[rancid] Replace commands for specific hosts

[Chris Gauthier]

I would argue that, as in the example below, if a device is changing its bootflash every hour, then you likely have a bug in the operating system.  The ASAs used to do that, but the bug was corrected in a later revision of the OS.

While it may be easy to replace the command being sent to the device, what is the effect on the rancid code downstream?  While I cannot speak authoritatively about the contents of the source code, I do believe there are lines of code that are dependent on specific output strings from previous commands.

"For once you have tasted flight you will walk the earth with your eyes turned skywards, for there you have been and there you will long to return."
-Leonardo da Vinci

From: rancid-discuss-bounces at shrubbery.net [mailto:rancid-discuss-bounces at shrubbery.net] On Behalf Of Valeriy Simonov
Sent: Monday, September 20, 2010 1:38 AM
To: rancid-discuss at shrubbery.net
Subject: [rancid] Replace commands for specific hosts

Hello!

Rancid is great, but there are some situations, when some hosts make too much noise and we can't do anything with that. For example, some Cisco device update their flash too frequent, or some scripts make changes to some ACLs several times a hour. It's too annoying to receive that changes every hour, even if that information has no value. The solution could be simple: just avoid some commands or replace them. I've decided to make a patch for that.

First, we should add some parameters in rancid.conf file:
HOST_REPLACE_CMD=""; export HOST_REPLACE_CMD
HOST_REPLACE_CMD="$HOST_REPLACE_CMD 10.1.1.1, 'show flash', 'show flash | exclude bootflash',"; export HOST_REPLACE_CMD
HOST_REPLACE_CMD="$HOST_REPLACE_CMD 10.2.2.2, 'show flash', 'show flash | exclude bootflash',"; export HOST_REPLACE_CMD
HOST_REPLACE_CMD="$HOST_REPLACE_CMD 10.3.3.3, 'more system:running-config', 'more system:running-config | section exclude standard ist$',"; export HOST_REPLACE_CMD

That parameters are telling script to replace 'show flash' command for hosts 10.1.1.1 and 10.2.2.2 with 'show flash | exclude bootflash' to scrub bootflash info completely, and replace 'more system:running-config' for host 10.3.3.3 with 'more system:running-config | section exclude standard ist$' to exclude standard access-list with name ist from the resulting file. You should use that replacements with certainty that you will not lose some valuable information.

Number of replacements is not limited, just be sure not to skip a comma after last quote in each line (do not place comma after a double quote!).

Next, we should apply a patch to rancid file with the name, ahem, 'rancid':
patchpatchpatchpatchpatchpatchpatchpatchpatchpatch

--- rancid.orig	2010-08-05 11:17:24.000000000 +0600
+++ rancid	2010-09-20 12:50:18.000000000 +0600
@@ -1929,6 +1929,22 @@
 	{'show running-config'		=> 'WriteTerm'},
 	{'write term'			=> 'WriteTerm'},
 );
+# Replace commands if host matches
+$host_replace_cmd = $ENV{HOST_REPLACE_CMD};
+ at commandreplace = ();
+push(@commandreplace, $+) while $host_replace_cmd =~ m{'(.*?)'|(\S+),\s*}g;
+$cr_length = $#commandreplace;
+for($i = 0; $i <= $cr_length; $i = $i + 3) {
+	my $cr_host = $commandreplace[$i];
+	if ($host eq $cr_host) {
+		my $cr_cmdsearch = $commandreplace[$i + 1];
+		my $cr_cmdreplace = $commandreplace[$i + 2];
+		my ($index) = grep { defined $commandtable[$_]{$cr_cmdsearch} } 0..$#commandtable;
+		my $cr_function = $commandtable[$index]{$cr_cmdsearch};
+		splice(@commandtable, $index, 1, {$cr_cmdreplace => $cr_function});
+	}
+}
+
 # Use an array to preserve the order of the commands and a hash for mapping
 # commands to the subroutine and track commands that have been completed.
 @commands = map(keys(%$_), @commandtable);

patchpatchpatchpatchpatchpatchpatchpatchpatchpatch

Check that everything's working fine by running "rancid -d hostname" and checking it's output. I would be glad if this patch or some similar logic will be in the next release of rancid.

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