[Linux-HA] ('Lil bit off-topic) HA using round-robin -- working!

[Robert Heinzmann]

Hi,

why not really USE the hot standby ?

Just configure 2 resource groups, each protected by an HA solution. So 
you have 2 Apache running, each one using a floating IP address. In DNS 
you configure both of them with A records for the same domain (as you 
already did). Now both machines "do something" and in case one machine 
fails, the other one hosts both apache servers.

Is'nt this better ?

If the machines differ in computing power, you can also you more A 
record, according to the capabilities of the servers. Lets say Server A 
is 2 times faster than 2, you can configure this in DNS:

1.1.1.1 www.domain.com
1.1.1.1 www.domain.com
1.1.1.2 www.domain.com

Regards,
Robert

Chris de Vidal schrieb:
> I've been experimenting with multiple A records for both load-distributing AND high availability.
>
> Up until this point I was always told that round-robin is for load-distributing ONLY and should
> not be used for high availability failover. But in practice this is not proving to be true. I'm
> beginning to think that was just FUD.
>
> Do a lookup on roundrobintest8.strangled.net and roundrobintest9.strangled.net. Notice the A
> records: 
> roundrobintest8.strangled.net. 3600 IN A 127.0.0.1 
> roundrobintest8.strangled.net. 3600 IN A 63.95.68.129 # Real server 
> roundrobintest9.strangled.net. 3600 IN A 10.69.96.69  # Bogus IP 
> roundrobintest9.strangled.net. 3600 IN A 63.95.68.129 # Real server
>
> Now, disable anything running on localhost:443 and make sure you do *not* have a host at
> 10.69.96.69.
>
> Browse https://roundrobintest8.strangled.net/ and https://roundrobintest9.strangled.net/ You
> should never get a DNS error. It should always give you first an SSL warning (hostname mismatch)
> and login prompt. Oh it'll pause while it tries the bad IP but after about 5 seconds it flips to
> the real server.
>
> Now load up an SSL web server on localhost. I used Apache+mod_ssl on Linux and TinySSL on Windows.
> Set up an index page with links to several other pages.
>  
> (Sorry to require SSL, it was the only web server I have control over that no one is using at the
> moment, so I can kill the web service any time I want... You could also load up an FTP or SSH
> server on localhost instead of SSL. My server has all three.)
>
> Flush your cache (e.g. ipconfig /flushdns) and reload the website. Sometimes you will get
> localhost, sometimes my server. That's the load-distributing action we all know and love.
>
> If you don't get localhost, keep flushing your cache until you get it. Then kill your server and
> click on a link in the web page that is still up on your screen. It will fail back to my server
> and generate a 404. That's high availability! Even though it generates an error, it's coming from
> my server nonetheless!
>
> -No- client I've tried (browser, FTP client, MySQL, SSH etc.) fails on the bad IP (10.69.96.69).
> It thinks for a few seconds and then tries the good IP.
>
> Nor does it fail when the IP is good, as in the case of localhost, but no service is listening on
> that port.
>
> I've tried this on: 
> Windows 95 
> Windows 98 
> Windows 2000 
> Windows XP 
> Ubuntu 6.06 
> Debian 3.1 
> CentOS 3 
> CentOS 4
>
> With these clients: 
> Netscape 4.5 (Nice and old!!!) 
> IE 5.5 
> IE 6 
> Firefox 1.0 
> Firefox 1.5 
> DOS FTP 
> Linux FTP 
> Linux NcFTP 
> MySQL client 
> OpenSSH client
>
> My idea is to set up a live server running web/mail/DNS/DB/FTP and a warm standby, such as: 
> www.example.com. 3600 IN A 1.1.1.1 
> www.example.com. 3600 IN A 2.2.2.2
>
> The warm standby is powered on but no services are started. Live is synchronized to warm standby.
> If the live fails I bring up the standby. Bing bang boom, the client automatically goes to the
> standby.
>
> It'll be just web/POP/SSH/FTP because DNS and SMTP already have built-in load-distributing and
> high availability capabilities. No database ports will be exposed to the outside world but if I do
> they should work.
>
> If this works, so cool! Replacement for expen$ive and complicated HA solutions :-)
>
> Was clued into this by Mr. Tenereillo:
> http://www.tenereillo.com/GSLBPageOfShame.htm
>
> What am I missing? Do I need to do more testing?
>
> Am I crazy? Or crazy like a fox? ;-)
>
> Someone check me on this because I'm not sure I'm testing it right...
>
> CD
>
> Are you good enough?
> TenThousandDollarOffer.com
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