Forum Discussion
jonathan_106468
Nimbostratus
NimbostratusExternal Commands thru iRules
Good Morning,
I have a small question on the usage of iRules in GTM.
What we want to achieve is that if an Active Pool Member in GTM is unavailable and GTM tries to switch to the secondary pool, I would like to execute some unix commands on a remote server (being monitored by LTM) and then enable all traffic to be directed to the new pool member.
i.e
Steps
1. GTM sending traffic to 1 pool member (Active Site)
2. GTM detects that Pool member is unavailable
3. GTM starting to try the Standby Pool Member but before it sends traffic it does the following
a. Login to the remote Application server (being monitored by LTM)
b. Run a Unix command on the remote Application server
4. GTM starts sending traffic to the new Pool Member (previously Standby) when the Unix command results in a Success.
According to my research, I was hoping to achieve this by using iRules (using LB_FAILED API)
when LB_FAILED
{
execute Unix command on Remote Server
pool New-Pool (Previously Standby)
}
Do you think this will work?
Which API enables executing remote commands?
Thanks for your help.
Jon
2 Replies
- The_BhattmanHi Jon,
The one thing you can't do is run unix commands through an iRule. However, what you asked can be possible triggered by a custom monitor. The custom script woud monitor the Active Pool members and upon discovering it's unavailable it would log into the remote APP server and run a command and once that is done it would would then officially report back the system is down thereby informing the GTM to fail over.
For example let's say the the GTM is monitoring a vip connected to a pool on the LTM in active site and monitoring a vip on site B (Passive). The LTM is using a custom monitor to check say DNS on the pool members
The script would look something like the following:!/bin/sh these arguments supplied automatically for all external monitors: $1 = IP (nnn.nnn.nnn.nnn notation or hostname) $2 = port (decimal, host byte order) -- not used in this monitor, assumes default port 53 $3 = name to be looked up $4 = string in expected response node_ip=`echo $1 | sed 's/::ffff://'` pidfile="/var/run/`basename $0`.$node_ip..$2.pid" if [ -f $pidfile ] then kill -9 `cat $pidfile` > /dev/null 2>&1 fi echo "$$" > $pidfile dig @${node_ip} ${3} | egrep -v '^$|^;' | grep ${4} > /dev/null 2>&1 For AAAA lookups, use this instead dig @${node_ip} ${3} AAAA| egrep -v '^$|^;' | grep ${4} > /dev/null 2>&1 status=$? if [ $status -eq 0 ] then echo "UP" else here is the code that would remotely log in and execute the unix command fi rm -f $pidfile
What would happen is that if the script failed it would first run the remote command before reporting back to the GTM to fail over to the standby system
Of course this is all theory so you are definitely going to need to test it
I hope this helps
Bhattman 
TechgeeegHi Bhattman,
I have a similar requirement but I need to understand the above code can you pls give some input as to what each line of code is doing here?? I already have a monitor in place and I need to execute the commands on remote machine if the monitor fails.
Regards,
