DNR scripts in a fan-out deployment

I have a fan-out deployment with a DNR script that runs after each connection, therefore script runs once for each micro-deployment.

Is it possible to run it only for one micro-deployment and not others?

Macro-deployment DNR are not suitable, since the script does some
heavy-duty processing of the manifest.

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Adam Stoller

I have a fan-out deployment with a DNR script that runs after each connection, therefore script runs once for each micro-deployment.

Is it possible to run it only for one micro-deployment and not others?

Macro-deployment DNR are not suitable, since the script does some
heavy-duty processing of the manifest.

You didn't specify, but I'm assuming this is a source-side DNR - yes?

I don't believe you can [reliably] do what you want in a fan-out deployment - perhaps I'm just over-tired right now, but the only way I can think to this semi-reliably right now is to have the DNR script take a parameter (the number of legs) and a temporary file name, and each time the script is run it updates a counter in the temporary file - and only if the number is equal to the number of legs (if you're incrementing) or 0 (if you're decrementing) do you continue with the running of the script.

This obviously has some race-condition / file locking issues - so you might need to build in a locking and looping mechanism (be sure to provide a break-out for the loop too - just in case).

Is it elegant? Nope.
Will it work? Perhaps. To borrow a phrase from IBM - "You make the call"

Valentine

I thought about creating a temp file and locking it and run the first script, that got the lock, the rest of the scripts will bail out.

But with that approach I might end up with no scripts being run at all.

Valentine

Here is a dirty solution for now.


use Fcntl qw(:flock);

open SELF, "< $0" or die "Unable to open self";

unless(flock( SELF, LOCK_EX | LOCK_NB)) {
 print "We do not have a lock, bailing out"; 
 exit 0; 
}