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

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:

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:

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:

project/api/v2/cronjob_types.go

Apache License

Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

Since we’re in a v2 package, controller-gen will assume this is for the v2 version automatically. We could override that with the +versionName marker.

package v2

Imports

import (
	batchv1 "k8s.io/api/batch/v1"
	corev1 "k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
)

// EDIT THIS FILE!  THIS IS SCAFFOLDING FOR YOU TO OWN!
// NOTE: json tags are required.  Any new fields you add must have json tags for the fields to be serialized.

We’ll leave our spec largely unchanged, except to change the schedule field to a new type.

// CronJobSpec defines the desired state of CronJob
type CronJobSpec struct {
	// The schedule in Cron format, see https://en.wikipedia.org/wiki/Cron.
	Schedule CronSchedule `json:"schedule"`

The rest of Spec

	// +kubebuilder:validation:Minimum=0

	// Optional deadline in seconds for starting the job if it misses scheduled
	// time for any reason.  Missed jobs executions will be counted as failed ones.
	// +optional
	StartingDeadlineSeconds *int64 `json:"startingDeadlineSeconds,omitempty"`

	// Specifies how to treat concurrent executions of a Job.
	// Valid values are:
	// - "Allow" (default): allows CronJobs to run concurrently;
	// - "Forbid": forbids concurrent runs, skipping next run if previous run hasn't finished yet;
	// - "Replace": cancels currently running job and replaces it with a new one
	// +optional
	ConcurrencyPolicy ConcurrencyPolicy `json:"concurrencyPolicy,omitempty"`

	// This flag tells the controller to suspend subsequent executions, it does
	// not apply to already started executions.  Defaults to false.
	// +optional
	Suspend *bool `json:"suspend,omitempty"`

	// Specifies the job that will be created when executing a CronJob.
	JobTemplate batchv1.JobTemplateSpec `json:"jobTemplate"`

	// +kubebuilder:validation:Minimum=0

	// The number of successful finished jobs to retain.
	// This is a pointer to distinguish between explicit zero and not specified.
	// +optional
	SuccessfulJobsHistoryLimit *int32 `json:"successfulJobsHistoryLimit,omitempty"`

	// +kubebuilder:validation:Minimum=0

	// The number of failed finished jobs to retain.
	// This is a pointer to distinguish between explicit zero and not specified.
	// +optional
	FailedJobsHistoryLimit *int32 `json:"failedJobsHistoryLimit,omitempty"`

Next, we’ll need to define a type to hold our schedule. Based on our proposed YAML above, it’ll have a field for each corresponding Cron “field”.

// describes a Cron schedule.
type CronSchedule struct {
	// specifies the minute during which the job executes.
	// +optional
	Minute *CronField `json:"minute,omitempty"`
	// specifies the hour during which the job executes.
	// +optional
	Hour *CronField `json:"hour,omitempty"`
	// specifies the day of the month during which the job executes.
	// +optional
	DayOfMonth *CronField `json:"dayOfMonth,omitempty"`
	// specifies the month during which the job executes.
	// +optional
	Month *CronField `json:"month,omitempty"`
	// specifies the day of the week during which the job executes.
	// +optional
	DayOfWeek *CronField `json:"dayOfWeek,omitempty"`
}

Finally, we’ll define a wrapper type to represent a field. We could attach additional validation to this field, but for now we’ll just use it for documentation purposes.

// represents a Cron field specifier.
type CronField string

Other Types

All the other types will stay the same as before.

// ConcurrencyPolicy describes how the job will be handled.
// Only one of the following concurrent policies may be specified.
// If none of the following policies is specified, the default one
// is AllowConcurrent.
// +kubebuilder:validation:Enum=Allow;Forbid;Replace
type ConcurrencyPolicy string

const (
	// AllowConcurrent allows CronJobs to run concurrently.
	AllowConcurrent ConcurrencyPolicy = "Allow"

	// ForbidConcurrent forbids concurrent runs, skipping next run if previous
	// hasn't finished yet.
	ForbidConcurrent ConcurrencyPolicy = "Forbid"

	// ReplaceConcurrent cancels currently running job and replaces it with a new one.
	ReplaceConcurrent ConcurrencyPolicy = "Replace"
)

// CronJobStatus defines the observed state of CronJob
type CronJobStatus struct {
	// INSERT ADDITIONAL STATUS FIELD - define observed state of cluster
	// Important: Run "make" to regenerate code after modifying this file

	// A list of pointers to currently running jobs.
	// +optional
	Active []corev1.ObjectReference `json:"active,omitempty"`

	// Information when was the last time the job was successfully scheduled.
	// +optional
	LastScheduleTime *metav1.Time `json:"lastScheduleTime,omitempty"`
}

//+kubebuilder:object:root=true
//+kubebuilder:subresource:status

// CronJob is the Schema for the cronjobs API
type CronJob struct {
	metav1.TypeMeta   `json:",inline"`
	metav1.ObjectMeta `json:"metadata,omitempty"`

	Spec   CronJobSpec   `json:"spec,omitempty"`
	Status CronJobStatus `json:"status,omitempty"`
}

