Changing things up

A fairly common change in a Kubernetes API is to take some data that used to be unstructured or stored in some special string format, and change it to structured data. Our schedule field fits the bill quite nicely for this -- right now, in v1, our schedules look like

yaml

schedule: "*/1 * * * *"

That's a pretty textbook example of a special string format (it's also pretty unreadable unless you're a Unix sysadmin).

Let's make it a bit more structured. According to our CronJob code, we support "standard" Cron format.

In Kubernetes, all versions must be safely round-tripable through each other. This means that if we convert from version 1 to version 2, and then back to version 1, we must not lose information. Thus, any change we make to our API must be compatible with whatever we supported in v1, and also need to make sure anything we add in v2 is supported in v1. In some cases, this means we need to add new fields to v1, but in our case, we won't have to, since we're not adding new functionality.

Keeping all that in mind, let's convert our example above to be slightly more structured:

yaml

schedule:
  minute: */1

Now, at least, we've got labels for each of our fields, but we can still easily support all the different syntax for each field.

We'll need a new API version for this change. Let's call it v2:

shell

kubebuilder create api --group batch --version v2 --kind CronJob

Press y for "Create Resource" and n for "Create Controller".

Now, let's copy over our existing types, and make the change:

Storage Versions

Now that we've got our types in place, we'll need to set up conversion...