Date: Tue, 16 Jan 2018 19:32:05 -0500 From: Chris Gordon <freebsd@theory14.net> To: "Zainelabdeen S.A Elgraeed" <zainco30@gmail.com> Cc: freebsd-questions@freebsd.org Subject: Re: HAST questions Message-ID: <6C4AA002-7CB2-4506-AA7C-722083197BA0@theory14.net> In-Reply-To: <CAMq=vKGjoheaiS-0TaVj-RH3MUiXwYdC656nuMpJM4y_VwfU5w@mail.gmail.com> References: <CAMq=vKEbUeZL9DsutYZ4guMdPk9yK2YjLpsGwWzp1f7nuiBoBQ@mail.gmail.com> <1DFDF803-4D86-42F8-A22E-4A9077608982@theory14.net> <CAMq=vKGjoheaiS-0TaVj-RH3MUiXwYdC656nuMpJM4y_VwfU5w@mail.gmail.com>
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> On Jan 12, 2018, at 1:10 AM, Zainelabdeen S.A Elgraeed = <zainco30@gmail.com> wrote: >=20 > > It really depends on the details of the application on what options = you have and what the best way to do this may be. > we host dynamic content with MySQL databases like Moodle and OJS. >=20 > I want for storage to be active/active but HAST is master/backup so I = can be used for failover only. > is HAST support DRBD ? or what another technology can use for HA and = LB for storage? The exact solution can be somewhat dependent on your specific = environment, but I=E2=80=99d start looking at: - Run the web servers (apache, nginx, whatever) active in both/all jails = and distribute traffic to them with some kind of load balancer = (commercial appliance, other machines running ha-proxy or the like). - Run one master DB and one standby DB with database replication = replicating content between the two. Most RDBMs support some kind of = replication including MySQL. - With MySQL you can do reads from both the active and standby nodes, = but write to only the master. It depends on your particular application = if/how you can configure the application to take advantage of the slave = reads. - In the event of the failure of one of the hosts, you only need to = worry about switching the roles of the DB and potentially re-pointing = the applications if the primary DB node is the one that goes away. - I would consider putting the database servers and web servers in = different jails. This lets you scale them, add resource controls if = appropriate, move them, etc independently. I prefer database/application replication over storage replication in = most use cases since storage replication will often dutifully = replication file system and other problems for you. Database = replication typically gives you some additional independence between = your nodes and reduces certain chances of fault replication. Regardless = of which you choose, you need to make sure you exercise and understand = the many failure cases you can end up in and know how to recover the = system. Also remember that replication like this is NOT a backup -- be = sure to also have a good back (and recovery) plan. Active/Active is another can of worms. Active/Active storage for writes = is a very difficult problem. Even if someone said they have it, I=E2=80=99= d be very careful with all of the corner cases and failure modes. = Active/Active databases do exist (MySQL has Galera, I believe Postgres = has a paxos based solution), but again you get a lot of additional = complexity and need to really understand and test the solution before = using it. Hope that helps. Chris
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