kron

README

kron

Usage

First, you need to create a service account for kron:

# account.yaml
apiVersion: v1
kind: ServiceAccount
metadata:
  name: kron

kubectl create -f account.yaml

Then, create a job with labels and annotations for kron:

# job.yaml
apiVersion: batch/v1
kind: Job
metadata:
  name: "sample-job"
  labels:
    kron: true
  annotations:
    schedule: "@every 5m"
spec:
  completions: 0
  template:
    metadata:
      name: "sample-job"
    spec:
      containers:
      - image: alpine:3.4
        name: "sample-job"
        command: ["echo", "$TEST_VAR"]
        env:
        - name: TEST_VAR
          value: ok
      restartPolicy: Never

kubectl create -f job.yaml

Set spec.completions to 0 if you don't want the job to be executed when you create it.

Finally, run the kron service:

apiVersion: v1
kind: Pod
metadata:
  name: kron
spec:
  serviceAccountName: kron
  containers:
  - image: "sabaka/kron"
    name: kron

Scheduling - CRON expression format

A cron expression represents a set of times, using 6 space-separated fields.

	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  | * / , - ?

Note: Month and Day-of-week field values are case insensitive. "SUN", "Sun", and "sun" are equally accepted.

Special Characters

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 0 1 1 *
	@monthly               | Run once a month, midnight, first of month | 0 0 0 1 * *
	@weekly                | Run once a week, midnight on Sunday        | 0 0 0 * * 0
	@daily (or @midnight)  | Run once a day, midnight                   | 0 0 0 * * *
	@hourly                | Run once an hour, beginning of hour        | 0 0 * * * *

Intervals

You may also schedule a job to execute at fixed intervals. This is supported by formatting the cron spec like this:

    @every <duration>

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 every 1 hour, 30 minutes, 10 seconds.

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.

Time zones

All interpretation and scheduling is done in the machine's local time zone (as provided by the Go time package (http://www.golang.org/pkg/time).

Be aware that jobs scheduled during daylight-savings leap-ahead transitions will not be run!

Development

glide install