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lpw-2012
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Oleg Komarov
November 24, 2012
Programming
1
330
lpw-2012
Reliable Cron Jobs in Distributed Environment
Oleg Komarov
November 24, 2012
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Transcript
Reliable Cron Jobs in Distributed Environment Oleg Komarov 2012-11-24 1/26
Presentation available at https://speakerdeck.com/komarov/lpw-2012 http://bit.ly/VLuT6g 2/26
Context 3 independent projects with shared infrastructure • over 30
boxes • over 200 scripts, 30K+ SLOC • packaged in appr. 20 deb-packages 3/26
TL;DR Reliable Cron Jobs in Distributed Environment 4/26
TL;DR Reliable Cron Jobs in Distributed Environment ... are HARD
to get right 4/26
Cron Jobs in a Vacuum • locks • logging and
output • monitoring • profiling 5/26
Logging and Output • log START and FINISH • log
enough details 6/26
Logging and Output • log START and FINISH • log
enough details • use log + STDERR for important things • use MAILTO to catch that output 6/26
Logging and Output • log START and FINISH • log
enough details • use log + STDERR for important things • use MAILTO to catch that output 6/26
Monitoring • be confident that it actually works • it
must not fail when you system fails • have a plan of action 7/26
Monitoring • be confident that it actually works • it
must not fail when you system fails • have a plan of action 7/26
What to monitor • hardware errors • free disk space
• load • crond is alive • age of generated file, queue size, etc. 8/26
Profiling • Does it need 1GB or 10GB? • What
does it take so long to complete? • How many db queries does it run? 9/26
Profiling • Does it need 1GB or 10GB? • What
does it take so long to complete? • How many db queries does it run? Measure and improve 9/26
More to consider • crash-safe • documentation • parallel execution
• resource limits (ulimit/cgroups) 10/26
Deployment Packages 11/26
Deployment Boxes 12/26
Cron Package Just populate my-project-scriptsN.cron.d file 13/26
Cron Package Just populate my-project-scriptsN.cron.d file Don’t write it by
hand, do it automatically 13/26
Cron Package Just populate my-project-scriptsN.cron.d file Don’t write it by
hand, do it automatically Put some METADATA in your scripts 13/26
Metadata =head1 METADATA <crontab> package: scriptsN params: --mod 2 --rem
0 time: */2 * * * * </crontab> <crontab> package: scriptsN params: --mod 2 --rem 1 time: */2 * * * * </crontab> =cut 14/26
Simple Setup As simple as possible: one box per package
15/26
Simple Setup As simple as possible: one box per package
apt-get purge && kill (or wait) && apt-get install 15/26
!%*#$ Back to Earth Network 16/26
With Extra Boxes Now you have some promblems to solve:
• locks • logs • load 17/26
Net::ZooKeeper::Lock Apache ZooKeeperTM is an effort to develop and maintain
an open-source server which enables highly reliable distributed coordination. Net::ZooKeeper::Lock implements distributed locks via ZooKeeper. 18/26
Introducing Switchman https://github.com/komarov/switchman 19/26
Overview 20/26
Configuration Crontabs are installed everywhere, switchman consults with config in
ZooKeeper: { "groups": { "scripts1": "box1", "scripts2": "box1", "scripts3": ["box1", "box2"] } } 21/26
Description switchman --config /how/to/connect/to/zk --group scriptsN -- CMD ARGS 22/26
Description switchman --config /how/to/connect/to/zk --group scriptsN -- CMD ARGS •
checks configuration • acquires a lock • watches configuration for changes • stops execution when it is not allowed anymore 22/26
Description switchman --config /how/to/connect/to/zk --group scriptsN -- CMD ARGS •
checks configuration • acquires a lock • watches configuration for changes • stops execution when it is not allowed anymore Easy to adopt with METADATA 22/26
One Problem Solved • locks • logs • load 23/26
Further Steps See facebook’s Scribe for collecting decentralized logs Resources
reservation and management A good monitoring system 24/26
Thanks! Questions? https://speakerdeck.com/komarov/lpw-2012 http://bit.ly/VLuT6g http://about.me/komarov om 25/26
Bonus Slide Get file age: # in days perl -E
’say -M $ARGV[0]’ /path/to/file # in seconds expr ‘date +%s‘ - ‘date +%s -r /path/to/file‘ Simple local locks: use Pid::File::Flock qw/:auto/; 26/26