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https://github.com/SocialEngine/rancher-cron

A service that can start containers on a defined schedule.
https://github.com/SocialEngine/rancher-cron

cron-expression golang rancher

Last synced: 3 months ago
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A service that can start containers on a defined schedule.

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README 

        
Rancher Cron Service

========

[![Docker Pulls](https://img.shields.io/docker/pulls/socialengine/rancher-cron.svg)](https://hub.docker.com/r/socialengine/rancher-cron/)

[![Go Report Card](https://goreportcard.com/badge/github.com/socialengine/rancher-cron)](https://goreportcard.com/report/github.com/socialengine/rancher-cron)



This service is used to start containers on a specified schedule and 

uses [robfig/cron](https://github.com/robfig/cron) cron package.



When this service is running on Rancher, it will poll [Rancher Metadata](http://docs.rancher.com/rancher/latest/en/rancher-services/metadata-service/)

for all stacks in an environment to find services that 

have `com.socialengine.rancher-cron.schedule` label set to 

valid cron expression format (see below).



It will automatically update itself with any new and removed services 

every 30 seconds.



Once it finds a container with `com.socialengine.rancher-cron.schedule` 

label, it will start that container on schedule specified by the value 

of that label.



You should not have _Auto Restart_ turned on and have scale of 1 for 

services you wish to run as a cron container.



## Running on Rancher



Use following `docker-compose.yml`

```yml

rancher-cron:

  labels:

    io.rancher.container.create_agent: 'true'

    io.rancher.container.agent.role: environment

  image: socialengine/rancher-cron:0.2.0

```



It is important to include both labels as Rancher will set `CATTLE_URL`, 

`CATTLE_ACCESS_KEY`, and `CATTLE_SECRET_KEY`. If you want a bit more control,

feel free to set those manually.



### Debugging



If something is not working as you expect, you can enable debug output by modifying

the command to `rancher-cron -debug`. This is also helpful for submitting issues.



## 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 not case sensitive.  "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 

```

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!**



## Building



This project uses `govendor` for managing vendor dependancies, so first, please run `govendor sync` to 

install external packages.



### Makefile



Run `make build` to create a new executable.



Run `VERSION=dev make package` to create a new executable and package it into a docker image (which you can then 

test in rancher), it will be named `socialengine/rancher-cron:dev`. This assumes same docker daemon rancher has 

access to.