Hi, I've raised this issue on this post:
http://lists.gnu.org/archive/html/help-cfengine/2004-07/msg00113.html In order to eliminate the "reversion botch" and keep the environment equal I'm trying to avoid editing files based on current patterns. I always tell cfengine to empty the file and insert needed lines. If current file is exactly the same as the result of the editfile action , cfengine doesn't do anything. Zeev -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Alva Couch Sent: Saturday, November 19, 2005 3:43 AM To: help-cfengine@gnu.org Subject: Re: convergence and undoing changes Mark Burgess wrote: > You are correct however in pointing out that users CAN screw this up > by trying to be too clever, by not thinking convergently. This is what I am getting at. > But that is not the normal state of affairs. My experience is that users are all too cavalier about the way they modify cfagent.conf. I think a specific discipline -- unknown to many users -- is the key. We can either document that discipline or encapsulate it in some kind of transaction engine. I propose to do both. My examples using editfiles are a matter of public record. But the problem can even happen when one utilizes purely convergent actions. Here's a "typical" example of user thinking. - user asserts contents of a file F. Say it is a service startup in /etc/xinetd.d and the intent is to customize some service. - then, some time after F is stable, the user changes the assertion to revert F to its original state. - unbeknownst to the user, some different set of stations are down while F is reverting to the original state. - then, satisfied that the file is reverted, the user takes the reversion assertion out of the script, considering work to be done. - time passes and the unreverted machines come back up. There is no reversion to affect them. So they stay with the new version. - At this point, there are two classes of machines: those with the original version of F and those with the new version. If the new version has a security hole, congratulations, you didn't manage to plug it. The key here is that for reversions to be effective, they must stay in the configuration until it is absolutely sure that all stations have applied them. In a very large network, one is likely never sure, so one can *never* remove the reversions from the config file. This is the principle of observability: Once one manages a thing, one must continue to manage that thing in perpetuity. In my experience this kind of "reversion botch" is very common. -- Dr. Alva L. Couch Associate Professor of Computer Science Associate Professor of Electrical and Computer Engineering Tufts University, 161 College Avenue, Medford, MA 02155 Phone: +1 (617) 627-3674 Web: http://www.cs.tufts.edu/~couch _______________________________________________ Help-cfengine mailing list Help-cfengine@gnu.org http://lists.gnu.org/mailman/listinfo/help-cfengine _______________________________________________ Help-cfengine mailing list Help-cfengine@gnu.org http://lists.gnu.org/mailman/listinfo/help-cfengine
