jenkins定时任务
概述
JENKINS作为一款持续集成工具，还是比较简单易用的。
开发过程中，我们主要使用jenkins作为自动化编译工具和自动备份工具。
本文主要介绍一种常见场景的设置方法，即jenkins定时任务的设置方法。
环境
centos：CentOS release 7.0 (Final)或以上版本
Jenkins 2.332.2
定时任务配置
代码库使用本地gitlab管理，在jenkins中原本有一个任务，可以一键备份gitlab数据并归档管理。
该任务需要每周手动点击一次。但还是不够懒。
真的懒应该把这一次点击也省略掉。
打开任务的配置项，Dashboard -> Project Name -> 配置 -> 构建触发器 -> Build periodically，勾选“Build periodically”。
在输入框中输入定时任务配置项。
TZ=Asia/Shanghai
## each saturday morning, run the job
H 0 * * 6
上面的配置代表，在上海时间的每个星期六，0点H分启动1次定时任务，见截图。
配置说明
看了上面的配置方法，是不是觉得很熟悉，和linux系统的crontab定时任务很类似。
官方的使用说明也说了，和cron的规则很类似，但又有小小的不同。
其中最特别的一点，‘H‘代表’hash‘。
比如“H 0 * * 6”的配置表示，任务会在0点的0-59分随机选择分钟数来执行任务，这样的好处就是多个相似任务可以在执行时间上负载均衡，降低任务同时执行的服务器压力。
官方说明如下。
This field follows the syntax of cron (with minor differences). Specifically, each line consists of 5 fields separated by TAB or whitespace:
MINUTE HOUR DOM MONTH DOW
MINUTE Minutes within the hour (0–59)
HOUR The hour of the day (0–23)
DOM The day of the month (1–31)
MONTH The month (1–12)
DOW The day of the week (0–7) where 0 and 7 are Sunday.
To specify multiple values for one field, the following operators are available. In the order of precedence,
* specifies all valid values
M-N specifies a range of values
M-N/X or */X steps by intervals of X through the specified range or whole valid range
A,B,...,Z enumerates multiple values
To allow periodically scheduled tasks to produce even load on the system, the symbol H (for “hash”) should be used wherever possible. For example, using 0 0 * * * for a dozen daily jobs will cause a large spike at midnight. In contrast, using H H * * * would still execute each job once a day, but not all at the same time, better using limited resources.
The H symbol can be used with a range. For example, H H(0-7) * * * means some time between 12:00 AM (midnight) to 7:59 AM. You can also use step intervals with H, with or without ranges.
The H symbol can be thought of as a random value over a range, but it actually is a hash of the job name, not a random function, so that the value remains stable for any given project.
Beware that for the day of month field, short cycles such as */3 or H/3 will not work consistently near the end of most months, due to variable month lengths. For example, */3 will run on the 1st, 4th, …31st days of a long month, then again the next day of the next month. Hashes are always chosen in the 1-28 range, so H/3 will produce a gap between runs of between 3 and 6 days at the end of a month. (Longer cycles will also have inconsistent lengths but the effect may be relatively less noticeable.)
Empty lines and lines that start with # will be ignored as comments.
In addition, @yearly, @annually, @monthly, @weekly, @daily, @midnight, and @hourly are supported as convenient aliases. These use the hash system for automatic balancing. For example, @hourly is the same as H * * * * and could mean at any time during the hour. @midnight actually means some time between 12:00 AM and 2:59 AM.
Examples:
# Every fifteen minutes (perhaps at :07, :22, :37, :52):
H/15 * * * *
# Every ten minutes in the first half of every hour (three times, perhaps at :04, :14, :24):
H(0-29)/10 * * * *
# Once every two hours at 45 minutes past the hour starting at 9:45 AM and finishing at 3:45 PM every weekday:
45 9-16/2 * * 1-5
# Once in every two hour slot between 8 AM and 4 PM every weekday (perhaps at 9:38 AM, 11:38 AM, 1:38 PM, 3:38 PM):
H H(8-15)/2 * * 1-5
# Once a day on the 1st and 15th of every month except December:
H H 1,15 1-11 *
Time zone specification
Periodic tasks are normally executed at the scheduled time in the time zone of the Jenkins master JVM (currently Asia/Shanghai). This behavior can optionally be changed by specifying an alternative time zone in the first line of the field. Time zone specification starts with TZ=, followed by the ID of a time zone.
Complete example of a schedule with a time zone specification:
TZ=Europe/London
# This job needs to be run in the morning, London time
H 8 * * *
# Butlers do not have a five o'clock, so we run the job again
H(0-30) 17 * * *
The supported time zones depend on the Java runtime Jenkins is running on. The list of supported time zone IDs on this instance is:
Africa/Abidjan
Africa/Accra
…
总结
Jenkins的功能很强大，在开发中是很好的辅助工具。
空空如常
求真得真
