kubernetes-cronhpa-controller

Overview

kubernetes-cronhpa-controller is a kubernetes cron horizontal pod autoscaler controller using crontab like scheme. You can use CronHorizontalPodAutoscaler with any kind object defined in kubernetes which support scale subresource(such as Deployment and StatefulSet).

Installation

install CRD

# k8s < v1.22
kubectl apply -f config/crds/autoscaling.alibabacloud.com_cronhorizontalpodautoscalers.yaml
# k8s >=v1.22
kubectl apply -f config/crds/autoscaling.alibabacloud.com_cronhorizontalpodautoscalers.v1.22.yaml

install RBAC settings

# create ClusterRole 
kubectl apply -f config/rbac/rbac_role.yaml

# create ClusterRolebinding and ServiceAccount 
kubectl apply -f config/rbac/rbac_role_binding.yaml

deploy kubernetes-cronhpa-controller

kubectl apply -f config/deploy/deploy.yaml

verify installation

kubectl get deploy kubernetes-cronhpa-controller -n kube-system -o wide 

➜  kubernetes-cronhpa-controller git:(master) ✗ kubectl get deploy kubernetes-cronhpa-controller -n kube-system
NAME                            DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
kubernetes-cronhpa-controller   1         1         1            1           49s

Example

Please try out the examples in the examples folder.

Deploy sample workload and cronhpa

kubectl apply -f examples/deployment_cronhpa.yaml

Check deployment replicas

kubectl get deploy nginx-deployment-basic 

➜  kubernetes-cronhpa-controller git:(master) ✗ kubectl get deploy nginx-deployment-basic
NAME                     DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
nginx-deployment-basic   2         2         2            2           9s

Describe cronhpa status

kubectl describe cronhpa cronhpa-sample 

Name:         cronhpa-sample
Namespace:    default
Labels:       controller-tools.k8s.io=1.0
Annotations:  kubectl.kubernetes.io/last-applied-configuration:
                {"apiVersion":"autoscaling.alibabacloud.com/v1beta1","kind":"CronHorizontalPodAutoscaler","metadata":{"annotations":{},"labels":{"controll...
API Version:  autoscaling.alibabacloud.com/v1beta1
Kind:         CronHorizontalPodAutoscaler
Metadata:
  Creation Timestamp:  2019-04-14T10:42:38Z
  Generation:          1
  Resource Version:    4017247
  Self Link:           /apis/autoscaling.alibabacloud.com/v1beta1/namespaces/default/cronhorizontalpodautoscalers/cronhpa-sample
  UID:                 05e41c95-5ea2-11e9-8ce6-00163e12e274
Spec:
  Exclude Dates:  <nil>
  Jobs:
    Name:         scale-down
    Run Once:     false
    Schedule:     30 */1 * * * *
    Target Size:  1
    Name:         scale-up
    Run Once:     false
    Schedule:     0 */1 * * * *
    Target Size:  3
  Scale Target Ref:
    API Version:  apps/v1beta2
    Kind:         Deployment
    Name:         nginx-deployment-basic
Status:
  Conditions:
    Job Id:           38e79271-9a42-4131-9acd-1f5bfab38802
    Last Probe Time:  2019-04-14T10:43:02Z
    Message:
    Name:             scale-down
    Run Once:         false
    Schedule:         30 */1 * * * *
    State:            Submitted
    Job Id:           a7db95b6-396a-4753-91d5-23c2e73819ac
    Last Probe Time:  2019-04-14T10:43:02Z
    Message:
    Name:             scale-up
    Run Once:         false
    Schedule:         0 */1 * * * *
    State:            Submitted
  Exclude Dates:      <nil>
  Scale Target Ref:
    API Version:  apps/v1beta2
    Kind:         Deployment
    Name:         nginx-deployment-basic
Events:               <none>

if the State of cronhpa job is Succeed that means the last execution is successful. Submitted means the cronhpa job is submitted to the cron engine but haven't be executed so far. Wait for 30s seconds and check the status.

