a Namespace

Let's give flux some work to do. We will create a file in the clusters/staging folder called namespace.yaml with the following content:

apiVersion: v1
kind: Namespace
metadata:
  name:  www

commit and push the changes and wait for a minute and you will see that the namespace is created.

kubectl get namespaces

Summary

Flux is now managing our cluster, what and to achieve that we did the following steps:

Installed flux cli on our computer
Created a repository in Github where the state of the cluster will be declared in yaml files and stored in that repo
Created a Github PAT (Personal Access Token) that will allow Flux to access the repository
Using Flux cli, running flux bootstrap to install Flux on the cluster
Created a namespace in the git repository and saw that flux created that namespace in the cluster

The full source code for this lesson is available here

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