+ Post New Thread
Results 1 to 14 of 14
How do you do....it? Thread, High Availability Moodle in Technical; Has anybody managed to achieve this? I'm thinking to setting up a couple of webservers which point over iscsi to ...
  1. #1

    glennda's Avatar
    Join Date
    Jun 2009
    Location
    Sussex
    Posts
    7,817
    Thank Post
    272
    Thanked 1,138 Times in 1,034 Posts
    Rep Power
    350

    High Availability Moodle

    Has anybody managed to achieve this?

    I'm thinking to setting up a couple of webservers which point over iscsi to a (QNAP?) NAS which will hold /moodledata (possibly using Oracle Cluster file system) then have the mysql databases replicated between then two webservers (one just being a decent specced old desktop) and then once the actual webserver goes down the Second promotes itself to be publicly accessible and as soon as the other comes back online it reverts back to being a slave.

    Also looking to possibly do this with joomla/drupal or similar depending on what we use for our new website.

  2. #2

    dhicks's Avatar
    Join Date
    Aug 2005
    Location
    Knightsbridge
    Posts
    5,664
    Thank Post
    1,263
    Thanked 786 Times in 683 Posts
    Rep Power
    237
    Quote Originally Posted by glennda View Post
    I'm thinking to setting up a couple of webservers which point over iscsi to a (QNAP?) NAS which will hold /moodledata (possibly using Oracle Cluster file system)
    I've not had any experience with Oracle Clsuter File System, but is the idea that it provides fail-over capabilities itself? I don't quite get how that works with iSCISI? You might do better to run your cluster file system over your two web servers, leaving the QNAP out of it, if you just want fail-over capabilities.

    then have the mysql databases replicated between then two webservers
    The simplest way to do this is to mirror an entire block device between servers with DRBD - that way you don't need to set up a cluster file system or SQL replication, your application just reads and writes the harddrive as normal. Disk read operations should have good performance, too, running at local speed, although disk writes have to wait while the write is replicated over the network between the two mirrored devices. You might well get better write performance from a clustering file system and SQL replication.

    Mirroring two servers, with one standing by in case of a problem, is good but somewhat ineffcient. If you're going to set up a clustering file system you might as well look at having two (or more, if you want to make proper use of a central iSCISI-connected storage unit) web servers running, both fielding requests.

  3. #3

    glennda's Avatar
    Join Date
    Jun 2009
    Location
    Sussex
    Posts
    7,817
    Thank Post
    272
    Thanked 1,138 Times in 1,034 Posts
    Rep Power
    350
    Quote Originally Posted by dhicks View Post
    I've not had any experience with Oracle Clsuter File System, but is the idea that it provides fail-over capabilities itself? I don't quite get how that works with iSCISI? You might do better to run your cluster file system over your two web servers, leaving the QNAP out of it, if you just want fail-over capabilities.
    The File System Cluster just means that both can read/write to the same block and talk to each other regarding locked files etc (I use it for all my VM hosting on the SAN)
    It doesn't replicate the data across anything. (is a single point of failure but at least the front end is up which is my main concern!)

    I can then Store the Web files on the Same Block and both webservers read to the same install but have there own copies of the database?

    Does that make sense?

    This would work fine but i'm sure

  4. #4

    dhicks's Avatar
    Join Date
    Aug 2005
    Location
    Knightsbridge
    Posts
    5,664
    Thank Post
    1,263
    Thanked 786 Times in 683 Posts
    Rep Power
    237
    Quote Originally Posted by glennda View Post
    The File System Cluster just means that both can read/write to the same block and talk to each other regarding locked files etc
    Ah, I'm with you.

    I can then Store the Web files on the Same Block and both webservers read to the same install but have there own copies of the database?
    I.e. the primary server has its own copy of the database, which is replicated to a secondary machine for failover puposes. If the primary web server goes down, the secondary one picks up from where it left off.

