Any typical enterprise-grade application deployed on Kubernetes comprises several API resources that need to be deployed together. For example, the WordPress application, which is one of the example applications available on the Kubernetes GitHub repository, includes:

• a wordpress frontend pod
• a wp-pv-claim persistent volume claim mounted to the frontend pod
• a wordpress-mysql MySQL database pod
• a mysql-pv-claim persistent volume claim mounted to the MySQL database pod
• two persistent volumes: wordpress-pv-1 and wordpress-pv-2 to serve the persistent volume claims
• services for the database and frontend pods

Application (or app) is not a native construct in Kubernetes. However, managing applications is the primary concern of the developers and operations. Application delivery on Kubernetes involves upgrading, downgrading, and customizing the individual API resources. Kubernetes allows you to restrict the spread of your application resources through namespaces such that you can deploy an entire app in a namespace that can be deleted or created. However, a complex application might consist of resources spread across namespaces, and in such cases answering the following questions might be a challenge:

• How many apps are running in a namespace?
• Was the upgrade of all the resources of the app successful?
• Which types of resources are associated with my app?

The kapp Tool

The kapp (Kubernetes App) tool is one of the tools available in the Carvel toolkit. kapp enables users to group a set of resources (resources with the same label) as an application. Furthermore, kapp manages the individual resources of the application so that the users only have to operate at the level of applications through the kapp CLI.

Helm (specifically Helm3) is an alternative to the kapp tool. Just like Helm, kapp can perform a stateful upgrade of the application. However, Kapp does not have templating capabilities like Helm, a capability that is fulfilled by the YTT tool in the Carvel toolkit. By combining kapp with the kapp-controller, you can build neat GitOps workflows, which takes it far beyond the capabilities of Helm.