From owner-freebsd-questions@FreeBSD.ORG Thu Aug 15 12:53:08 2013 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTP id 77CC5F5A for ; Thu, 15 Aug 2013 12:53:08 +0000 (UTC) (envelope-from frank2@fjl.co.uk) Received: from bs1.fjl.org.uk (bs1.fjl.org.uk [84.45.41.196]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id E8A292DF5 for ; Thu, 15 Aug 2013 12:53:07 +0000 (UTC) Received: from [10.106.97.204] ([46.233.72.141]) (authenticated bits=0) by bs1.fjl.org.uk (8.14.4/8.14.4) with ESMTP id r7FCqwR6022309 (version=TLSv1/SSLv3 cipher=DHE-DSS-CAMELLIA256-SHA bits=256 verify=NO) for ; Thu, 15 Aug 2013 13:52:59 +0100 (BST) (envelope-from frank2@fjl.co.uk) Message-ID: <520CCF37.1000505@fjl.co.uk> Date: Thu, 15 Aug 2013 13:53:11 +0100 From: Frank Leonhardt Organization: Frank Leonhardt User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130801 Thunderbird/17.0.8 MIME-Version: 1.0 To: freebsd-questions@freebsd.org Subject: Re: High availability on remote site References: <20130815071840.26438d9b@tech304.office.supranet.net> In-Reply-To: <20130815071840.26438d9b@tech304.office.supranet.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Content-Filtered-By: Mailman/MimeDel 2.1.14 X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list Reply-To: frank2@fjl.co.uk List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 15 Aug 2013 12:53:08 -0000 On 15/08/2013 13:18, Mark Felder wrote: > On Thu, 15 Aug 2013 18:19:35 +0700 > Olivier Nicole wrote: > >> Hi, >> >> I have been assigned to offer HA on a 3 tiers architecture. >> >> Data storage tier will be MySQL, so replication is easy. >> > Keep in mind that MySQL replication has plenty of its own issues. It > does not replicate every SQL command to the slave. Guaranteeing that > data on both servers is identical is also a very tricky process. You > might want to first browse through the sections here to get an idea: > > http://dev.mysql.com/doc/refman/5.5/en/replication-features.html > > >> HA should be implemented only on the Data storage tier, Active/Active, >> but one of the sites is remote! >> >> When everything is working, each application accesses the local MySQL >> tier, but when the local MySQL becomes unavailable, it should be able >> to automatically move to the other database server. >> >> I have no access to the application, so I cannot modify it to test if >> local MySQL is working. So I should have an HA mechanism that enforces >> changing the IP address on the database server. >> > This is easy. Use HAProxy. It can test to see if your local MySQL > instance is up and running and if it detects it is not it will > automatically pass connections to the remote site's MySQL server. > >> If both servers are installed at different places, with different >> addresses, would there be a way beside establishing an IP tunnel/VPN >> between both places to have all machines in a single subnet? >> > This seems unnecessary. Why do you need them to be on the same subnet? > >> An image is here http://www.cs.ait.ac.th/~on/HA.gif >> >> I am really bothered by the IP tunnel, but that's the only way I see to keep HA. >> > Hopefully I've answered this question for you and you see that you > shouldn't need these to be on the same subnet. > _______________________________________________ > WHS, especially regarding the built-in replication of a mySQL database being problematic. I tried this a few years ago and decided it wasn't worth the candle (for my needs). It came down to the application software needing to be sensitive to the situation - to understand it needed to use a backup server, and to treat it as read-only. The implication is that mySQL could be some kind of distributed cluster until you got to it in detail. Or perhaps I was missing a point somewhere. If you get a "perfect" cluster going please do tell me know how. Incidentally, in the end I just used rsync - much less fuss but only good as a backup, really (which is what I really wanted). Regards, Frank.