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Turbocharge ArgoCD with App of Apps Pattern and Kustomized Helm

Sculpture at Montserrat, Spain. Photo by Dzero Labs.

Well folks, it’s been a few months now since we’ve started on the ArgoCD journey together, and it’s been a wild ride. But we’re not done yet!

If you’ve been following along at home, we’ve gone from setting up ArgoCD and Tekton on Kubernetes, to creating a Kubernetes-native build and release pipeline with Tekton and ArgoCD, to configuring SSO with Active Directory on ArgoCD.

Application Deployments Revisited

So what’s next? Well, we did a simple app deployment with ArgoCD when we did the Tekton + ArgoCD example, which was a good start.

As you may recall, ArgoCD lets us define an Application resource, which is responsible for orchestrating the deployment of an application manifest to the target Kubernetes cluster.

NOTE: When I say “application manifest”, I mean all the YAML definitions that make your microservice run in Kubernetes. For example, Service resource definition and a Deployment resource definition.

The Application definition points to a folder where the manifests are located. Out of the box, ArgoCD supports plain ’ole YAML, Kustomize, Helm, and Jsonnet. (Note: Ksonnet is deprecated as of the time of this writing.)

That’s all well and good, but what about when we have to do something a bit more complicated? Like deploy a bunch of related microservices??

Stick around, because I’ll explain all of that, AND I’ll have a short tutorial at the end that you can try out for yourself.

To follow along in the tutorial, you’ll need to have a Kubernetes cluster with ArgoCD installed. If you need help installing ArgoCD on Kubernetes, DON’T PANIC! Check out my blog post on how to install ArgoCD on an existing Kubernetes cluster on a TLS-enabled Ambassador API Gateway.

The App of Apps Pattern

Since we’re using ArgoCD, we need to create an Application definition for each microservice being deployed. But, since they’re part of an app bundle, it would be nice if we had a way to ArgoCD know that.

NOTE: I refer to “app bundle” as a group of related microservices.

This is where the App of Apps Pattern comes into play. And lucky for us, it’s not rocket science!

Put plainly, the App of Apps Pattern lets us define a root ArgoCD Application (Root App). Rather than point to an application manifest, the Root App points to a folder which contains the Application YAML definition for each microservice that’s point of the app bundle (Child Apps). Each microservice’s Application YAML then points to a directory containing the application manifests.

Let’s consider the Guestbook app, which is based on an example from ArgoCD’s own docs (repo can be found here):

App of Apps Pattern for the Guestbook Application

The diagram above depicts four component microservices which make up the Guestbook App.

The Root App’s definition looks like this:

ArgoCD App of Apps: Sample Root App Definition

Line 14 tells ArgoCD to look into the apps folder of the source repo for the Kubernetes manifests. It so happens that the manifests in that folder are Application definitions for the Child Apps.

Looking at a sample Child App definition, we see something like this:

ArgoCD App of Apps: Sample Child App Definition

In the sample Child App above, when we look at Line 14, it tells ArgoCD to look in the helm-guestbook folder of the source repo for Kubernetes manifests. In this case, it’s the folder where a Helm Chart is defined. The folder could’ve easily contained a Kustomization or plain old Kubernetes YAML files.

One thing I’d also like to point out is Line 11, which states that the destination cluster is dev-cluster. This is different from Line 11 in the Root App definition, whose destination value is in-cluster. This is because the Root app must be deployed to the cluster in which ArgoCD is installed (i.e. in-cluster). The Child App, however, will most likely be deployed to a different cluster — like your DEV, QA, or PROD cluster.

In case you’re wondering how to find the cluster name, simply run this command:

argocd cluster add

The output will show something like this:

CURRENT        NAME         CLUSTER        SERVER
* dev-cluster dev-cluster https://<some_ip>
qa-cluster qa-cluster https://<some_other_ip>

The value from the NAME field in the output above is what you need.

App of Apps Best Practices

It’s worth noting a few best practices around the App of Apps pattern.

