My sysAdmin tells me he cannot cluster my java application

Question

Hi
I have a small java application which reads files from a (ftp) directory, validates them and writes them to disk again. This application is being called from a CRON scripts on both servers which runs it every minute. Our hosting company says that on the application needs to be run on both clusterservers at the same time. This causes synch problems when reading the file. 2 applications try to access the same file at the same time.
How can he make the second server start up the application when the first goes down?
Our hostingcompany says that my application is not cluster-aware and that it's impossible to configure the server to start/stop my application.
Can somebody please help me with this?
thanks

Answer 1

there are two ways to approach this (in sun cluster 3.x)
that come to mind.
the first is a quick hack that requires you to use a wrapper
script for your cron job (ie, run this script with cron, and
use this script to start your java prog).
here's the gist of it:
----------------------------->8---------------------------------------------------
#!/bin/sh
# wrapper script for cron jobs on 2-node cluster
# >2 node cluster requires more work
# exit if cluster not active on this node
thisState=`scha_cluster_get -O NODESTATE_LOCAL`
if [ "$thisState" != "UP" ] ; then
exit 0
fi
# find out the node ID of this system
thisNode=`scha_cluster_get -O NODEID_LOCAL`
# if this is not node 1, check to see if node 1 is active
if [ "$thisNode" != 1 ] ; then
node1Name=`scha_cluster_get -O NODENAME_NODEID 1`
node1State=`scha_cluster_get -O NODESTATE_NODE $node1Name`
# if node 1 is active, it will run the program, so
# we can quit
if [ "$node1State" = "UP" ] ; then
exit 0
fi
fi
# at this point, we know this node is active, and is
# either node 1, or is the remaining active node
# in either case, run the program
exec /path/to/my/prog
----------------------------->8---------------------------------------------------
you could even make this a generic wrapper by doing
"exec $@" at the end & supplying the normal program
path & args as arguments to the wrapper script...
the 2nd solution is to essentially write your own "cron":
in other words, a long-running process that simply sleeps
in between trying to run your program (or rewrite your
program to run forever & check the ftp dir occassionally).
then you can use the standard tools to make the program
highly available (scdsbuilder, etc)
hth
p