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RE: RE : Site Mirroir
That's ok. The first point is mine.
Thanks you a lot. I'll try it
Paul
At 07:02 PM 5/25/2002 +0200, William Stucke wrote:
>Hi Paul,
>
>You are actually describing two SEPARATE issues: -
>
>1 Maintaining two identical copies of a site - called "mirroring".
>2 Directing visitors to the "best" server for the situation - called
>"dynamic DNS", amongst other things.
>
>In order to make (1) - Mirroring - work, you need the following: -
>
>a SERV1 must operate an web site (don't forget the obvious bits!)
>b SERV1 must operate an FTP site, with the content of the web site
>accessible via FTP
>c SERV2 must have the appropriate rights to allow it access to this
>FTP site
>on SERV1
>d SERV2 must run suitable mirroring software (more on that later)
>e Optionally, if certain software is chosen, such a rsync, SERV1
>must ALSO
>run appropriate software
>f SERV2 must operate a web site - the content is identical to that
>on SERV1,
>because it's copied from there
>g SERV2 must have a scheduler (cron works fine, if you are in the UNIX
>world) to cause the mirror software to run at the desired intervals
>
>[You mention hourly updates. Good grief! What are you putting on the site
>that requires such frequent updates? If you want "up to the minute" changes
>to be reflected on both sites, then there are alternative methods, such as
>synchronising a SQL DB]
>
>What mirror software to use?
>
>For UNIX: -
>
>mirror is most common. It's a Perl script, so you must have Perl installed
>on your system to be able to use it. It's a relatively simple FTP folder
>directory comparison tool, that will synchronise the local site to the
>remote site every time it is run. It does this by: -
>
>* Comparing directories on both sites (various packages do either a
>depth
>first or a breadth first comparison. A few allow you to choose which you
>want to use)
>* Copying all new files from the remote site to the local site
>* Copying all changed files (i.e. ones that have a more recent modified
>date) from the remote site to the local site
>* Deleting all files on the local site that no longer exist on the
>remote
>site. CAREFUL! A "broken" run on almost any of these packages can result in
>your entire local site being deleted, if you aren't careful how you set it
>up!
>
>There are several other packages that operate in a similar manner, some of
>which were mentioned on this list.
>
>rsync is different. It works on a "push" basis, rather than the "pull" basis
>of the compare-directories-and-FTP-the-differences packages, like mirror.
>Essentially, the "Server" (SERV1 in your case), sends the "Client" (SERV2) a
>"digest" of the directory contents that have changed since the last update.
>The "Server" therefore needs to: -
>
>* Keep track of when the Client lost connected, and what files it
>downloaded
>* Scan its own log files in order to generate the digest for the Client
>
>This means that rsync requires MUCH more processing on the part of the
>Server, but the Client needs to transfer less data and do less work, since
>it doesn't have to read and compare every directory.
>
>By way of comparison, if you are mirroring something like TUCOWS, the
>directories alone represent several tens of MB of data, and up to 30 minutes
>of downloading and comparing, before actual file transfer takes place,
>depending on CPU & WAN speed.
>
>For Windows: -
>
>NetLoad is one of the best, but many packages will do it, such as Cute FTP
>and even GetRight. They work in the same way as that described for mirror
>above.
>
>
>Now to the second issue - redirection.
>
>The way this is USUALLY done is with a "Server Farm", i.e. several servers
>behind a single "switch". The switch directs requests to whichever server is
>(a) least heavily loaded and (b) is currently online. This is often
>implemented for either load-sharing or redundancy purposes.
>
>You can't do that, if your two servers are on different networks. In that
>case, your best bet is probably "dynamic DNS". Essentially, this means that
>a name server is responsible for directing requests to the "best" server,
>depending on load, speed, and availability.
>
>The problem with this scenario is DNS caching. Most name servers will cache
>(remember) a recent name lookup, so if your dynamic DNS changes which server
>it wants to send requests to, it will be ignored by anyone who has been
>there recently. Of course, NEW visitors will be sent to the right server.
>
>I'm by no means an expert on the subject. Best to ask someone who knows much
>more than I do, like Alan Barrett.
>
>BTW, Windows 2000 implements dynamic DNS natively, and relatively
>painlessly.
>
>Hope that helps. Bon chance!
>
>Regards,
>
>William Stucke
>ZAnet Internet Services (Pty) Ltd
>mailto:William at zanet.co.za
>+27 11 465-0700
>
>
>-----Original Message-----
>From: owner-afnog at afnog.org [mailto:owner-afnog at afnog.org]On Behalf Of
>Paul Dégbé KPOGNON
>Sent: 2002/05/25 16:28
>To: Noah K Sematimba
>Cc: afnog at afnog.org
>Subject: Re: RE : Site Mirroir
>
>
>No, my problem is this.
>Let me give clearly an example.
>
>I have a web site on my webserver called SERV1. The URL to reach the site
>is www.web1.com.
>Now i want to have a mirror of that web site on another server named SERV2
>on a remote ISP network. The transfert will be done automatically each hour.
>If somebody want to visite my web site, he only know one address :
>www.web1.com.
>And that address can call SERV1 or SERV2 depending of the following
>situations : SERV1 is down and SERV2 is up (so SERV2 will respond), SERV2
>is more quick than SERV1 (so SERV2 will respond), unless SERV1 will respond.
>
>Now my problem is :
>
>1 - What do I need to have like packages for that?
>2 - Which mirror configuration each of the both servers SERV1 and SERV2
>will have?
>
>I think I more and more clear.
>
>Thanks you for your help
>
>Paul
>
>At 05:12 PM 5/24/2002 +0300, Noah K Sematimba wrote:
>
> > > Now like I have said, I would like to get experience from those who have
> > > installed yet MIRROR.
> > > What is the procedure and witch packages is needed and where to find
>those
> > > packages?
> >
> >If you're talking about the package called mirror. You simply need the
> >package mirror itself and also to run an ftp server. Problem with this is
> >the usual fact that ftp is unencrypted thus all ytour stuff is cleartext.
> >
> >You could use sitecopy and if the web server has DAV support that is an
> >option. Since in that case you could use ssl.
> >
> >Noah.
> >
> >
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