1- Create a project for each app bundle

ArgoCD projects provide a logical grouping of applications. They can also be used to:

  • Define trusted Git repos (so you can’t deploy apps pointing to just any old git repo and potentially wreak havoc)
  • Define what types of resources can be created on a cluster (maybe you don’t want someone to be creating RoleBindings willy-nilly?)
  • Define who has access to the project, and therefore, to the Applications in the project.
  • Restrict what clusters you can deploy an app to. Our good ‘ole separation of concerns at work here.

ArgoCD projects are defined using special ArgoCD resource called AppProject.

You can check out a sample ArgoCD AppProject definition below:

The above is a very simple definition and therefore doesn’t take advantage of all of the AppProject goodies listed above, but it gives you a good start.

2- Create environment-specific app bundles and projects

So, we agree that we should create an AppProject per application bundle. Let’s take it a step further and create an AppProject per application bundle per environment. When you think about it, it makes sense. You’ll have to create a separate application bundle definition for each target environment anyway, since you’d need to target different clusters each time you deploy to a different environment.

And yes, you can for sure get fancy and do some templating to create your Application definitions.

3- Keep Application definitions in a separate repo

My personal preference is to have the ArgoCD Application and AppProject definitions in a separate repo from the source code repo.

Why? Because chances are, the team managing application deployment to Kubernetes via ArgoCD is different from the team writing the actual application code.

If you’re still not sure right now, don’t worry. You’ll get a better idea of the setup when we get to the example below.

Kustomized Helm

So, we know that ArgoCD supports Helm and Kustomize, but what about when we want to do something fancier, like Kustomized Helm?

First, why would I want to do Kustomized Helm? Well, Helm is great at some things, and not so great at other things. Same goes for Kustomize.

Helm is great for templating.

Kustomize is great for:

  • Applying common configs to a set of YAML files at once (e.g.labels, namespaces, annotations)
  • Overriding values by applying selective changes to YAML files

So when we talk about Kustomized Helm, it means that we apply a Helm template first, followed by a Kustomize overlay, so you end up with the best of both worlds.

Fortunately, enabling Kustomized Helm on ArgoCD is not hard at all. All we need to do is update the argocd-cm.yml definition by adding an entry for a new plugin, and call it kustomized-helm, like so:

Okay…so what the heck does this do?

We’re telling ArgoCD to run the command on Line 19 if we choose to use the newly-created plugin called kustomized-helm:

helm template ../../helm_base — name-template $ARGOCD_APP_NAME — include-crds > ../../helm_base/all.yml && kustomize build

The above command is doing the following:

1- Render the chart template locally

To do this, we use the helm template command, which, per the above command, saves the output to all.yml.

We’re telling ArgoCD to look for the Chart.yaml in the helm_base folder. This means that our repo must have a helm_base folder in order for this to work.

2- Apply a Kustomization to all.yml

To do this, Kustomize expects a kustomization.yml. In this case, the kustomization.yml must be in the helm_base folder.

Here’s what our sample kustomization.yml would look like:

Now, if you’ve seen ArgoCD’s sample argocd-cm.yml for configuring Kustomized Helm, you’d notice right away that mine differs slightly, in that I “force” you to have this helm_base folder in your repo. The reason why I do this is because I want to make use of Kustomize’s overlays, which is perfect if I want to use different values for different environments to which I’m deploying my app. I basically end up with a file structure like this:

And if I want to define an ArgoCD Application to use the dev overlay, I end up with something like this:

Sample ArgoCD Application definition using Kustomized Helm

Note that on Line 14, we set the path to kustomized_helm/overlays/dev. Referring back to our file structure diagram above, ArgoCD will look in kustomized_helm/overlays/dev for a kustomization.yml file, which looks something like this:

Line 5 refers to our helm_base folder, which is where our base kustomization.yml is located (the one that references the resource all.yml).

So when we run argocd app sync, the process looks something like this:

Kustomized Helm in action

Okay…so now that we know what the heck this mysterious plugin is doing, let’s apply it to our ArgoCD cluster so that it’s available:

kubectl apply -f argocd-cm.yml

Now that we have this plugin defined, how do we use it? To do so, you simply refer to the plugin in your ArgoCD Application spec:

plugin:
name: kustomized-helm

Where kustomized-helm is the name that we gave the plugin that we defined above in Line 13 in argocd-cm.yml.

