Until now, our examples were focused on quick and imperative commands by using kubectl <command> i.e. to create deployments and services running on a one-node cluster with minikube. This is convenient for something quick, but does not easily expose the full flexibility of the API. To leverage all the options available via Kubernetes, it is often more effective to manage files that describe the deployment you want.

When using these files, you can use kubectl <command> along with the -f option to specify the file to use. Kubernetes offers a declarative mechanism as well, leveraging the kubectl apply command, which takes in files, reviews the current state, and manages the updates—creating, removing, and so on—as needed, while also keeping a simple audit log of the changes.

It's recommended using the declarative mechanism for anything more complex than running a single process, which will likely be most of your developed services. You may not need the audit trails in development. You probably would in a staging/canary environment or in production, so being familiar and comfortable with them is advantageous to understand them.

Best of all, you can include declarative files in source control, treating them like code. This gives you a consistent means of sharing that application structure among your team members, all of which can use it to provide a consistent environment.

The kubectl apply command has an -R option as well that will recursively descend directories if you are establishing a complex deployment.

In most cases, the YAML format is used. The options and configurations can seem overwhelming. Each resource in Kubernetes has its own format, and some of those formats are changing and under active development. You will notice that some of the APIs and object structures will actively reference either alpha (means it is an early experiment and the data format may change) or beta (means is more solid than purely experimental, and can likely be used in production loads) to indicate the state of maturity of those resources in the project.