On Sat, Oct 11, 2008 at 08:38:52PM +0800, Tim Post wrote:
> On Sat, 2008-10-11 at 04:31 -0700, Jeremy Chadwick wrote:
> > Is solving this problem *really* the job of a web server?  The answer to
> > this question should be: no it is not.
> 
> Is that so?
> 
> > 
> > The web server should handle web server "things".
> 
> Updating a single text configuration file from a central point is not a
> 'thing' for web servers to do ?

No.  Web servers serve content; web servers do not distribute files to
other machines.

> > What you're
> > describing is the need for either:
> > 
> > 1) A series of administrative scripts that can distribute configuration
> > files to numerous servers when changes are made.  This is how a lot of
> > companies do it.  Have you looked at cfengine?  Please do.
> 
> And years ago we made fire with sticks. Yes, I have looked at it.

Administrative scripts are not something from the 70s.  They are a key
piece of problem-solving and administrative task completion on UNIX.
If you are a system administrator who does not know shell scripting or
how to use utilities like scp or rsync, you likely shouldn't be the sole
administrator of a system (you should be a junior SA and have someone
senior above you who can "show you the ropes").

> > 2) A network-distribution filesystem with no single point of failure.
> > DragonflyBSD's HAMMER filesystem can do this I think, FreeBSD has
> > ggatec/ggated, and Linux has some software which can do it as well.
> > Note that I'm not mentioning NFS because an NFS server is a single
> > point of failure (although many companies live with this reality and
> > buy something like a Network Appliance filer which is reliable).
> 
> And just to run a reliable web site, you should have to endure this ..
> why?  Someone hoping to start the next (name some popular thing) should
> have to endure this why? Do they not deserve reliability without
> mastering their operating system?

Item #1 does not require "mastering their operating system".  It
involves using the *right* software to accomplish the task at hand; why
does the web server need to do this job?  Why can you not rsync a file
to another machine or series of machines using a script, which also
SIGHUP the daemon so it re-reads the updated configuration file?

This is in no way "mastering an operating system" -- this is being a
system administrator.  Seriously: this task is VERY simple to
accomplish, even in the most bare-bones environments.  I recommended
cfengine because that software suite was *specifically* engineered to
solve the complexities of managing configuration files across multitudes
of machines.  Use the right tool for the job!

Item #2 does add more complexity to the task at hand -- you are
absolutely right.  I simply offered it as a "lazy alternative" -- you
set it up once, it starts working, and *ANY* program will work.  You
do not need to tell the web server about configuration files or what
servers to distribute things to or other such nonsense; you edit a file,
it gets distributed to the remote system automatically at the filesystem
level, transparently.

> What is so inherently wrong about propagating a configuration change to
> many nodes, without dlm, such as ocfs2 does now? Why even bother with
> the overhead of a cluster or network file system when one is not needed?

One of UNIX's many concepts is to keep things segregated, separate,
and layered -- while providing ways for each individual thing to talk
to another thing using pipes or domain sockets.

A web server's job is to serve content over HTTP, not to do things like
distribute configuration file changes to machines over a network.
Distributing files to multitudes of machine is not the job for a web
server.

-- 
| Jeremy Chadwick                                jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |

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