topic High Availability Basics in Operating System - HP-UX

High Availability Basics

Dave Cast — Tue, 09 Mar 2010 15:15:17 GMT

I'm thinking of setting up a High Availability Cluster -

Here's a brief description of my situation, I have a front end that serves up ssh connections to customers, I'd like to make it redundant in that I'd like to have a 'failover' server that would take over if that front end failed.

Here's my problem:
There are several cron jobs that run at specific times on this front end, if I were to setup a 'failover' server as part of a High Availability cluster where could I move those jobs too, as it wouldn't be good if they ran on both nodes of the cluster. However if I set them up on just one node, then I have a single point of failure, if that node goes down, those cron jobs will never run.

Re: High Availability Basics

Tingli — Tue, 09 Mar 2010 15:29:08 GMT

Pull those crontab jobs out from cron and run them as processes in loop.

Re: High Availability Basics

Turgay Cavdar — Tue, 09 Mar 2010 15:59:41 GMT

You can write a script which starts/stops the cron jobs.Then you can integrate this script into cluster package control script, so when your package starts it starts the cron for users, when the package stop it deletes the cron for users.

Start script should look like:
/usr/bin/crontab CRON

The file CRON should reside on a file system configured in the package, or you manually replicate it on all nodes. You shouldn't populate your crons with "crontab -e", you should first edit CRON file then use "/usr/bin/crontab CRON" to update crons.

stop script should look like:
/usr/bin/crontab -r

Re: High Availability Basics

Johnson Punniyalingam — Tue, 09 Mar 2010 16:36:11 GMT

As mentioned on the above post,

place all your several cron job under "Cluster pkg" mount points and your place crontab under "pkg.cntl.file" as shown below

function customer_defined_run_cmds
{
# ADD customer defined run commands.
: # do nothing instruction, because a function must contain some command.
/opt/smx/bin/rc/rchDB.pd1 s nv
/usr/sbin/inetd -c
/usr/bin/crontab /opt/smx/bin/cron/abc.cron
test_return 51

Re: High Availability Basics

Rita C Workman — Tue, 09 Mar 2010 18:19:28 GMT

Here's yet another way.

Put all your cronjobs where you do, in cron.
Now put all those same cronjobs on the other servers cron. Now you are going to set them up with one little 'difference'.

A good while back I came across a truly sleek script that Simon Hargrave wrote. What this does is goes out to see if the package is running on "this" node and runs the cron job. If the package isn't running then it does not run the job. Stephen Doud called the script elegant - and it is.

Take a look at this thread.....

http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=886789&admit=109447626+1268158640672+28353475

We use it here on our cluster...

Kindest regards,
Rita