//+kubebuilder:object:root=true

// CronJobList contains a list of CronJob
type CronJobList struct {
	metav1.TypeMeta `json:",inline"`
	metav1.ListMeta `json:"metadata,omitempty"`
	Items           []CronJob `json:"items"`
}

func init() {
	SchemeBuilder.Register(&CronJob{}, &CronJobList{})
}

Storage Versions

project/api/v1/cronjob_types.go

Apache License

Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

package v1

Imports

import (
	batchv1 "k8s.io/api/batch/v1"
	corev1 "k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
)

// EDIT THIS FILE!  THIS IS SCAFFOLDING FOR YOU TO OWN!
// NOTE: json tags are required.  Any new fields you add must have json tags for the fields to be serialized.

old stuff

// CronJobSpec defines the desired state of CronJob
type CronJobSpec struct {
	//+kubebuilder:validation:MinLength=0

	// The schedule in Cron format, see https://en.wikipedia.org/wiki/Cron.
	Schedule string `json:"schedule"`

	//+kubebuilder:validation:Minimum=0

	// Optional deadline in seconds for starting the job if it misses scheduled
	// time for any reason.  Missed jobs executions will be counted as failed ones.
	// +optional
	StartingDeadlineSeconds *int64 `json:"startingDeadlineSeconds,omitempty"`

	// Specifies how to treat concurrent executions of a Job.
	// Valid values are:
	// - "Allow" (default): allows CronJobs to run concurrently;
	// - "Forbid": forbids concurrent runs, skipping next run if previous run hasn't finished yet;
	// - "Replace": cancels currently running job and replaces it with a new one
	// +optional
	ConcurrencyPolicy ConcurrencyPolicy `json:"concurrencyPolicy,omitempty"`

	// This flag tells the controller to suspend subsequent executions, it does
	// not apply to already started executions.  Defaults to false.
	// +optional
	Suspend *bool `json:"suspend,omitempty"`

	// Specifies the job that will be created when executing a CronJob.
	JobTemplate batchv1.JobTemplateSpec `json:"jobTemplate"`

	//+kubebuilder:validation:Minimum=0

	// The number of successful finished jobs to retain.
	// This is a pointer to distinguish between explicit zero and not specified.
	// +optional
	SuccessfulJobsHistoryLimit *int32 `json:"successfulJobsHistoryLimit,omitempty"`

	//+kubebuilder:validation:Minimum=0

	// The number of failed finished jobs to retain.
	// This is a pointer to distinguish between explicit zero and not specified.
	// +optional
	FailedJobsHistoryLimit *int32 `json:"failedJobsHistoryLimit,omitempty"`
}

// ConcurrencyPolicy describes how the job will be handled.
// Only one of the following concurrent policies may be specified.
// If none of the following policies is specified, the default one
// is AllowConcurrent.
// +kubebuilder:validation:Enum=Allow;Forbid;Replace
type ConcurrencyPolicy string

const (
	// AllowConcurrent allows CronJobs to run concurrently.
	AllowConcurrent ConcurrencyPolicy = "Allow"

	// ForbidConcurrent forbids concurrent runs, skipping next run if previous
	// hasn't finished yet.
	ForbidConcurrent ConcurrencyPolicy = "Forbid"

	// ReplaceConcurrent cancels currently running job and replaces it with a new one.
	ReplaceConcurrent ConcurrencyPolicy = "Replace"
)

// CronJobStatus defines the observed state of CronJob
type CronJobStatus struct {
	// INSERT ADDITIONAL STATUS FIELD - define observed state of cluster
	// Important: Run "make" to regenerate code after modifying this file

	// A list of pointers to currently running jobs.
	// +optional
	Active []corev1.ObjectReference `json:"active,omitempty"`

	// Information when was the last time the job was successfully scheduled.
	// +optional
	LastScheduleTime *metav1.Time `json:"lastScheduleTime,omitempty"`
}

Since we’ll have more than one version, we’ll need to mark a storage version. This is the version that the Kubernetes API server uses to store our data. We’ll chose the v1 version for our project.

We’ll use the +kubebuilder:storageversion to do this.

Note that multiple versions may exist in storage if they were written before the storage version changes – changing the storage version only affects how objects are created/updated after the change.

//+kubebuilder:object:root=true
//+kubebuilder:subresource:status
//+kubebuilder:storageversion

// CronJob is the Schema for the cronjobs API
type CronJob struct {
	metav1.TypeMeta   `json:",inline"`
	metav1.ObjectMeta `json:"metadata,omitempty"`

	Spec   CronJobSpec   `json:"spec,omitempty"`
	Status CronJobStatus `json:"status,omitempty"`
}

old stuff

//+kubebuilder:object:root=true

// CronJobList contains a list of CronJob
type CronJobList struct {
	metav1.TypeMeta `json:",inline"`
	metav1.ListMeta `json:"metadata,omitempty"`
	Items           []CronJob `json:"items"`
}

func init() {
	SchemeBuilder.Register(&CronJob{}, &CronJobList{})
}

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