Date: Thu, 15 Aug 2013 13:53:11 +0100 From: Frank Leonhardt <frank2@fjl.co.uk> To: freebsd-questions@freebsd.org Subject: Re: High availability on remote site Message-ID: <520CCF37.1000505@fjl.co.uk> In-Reply-To: <20130815071840.26438d9b@tech304.office.supranet.net> References: <CA%2Bg%2BBvgzr_hkpm5c6tgwSPLRcPa1Mre-8XZ3SRS%2BE20DASDe_A@mail.gmail.com> <20130815071840.26438d9b@tech304.office.supranet.net>
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On 15/08/2013 13:18, Mark Felder wrote: > On Thu, 15 Aug 2013 18:19:35 +0700 > Olivier Nicole <olivier.nicole@cs.ait.ac.th> 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.
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