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 is a pretty textbook example of a special string format (it is also pretty unreadable unless you are a Unix sysadmin).

Make it a bit more structured. According to the CronJob code, it supports "standard" Cron format.

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

Keeping all that in mind, convert the example above to be slightly more structured:

yaml

schedule:
  minute: */1

Now, at least, there are labels for each of the fields, but you can still easily support all the different syntax for each field.

A new API version is needed for this change. Call it v2:

shell

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

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

Now, copy over the existing types, and make the change:

Storage versions

Now that the types are in place, set up conversion...