I Hate Cron JobsJ.A. Hourclé - 2015 DC-Baltimore Perl

Workshop

I <3 cron

I </3 cronjobs

Problems:•I have no idea which of these

messages are important.•Routine output looks the exact

same as a critical error•You start to ignore those cronjobs

(like clamAV) that generate messages every day.

Solution:

•If the cron job doesn’t generate output, it won’t trigger an e-mail.

Problem #2:•This assumes that it sends to

STDERR when something goes wrong.

•And that there’s enough context in STDERR to debug the problem

•You’ve just trashed whatever other output may have been useful

Solution #2

•Capture output, only display on error

Solution #2.1

•Capture output, only display on error

Problems #3-5:•Programs that only write to

STDOUT•When the absense of output is the

error.•Trying to find the actual error in

really spammy commands• like rsync

Solution #3:

Solution #3:

Problem #6

•The ‘stuck’ cronjob:• Every hour, for the last week, cron jobs

have been starting but not completing.

Problem #n

•(insert problem here)

Use Case #1•Only report if output on STDERR•Otherwise, supress STDOUT•(default)• disable with --ignore-stderr and

--ignore-stdout=0 or --verbose• or use --merge

Use Case #2

•Only report if non-zero status•(default)• --ignore-return to disable reporting of

non-zero status

Use Case #3:

•Report if a process runs too long•--timer=(seconds)

•--timeout=(seconds)

Use Case #4•Prevent new jobs if an older job is

still running•--once• --ignore-once if you don’t want this to

automatically be reported as an error• --name to set the lockfile name

Use Case #5

•Kill old instances if still running before starting the new job

• --once=2

Use Case #6:

•Debugging a cron job• Dump %ENV before running

•--verbose=2 : always generate a message

•--verbose=3 : dumps %ENV

Use Case #7

•Highlight what the error is•--lines=(regex) for ‘known good’

lines.

Use Case #8

•Don’t report if the expected output•--lines=(regex)• optional and repetitive items

•--template=(regex)• must be present

Config file support

•--file=(path_to_YAML)

•any command line args override options set in the file

Doesn’t doeverything

Doesn’t:

•Report before the program ends

Doesn’t:•Generate its own e-mail• So we could change the subject line on

success or failure• see App::CronJob

• or change the recipient list based on sucess/fail,or specific error states.

Doesn’t:

•Track success/failrate• only report (x) failures in a row• or (y) failures per (time)

Doesn’t:

•Limit resources• see Process::Govern

Helper script

Problem:Not released

Solar Dynamics Observatory (SDO)Atmospheric Imaging Assembly (AIA)

171Ångstrom ; 2010/07/08 17:45:48UT ; 2x2 binned