What's the correct way to extend my crd & its controller without multiversion

[occia]

I'm developing on k8s v1.9.2. I've implemented a crd(let's call it A) and write a controller on it. The controller create deployments, services according to A's some fields. But I get stuck when I try to figure out the controller's future upgrade scheme.

I know in 1.9.2, crd can't have multiple versions, and assuming A's definition likes the following:

type A struct {

    metav1.TypeMeta   `json:",inline"`

    metav1.ObjectMeta `json:"metadata,omitempty"`

    Spec   ASpec   `json:"spec"`
}

type ASpec struct {

        Field1 int32
}

And assuming I have some A's instances running in the cluster, e.g. a1, a2, a3. And a* have their related resources running, e.g. some deployments.

Under my test, when I add a new field to A, recompile & restart my controller, the old running a* have a default value on the new field automatically. But I don't know the backend mechanism.

And the questions are:

1. What's the best way to extend my A, e.g. add new field Field2 or change the Field1 from int32 to string and keep the already running instances (a1, a2, a3...) upgrade to the new A definition smoothly?
   Or, in another way, add/change/delete a field of A, which modifications are acceptable?

2. Can you give me the recommend way to do the future upgrade of A without pulling all already running a* down?

[k8s-ci-robot]

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[shubheksha]

/kind support

[jhorwit2]

@occia Thanks for your questions; however, e are trying to consolidate the channels to which questions for help/support are posted so that we can improve our efficiency in responding to your requests, and to make it easier for you to find answers to frequently asked questions and
how to address common use cases.

Please follow along with the CRD versioning feature ticket to track support of this. You can also read this issue which asked the same question.

/close