Login | Register For Free | Help
Search for: (Advanced)

Mailing List Archive: Linux-HA: Users

Basic Linux-HA architecture

 

 

Linux-HA users RSS feed   Index | Next | Previous | View Threaded


tpo2 at spin

Mar 13, 1998, 1:27 AM

Post #1 of 1 (545 views)
Permalink
Basic Linux-HA architecture

On Fri, 13 Mar 1998 alanr [at] bell-labs wrote:

> Second: It seems that having Dynamic DNS would be most beneficial for such as
> system, especially when one has a round-robin DNS configuration and wants to
> gracefully shutdown a node for maintenance. What you want to do is:

While this is a good idea, it will only work partially I think. From my
experience there are quite a few systems that will not update their DNS
cache when they (by spec) should so you've allways got a delay. Among
others various browsers have (so it seems to me) internal DNS caches, that
don't get updated.

I can't prove you this with facts, it's just my experience. Maybe someone
knows more.

I think it's got to be an IP take over or a redistribution of services
with for example rinetd.
*
t

"This Perl language is wonderful. Where can I get it - from Microsoft?"
--------------------------------------------------------------------------------
Tomas Pospisek's mailing-lists mailbox
www.SPIN.ch - Internet Services in Graubuenden/Switzerland
--------------------------------------------------------------------------------


From Alan Robertson <alanr [at] bell-labs> Fri Mar 13 13:07:37 1998 [67]
From: Alan Robertson <alanr [at] bell-labs> (Alan Robertson <alanr [at] bell-labs>)
Date: Fri, 13 Mar 1998 14:07:37 +0100
Subject: Basic Linux-HA architecture
In-Reply-To: <Pine.LNX.3.95q.980313082130.29058A-100000 [at] spin>
Message-ID: <ML-3.3.889794457.7349.alanr [at] alanrhome>

Tomas Pospisek wrote:
> On Fri, 13 Mar 1998 alanr [at] bell-labs wrote:
>
> > Second: It seems that having Dynamic DNS would be most beneficial for
> > such as system, especially when one has a round-robin DNS configuration
> > and wants to gracefully shutdown a node for maintenance. What you want to
> > do is:
>
> While this is a good idea, it will only work partially I think. From my
> experience there are quite a few systems that will not update their DNS
> cache when they (by spec) should so you've allways got a delay. Among
> others various browsers have (so it seems to me) internal DNS caches, that
> don't get updated.
>
> I can't prove you this with facts, it's just my experience. Maybe someone
> knows more.
>
> I think it's got to be an IP take over or a redistribution of services
> with for example rinetd.

Ahhh... That's with conventional DNS. Dynamic DNS is an enhancement to DNS
that sends out updates to DNS without doing entire zone transfers. It is
designed to work correctly in a DHCP environment, where name to IP addresses
are (potentially) constantly changing. You can read an overview of it at:
http://davidsimmons.com/tips/081797/

I don't think applications cache DNS entries, BUT DNS servers do (by design).
Dynamic DNS is supposed to make this work - when you have it deployed
throughout your infrastructure.

Returning to the proposal:
I believe that the ability to do graceful shutdown is a useful one, and it
requires a third state - and that IP address takeover not occur until after the
graceful shutdown has (by some definition) completed. It seems to me that IP
address takeover is the "kill -9" of the HA world. It shuts the water off,
without any chance for the clients to take graceful recovery action.

The OOS state allows applications to "save their files" or whatever, and
gracefully reconfigure themselves for the new HA configuration, while still
being able to communicate over already-established communication paths. Until
you have Dynamic DNS, it may simply be that the servers send information to
their clients notifying them of the impending shutdown, but even that's better
than nothing.

IMHO, such a capability seems worth architecting in.


-- Alan Robertson
alanr [at] bell-labs



From Alan Robertson <alanr [at] bell-labs> Fri Mar 13 13:28:51 1998 [68]
From: Alan Robertson <alanr [at] bell-labs> (Alan Robertson <alanr [at] bell-labs>)
Date: Fri, 13 Mar 1998 14:28:51 +0100
Subject: Small Linux-ha web site?
Message-ID: <ML-3.3.889795731.3978.alanr [at] alanrhome>

A couple days ago, someone had pointed at a small Linux-HA web page that they'd
created. I foolishly deleted his mail.

Who was that, and where was the page?


Thanks!!


-- Alan Robertson

Linux-HA users RSS feed   Index | Next | Previous | View Threaded
 
 


Interested in having your list archived? Contact Gossamer Threads
 
  Web Applications & Managed Hosting Powered by Gossamer Threads Inc.