The full Application YAML looks like this:

An Example

Now that you’ve got a good idea on how the App of Apps Pattern works, let’s put it into practice, shall we?

I’ve basically got the following setup:

1- App of Apps Parent App repo

This repo contains the YAML manifests which define the following for DEV, QA, and PROD environments:

  • The ArgoCD project in which the app will reside
  • The ArgoCD root app
  • The ArgoCD child apps (2048-game and Guestbook)

2- App of Apps Child App: 2048-game repo

Our good ‘ole friend the 2048 game makes a return appearance! Here I’ll be demonstrating what a Kustomized Helm deployment looks like.

3- App of Apps Child App: Guestbook repo

This is based on one of the examples from the ArgoCD example repo, and I just have it here to show what it looks like to deploy two “apps” with the App of Apps pattern. Don’t expect this app to function on its own.

Prerequisites

To run the example below, you’ll need the following:

  • A Kubernetes cluster
  • ArgoCD running on the Kubernetes cluster

If you need help installing ArgoCD on Kubernetes, DON’T PANIC! Check out my blog post on how to install ArgoCD on an existing Kubernetes cluster on a TLS-enabled Ambassador API Gateway.

1- Login to ArgoCD

To login to ArgoCD, replace the values in <…> with your own values, and run the snippet below:

export ARGOCD_USERNAME=<argocd_username>
export ARGOCD_PASSWORD=<argocd_password>
export ARGOCD_SERVER=<argocd_server>
argocd login $ARGOCD_SERVER --username $ARGOCD_USERNAME --password $ARGOCD_PASSWORD

2- Register the repos with ArgoCD

We need to register our repos ArgoCD, so let’s add the 3 repos:

export GIT_TOKEN=<git_personal_access_token>argocd repo add https://github.com/d0-labs/argocd-app-of-apps-parent --username git --password $GIT_TOKENargocd repo add https://github.com/d0-labs/argocd-app-of-apps-child-2048-game --username git --password $GIT_TOKENargocd repo add https://github.com/d0-labs/argocd-app-of-apps-child-guestbook --username git --password $GIT_TOKEN
Registering our repos with ArgoCD

You can now list your repos:

argocd repo list

Which will give you an output that looks something like this:

Sample list of repos registered in ArgoCD

Or if you want to check it out in the GUI, go into the ArgoCD console and click on the gear icon on the left-hand pane, and then click on Repositories:

Newly-registred repositories in ArgoCD

3- Create the Dev Project

Now that we’ve got our repos registered, let’s create our project. Again, we’re creating a project to encapsulate our application. We’re also sticking with our best practice of having a different project per environment.

NOTE: For this tutorial, we’re creating all resources for the DEV environment.

kubectl apply -f argocd/projects/project-dev.yml

Hurray! We’ve created a new project, which you can see by going into the ArgoCD console and clicking on the gear icon on the left-hand pane, and then clicking on Projects:

Your newly-created ArgoCD project

Or, if you’re a CLI-lover like me, you can run:

argocd proj list

Which gives you something like this:

Sample list of ArgoCD projects

4- Create the Root App

We are now ready to create our Root App in ArgoCD. We can do it with kubectl, since, an ArgoCD Application is a (custom) Kubernetes resource:

kubectl apply -f argocd/root-app-dev.yml

As soon as we create our app, we can see it on the ArgoCD console:

Our newly-created Root App

But we’re not done yet. You’ll notice that the status says Missing and OutOfSync.

If we click on that tile, we’ll see this:

Okay…so ArgoCD recognizes the Root App and its two children! It means that it knows that there are Application manifests for the two children, and also even found them, but they haven’t actually been created in Kubernetes. In order to do that, we must run an argocd app sync.

Let’s go ahead and do that now.

5- Sync the Root App and its children

First, let’s sync the Root App:

argocd app sync root-appbundle-app-dev

We immediately see that the child Applications have been created!

But they haven’t been synced. So if we drill into each of these apps, we see this:

2048-game hasn’t been synced
Guestbook app hasn’t been synced

So let’s sync the two child apps with this command:

argocd app sync -l app.kubernetes.io/instance=root-appbundle-app-dev

Note how we don’t even list the individual child apps by name! That’s because we use the special ArgoCD label, app.kubernetes.io/instance, and give it the value root-appbundle-dev, the name of our Root App! That means that if your app consists of 10 apps, you’ll only ever need the above two sync commands (one for the Root App, and one for the Children)!