➜  kubernetes-cronhpa-controller git:(master) kubectl describe cronhpa cronhpa-sample
Name:         cronhpa-sample
Namespace:    default
Labels:       controller-tools.k8s.io=1.0
Annotations:  <none>
API Version:  autoscaling.alibabacloud.com/v1beta1
Kind:         CronHorizontalPodAutoscaler
Metadata:
  Creation Timestamp:  2019-11-01T12:49:57Z
  Generation:          1
  Resource Version:    47812775
  Self Link:           /apis/autoscaling.alibabacloud.com/v1beta1/namespaces/default/cronhorizontalpodautoscalers/cronhpa-sample
  UID:                 1bbbab8a-fca6-11e9-bb47-00163e12ab74
Spec:
  Exclude Dates:  <nil>
  Jobs:
    Name:         scale-down
    Run Once:     false
    Schedule:     30 */1 * * * *
    Target Size:  2
    Name:         scale-up
    Run Once:     false
    Schedule:     0 */1 * * * *
    Target Size:  3
  Scale Target Ref:
    API Version:  apps/v1beta2
    Kind:         Deployment
    Name:         nginx-deployment-basic2
Status:
  Conditions:
    Job Id:           157260b9-489c-4a12-ad5c-f544386f0243
    Last Probe Time:  2019-11-05T03:47:30Z
    Message:          cron hpa job scale-down executed successfully. current replicas:3, desired replicas:2
    Name:             scale-down
    Run Once:         false
    Schedule:         30 */1 * * * *
    State:            Succeed
    Job Id:           5bab7b8c-158a-469c-a68c-a4657486e2a5
    Last Probe Time:  2019-11-05T03:48:00Z
    Message:          cron hpa job scale-up executed successfully. current replicas:2, desired replicas:3
    Name:             scale-up
    Run Once:         false
    Schedule:         0 */1 * * * *
    State:            Succeed
  Exclude Dates:      <nil>
  Scale Target Ref:
    API Version:  apps/v1beta2
    Kind:         Deployment
    Name:         nginx-deployment-basic
Events:
  Type    Reason   Age                     From                            Message
  ----    ------   ----                    ----                            -------
  Normal  Succeed  42m (x5165 over 3d14h)  cron-horizontal-pod-autoscaler  cron hpa job scale-down executed successfully. current replicas:3, desired replicas:1
  Normal  Succeed  30m                     cron-horizontal-pod-autoscaler  cron hpa job scale-up executed successfully. current replicas:1, desired replicas:3
  Normal  Succeed  17m (x13 over 29m)      cron-horizontal-pod-autoscaler  cron hpa job scale-up executed successfully. current replicas:2, desired replicas:3
  Normal  Succeed  4m59s (x26 over 29m)    cron-horizontal-pod-autoscaler  cron hpa job scale-down executed successfully. current replicas:3, desired replicas:2

🍻Cheers! It works.

Implementation Details

The following is an example of a CronHorizontalPodAutoscaler.

apiVersion: autoscaling.alibabacloud.com/v1beta1
kind: CronHorizontalPodAutoscaler
metadata:
  labels:
    controller-tools.k8s.io: "1.0"
  name: cronhpa-sample
  namespace: default 
spec:
   scaleTargetRef:
      apiVersion: apps/v1beta2
      kind: Deployment
      name: nginx-deployment-basic
   jobs:
   - name: "scale-down"
     schedule: "30 */1 * * * *"
     targetSize: 1
   - name: "scale-up"
     schedule: "0 */1 * * * *"
     targetSize: 3

The scaleTargetRef is the field to specify workload to scale. If the workload supports scale subresource(such as Deployment and StatefulSet), CronHorizontalPodAutoscaler should work well. CronHorizontalPodAutoscaler support multi cronhpa job in one spec.

The cronhpa job spec need three fields:

name
name should be unique in one cronhpa spec. You can distinguish different job execution status by job name.

schedule
The scheme of schedule is similar with crontab. kubernetes-cronhpa-controller use an enhanced cron golang lib （go-cron） which support more expressive rules.

The cron expression format is as described below:


  Field name   | Mandatory? | Allowed values  | Allowed special characters
  ----------   | ---------- | --------------  | --------------------------
  Seconds      | Yes        | 0-59            | * / , -
  Minutes      | Yes        | 0-59            | * / , -
  Hours        | Yes        | 0-23            | * / , -
  Day of month | Yes        | 1-31            | * / , - ?
  Month        | Yes        | 1-12 or JAN-DEC | * / , -
  Day of week  | Yes        | 0-6 or SUN-SAT  | * / , - ?

Asterisk ( * )

The asterisk indicates that the cron expression will match for all values of the field; e.g., using an asterisk in the 5th field (month) would indicate every month.

Slash ( / )

Slashes are used to describe increments of ranges. For example 3-59/15 in the 1st field (minutes) would indicate the 3rd minute of the hour and every 15 minutes thereafter. The form "*/..." is equivalent to the form "first-last/...", that is, an increment over the largest possible range of the field. The form "N/..." is accepted as meaning "N-MAX/...", that is, starting at N, use the increment until the end of that specific range. It does not wrap around.

