Re: mod_fcgid: different instances of the same program
On Tue, Nov 10, 2009 at 1:47 AM, Danny Sadinoff da...@sadinoff.com wrote: On Tue, Nov 10, 2009 at 12:53 AM, Jeff Trawick traw...@gmail.com wrote: On Mon, Nov 9, 2009 at 5:16 PM, Danny Sadinoff danny.sadin...@gmail.com wrote: 2) Virtual hosts The above item holds true even across virtual hosts. So while it's possible to adjust the FcgidInitialEnv items on a per-vhost basis, this is a recipe for disaster if two vhosts point at the same fcgi executable, because the resulting processes with potentially different Environments will be inserted into the same pool. Once that occurs, we may expect that a server spawned with config defined in vhost A will be parcelled out to vhost B. Where does this occur? Entries in the process table are distinguished by virtual host. (I think the implementation of this check is broken, in that it requires that ServerName is set in the virtual hosts. Are you using a simple test config that doesn't have ServerName set?) My case is not yet simple. I'll get back to you. It turns out that the problem was that I was using mod_fcgid-2.2 Upgrading to mod_fcigd-2.3.4 fixed the problem. I apologize for the noise. Should this item (vhost independence) be added to the upgrade notes section? Are new features in mod_fcgid going to be manifest in the documentation in general? -- Danny Sadinoff da...@sadinoff.com
mod_fcgid: different instances of the same program
Here are two details of mod_fcgid process management that I've just learned after a long debug session and squinting at the mod_fcgid code. 1) symlinks you. It seems that mod_fcgid identifies fcgid programs by inode and device, not by filename. So two fcgid programs invoked by the webserver along different paths will be counted as the same if the two paths are hardlinks or softlinks to each other. 2) Virtual hosts The above item holds true even across virtual hosts. So while it's possible to adjust the FcgidInitialEnv items on a per-vhost basis, this is a recipe for disaster if two vhosts point at the same fcgi executable, because the resulting processes with potentially different Environments will be inserted into the same pool. Once that occurs, we may expect that a server spawned with config defined in vhost A will be parcelled out to vhost B. The Apache httpd 2.3 docs do not address the symlink issue at all, and the virtual host issue only indirectly. http://httpd.apache.org/mod_fcgid/mod/mod_fcgid.html I'd appreciate it if someone could confirm or deny the above. If I'm right, can we add it to the docs? None of it seems obvious to me. Apologies in advance if this is the sort of thing that belongs on the dev list. I'm happy to throw together a doc patch. Thanks in advance P.S. having a lot of trouble getting this message posted to the list. Not sure what's up with that. -- Danny Sadinoff da...@sadinoff.com
Re: mod_fcgid: different instances of the same program
On Tue, Nov 10, 2009 at 12:53 AM, Jeff Trawick traw...@gmail.com wrote: On Mon, Nov 9, 2009 at 5:16 PM, Danny Sadinoff danny.sadin...@gmail.com wrote: ... 1) symlinks you. It seems that mod_fcgid identifies fcgid programs by inode and device, not by filename. So two fcgid programs invoked by the webserver along different paths will be counted as the same if the two paths are hardlinks or softlinks to each other. Mostly yes. The path to the file doesn't matter; it is the file itself that matters. There are different requirements for how programs are distinguished. One possibility is changing from stat() to lstat() (i.e., distinguish symlinks but not hard links). Another possibility is looking only at the basename. This was discussed in this thread: http://www.mail-archive.com/dev@httpd.apache.org/msg45516.html What are you trying to accomplish which is hindered by the current implementation? My goal is a fairly simple one-application per vhost setup. But, I'm seeing application pools shared amongst virtual hosts with distinct ServerName declarations, all of whom refer to the same file path (and inode) for the fcgi executable. From what you're telling me, this is buggy behavior. I'll try to boil my config down further and come up with a good testcase. Whether my config is wrong or the implementation is buggy, I would think that the mere existance of the dev thread trying to nail down the semantics ought to be argument enough for documenting the file-path-vs-inode behavior. 2) Virtual hosts The above item holds true even across virtual hosts. So while it's possible to adjust the FcgidInitialEnv items on a per-vhost basis, this is a recipe for disaster if two vhosts point at the same fcgi executable, because the resulting processes with potentially different Environments will be inserted into the same pool. Once that occurs, we may expect that a server spawned with config defined in vhost A will be parcelled out to vhost B. Where does this occur? Entries in the process table are distinguished by virtual host. (I think the implementation of this check is broken, in that it requires that ServerName is set in the virtual hosts. Are you using a simple test config that doesn't have ServerName set?) My case is not yet simple. I'll get back to you. The Apache httpd 2.3 docs do not address the symlink issue at all, and the virtual host issue only indirectly. http://httpd.apache.org/mod_fcgid/mod/mod_fcgid.html FWIW, this isn't part of Apache httpd 2.3. mod_fcgid is released separately from the web server and only by coincidence has the same version number (2.3.x) as development levels of the web server. Well, that's another doc bug, since the page I link to has a big header that says: Apache HTTP Server Version 2.3 :) -danny