If everything syncs correctly, you’ll see something like this:

And drilling into each Child App, we see this:

2048-game has been successfully deployed
helm-guestbook app has been successfully deployed

Cleanup

One of the coolest things about using the App of Apps pattern is that when you delete the Root App, by default it deletes the Child Apps and all of their resources, in one fell swoop! That includes namespaces too. So you end up with a very clean delete.

To delete our Root App and all of its children:

argocd app delete root-appbundle-app-dev

More on the argocd app delete command here.

Note that the above command does NOT delete projects and repos. Those need to be done separately.

Deleting our repos from ArgoCD:

argocd repo rm https://github.com/d0-labs/argocd-app-of-apps-parentargocd repo rm https://github.com/d0-labs/argocd-app-of-apps-child-2048-gameargocd repo rm https://github.com/d0-labs/argocd-app-of-apps-child-guestbook

Deleting our project from ArgoCD:

argocd proj delete appbundle-project-dev

NOTES:

You can’t delete a repo unless you delete all apps associated with that repo first.

Similarly, you can’t delete a project until you delete all apps associated with that project first. If your project has associated repos, you must delete those before you can delete the repo.

Gotchas!

It’s worth noting an ArgoCD app deployment gotcha that has caused me a bit of grief in the past. Hopefully this section will save you some hair-pulling.

Sometimes you might notice that when you deploy an application, it will show up as Healthy, but the Sync Status is Unknown. Kind of like this:

Looks good, but it ain’t!

This is not good. It means that something went caca, and most likely your Application definition has an error.

When we click on the tile above to drill in, we see this:

Yup, we definitely have an error!

We definitely see an error (see above, highlighted), because we don’t see the Child Apps. This means that ArgoCD didn’t find the manifests in version control for them. Something is definitely stanky.

We should be seeing something to the diagram below.

What we SHOULD be seeing

You can click on the Error to see what’s up. It reveals this:

Uh…okay…thanks…

You can also see what’s going on by tapping into our good buddy, kubectl describe command for our app, root-appbundle-app-dev:

kubectl describe application -n argocd root-appbundle-app-dev

NOTE: All ArgoCD applications are created in the argocd namespace.

Which gives us output that may look something like this:

In our case, it’s pointing to some sort of authentication issue. Upon closer look, the repo we’re referring to in the spec, d0-argocd-app-of-apps-parent is wrong. We don’t have such a repo registered. We registered argocd-app-of-apps-parent(i.e. no d0- prefix). Sunofa…

Classic Picard facepalm. Image source: CNET.

After your fix the error, I recommend that you just nuke the Application from ArgoCD either via the GUI or argocd app delete, and recreate it again using kubectl.

That’s a wrap!

Okay…we’ve learned a lot today!

We learned that:

  • The App of Apps pattern is great for bundling related applications together.
  • Creating a separate project in ArgoCD for each App of Apps bundle, per target Kubernetes environment (DEV, QA, PROD) is good.
  • Kustomize + Helm make a hell of a tag-team!
  • When you need to nuke your App of Apps app bundle, deleting the Root App in ArgoCD by default does a cascade delete, which cleans up all Child App resources, including namespaces, so you don’t lose your mind doing cleanup.
  • App deletion in ArgoCD does not nukify projects and repos.

And because you’ve put up with yet another long-ass blog post, here’s a picture of a cuddly little silkie chicken. (Silkies, by the way, are the cutest chickens EVER.)

Photo by Paige Cody on Unsplash

Peace, love, and code.

One more thing…

In the spirit of DevOpsyness, it would be cool if we had a cleaner way of creating all of the App of Apps manifests and Kustomized Helm templates discussed here, without having to do it manually, right?

I’m currently working on a follow-up blog post to discuss just that. In the meantime, check out our newly-open-sourced tool that does a bunch of that ArgoCD magic. And stay tuned for the follow-up blog post!

Other stories in my ArgoCD journey

Want to know more on how we got here? Check out the other stories in my ArgoCD journey below!

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