Comma ( , )

Commas are used to separate items of a list. For example, using "MON,WED,FRI" in the 5th field (day of week) would mean Mondays, Wednesdays and Fridays.

Hyphen ( - )

Hyphens are used to define ranges. For example, 9-17 would indicate every hour between 9am and 5pm inclusive.

Question mark ( ? )

Question mark may be used instead of '*' for leaving either day-of-month or day-of-week blank.

Predefined schedules

You may use one of several pre-defined schedules in place of a cron expression.

Entry	Description	Equivalent To
@yearly (or @annually)	Run once a year, midnight, Jan. 1st	0 0 1 1 *
@monthly	Run once a month, midnight, first of month	0 0 1 * *
@weekly	Run once a week, midnight between Sat/Sun	0 0 * * 0
@daily (or @midnight)	Run once a day, midnight	0 0 * * *
@hourly	Run once an hour, beginning of hour	0 * * * *
Intervals
You may also schedule a job to execute at fixed intervals, starting at the time it's added or cron is run. This is supported by formatting the cron spec like this:

@every where "duration" is a string accepted by time.ParseDuration (http://golang.org/pkg/time/#ParseDuration).

For example, "@every 1h30m10s" would indicate a schedule that activates after 1 hour, 30 minutes, 10 seconds, and then every interval after that.

Note: The interval does not take the job runtime into account. For example, if a job takes 3 minutes to run, and it is scheduled to run every 5 minutes, it will have only 2 minutes of idle time between each run.

more schedule scheme please check this doc.

Specific Date (@date)

You may use the specific date to schedule a job for scaling the workloads. It is useful when you want to do a daily promotion.

Entry	Description	Equivalent To
@date 2020-10-27 21:54:00	Run once when the date reach	0 54 21 27 10 *

targetSize
TargetSize is the size you desired to scale when the scheduled time arrive.
runOnce
if runOnce is true then the job will only run and exit after the first execution.
excludeDates
excludeDates is a dates array. The job will skip the execution when the dates is matched. The minimum unit is day. If you want to skip the date(November 15th), You can specific the excludeDates like below.
```
  excludeDates:
  - "* * * 15 11 *"
```

Metrics and Monitoring

kubernetes-cronhpa-controller export metrics through prometheus metrics format. Here are core metrics list.

# HELP kube_expired_jobs_in_cron_engine_total Expired jobs in queue of Cron Engine
# TYPE kube_expired_jobs_in_cron_engine_total gauge
kube_expired_jobs_in_cron_engine_total 0

# HELP kube_failed_jobs_in_cron_engine_total Failed jobs in queue of Cron Engine
# TYPE kube_failed_jobs_in_cron_engine_total gauge
kube_failed_jobs_in_cron_engine_total 0

HELP kube_jobs_in_cron_engine_total Jobs in queue of Cron Engine
# TYPE kube_jobs_in_cron_engine_total gauge
kube_jobs_in_cron_engine_total 2

# HELP kube_submitted_jobs_in_cron_engine_total Submitted jobs in queue of Cron Engine
# TYPE kube_submitted_jobs_in_cron_engine_total gauge
kube_submitted_jobs_in_cron_engine_total 0

# HELP kube_successful_jobs_in_cron_engine_total Successful jobs in queue of Cron Engine
# TYPE kube_successful_jobs_in_cron_engine_total gauge
kube_successful_jobs_in_cron_engine_total 2

In most of kubernetes cluster.

kube_jobs_in_cron_engine_total = kube_failed_jobs_in_cron_engine_total + kube_submitted_jobs_in_cron_engine_total + kube_successful_jobs_in_cron_engine_total.

Expired jobs are in unique state when cron engine have exceptions. So kube_failed_jobs_in_cron_engine_total and kube_expired_jobs_in_cron_engine_total are two key metrics to monitor.

Common Question

Could kubernetes-cronhpa-controller and HPA work together?
Yes and no is the answer. kubernetes-cronhpa-controller can work together with hpa. But if the desired replicas is independent. So when the HPA min replicas reached kubernetes-cronhpa-controller will ignore the replicas and scale down and later the HPA controller will scale it up.

Contributing

Please check CONTRIBUTING.md

License

This software is released under the Apache 2.0 license.

AliyunContainerService/kubernetes-cronhpa-controller

AliyunContainerService

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