    If you separate the database server off into its own VM, possibly still replicated between physical machines, you then have two web servers which can be used to simultaniously handle traffic. As long as all user session information is written to that database, not just held in RAM by Moodle, you could have any number of "processing" machines all using the one backend datbase server.

  5. #5

    glennda's Avatar
    Join Date
    Jun 2009
    Location
    Sussex
    Posts
    7,817
    Thank Post
    272
    Thanked 1,138 Times in 1,034 Posts
    Rep Power
    350
    That's a good idea. My webservers are physical as they also run as squid proxies!

    What do you think of the below?

    Has anybody actually tried this?
    Attached Images Attached Images

  6. #6

    dhicks's Avatar
    Join Date
    Aug 2005
    Location
    Knightsbridge
    Posts
    5,664
    Thank Post
    1,263
    Thanked 786 Times in 683 Posts
    Rep Power
    237
    Quote Originally Posted by glennda View Post
    What do you think of the below?
    Looks about right - you'll need something in front of the two web servers to direct requests at each server. Probably just a plain round-robin selection process, i.e. first request goes to A, second goes to B, third goes to A, etc - some DNS servers do round-robin, you could investigate that.

    Your next place to check should probably be the Moodle community to see if anyone's tried running multiple web servers with a common database / file system backend. I've got a feeling I've seen it at least discussed a couple of times before.

  7. #7

    glennda's Avatar
    Join Date
    Jun 2009
    Location
    Sussex
    Posts
    7,817
    Thank Post
    272
    Thanked 1,138 Times in 1,034 Posts
    Rep Power
    350
    Yup I realised that when I posted! My Bad - was just going to put something in front of them to load balance maybe HA proxy.

    I'll check out the moodle site.

  8. #8
    Butters's Avatar
    Join Date
    Jun 2008
    Location
    London
    Posts
    534
    Thank Post
    15
    Thanked 51 Times in 45 Posts
    Rep Power
    60
    Are you a particularly busy Moodle site? Large FE college's tend to go down a lesser route than this for their installs.

    Are you running Moodle on Windows or Linux?

  9. #9

    glennda's Avatar
    Join Date
    Jun 2009
    Location
    Sussex
    Posts
    7,817
    Thank Post
    272
    Thanked 1,138 Times in 1,034 Posts
    Rep Power
    350
    Quote Originally Posted by Butters View Post
    Are you a particularly busy Moodle site? Large FE college's tend to go down a lesser route than this for their installs.

    Are you running Moodle on Windows or Linux?
    Its not going just to be moodle - we are looking at other websites/apps that will need HA as it is going to be used throughout the school day/evening.

    its going to be hosted on Linux

    Toby

  10. #10

    glennda's Avatar
    Join Date
    Jun 2009
    Location
    Sussex
    Posts
    7,817
    Thank Post
    272
    Thanked 1,138 Times in 1,034 Posts
    Rep Power
    350
    Also I'm not sure how can judge busy as i'm not sure what you class as busy - but we are soon to have 15 ICT suites with scheduled classes for 85% of the time with most of the work to rely on moodle. Then we are also introducing Mahara for Years 11 through to 13. Plus are hosting Multiple Websites for lots of school services.

  11. #11
    mrverrall's Avatar
    Join Date
    Feb 2011
    Location
    Lancaster
    Posts
    16
    Thank Post
    2
    Thanked 1 Time in 1 Post
    Rep Power
    0
    Just a few points spring to mind;

    * OCFS is for data clusters... not multiple clients, i.e. primary/primary DRBD clusters. For your purpose NFS will be just fine and you can do away with iscsi entirely.
    * For the DB mysql multi master is just begging for dataloss; I would take a good look at postgres 9 with streaming replication.
    * As you only have one data-store you've not achieved HA; without this it all seems a bit pointless.
    * HAProxy will work great, but have you thought about how you'll fail-over the service IP? You'll need something to do VRRP for you.

    Hope that's helpful!

    Paul

  12. #12

    Join Date
    Feb 2014
    Posts
    2
    Thank Post
    0
    Thanked 0 Times in 0 Posts
    Rep Power
    0
    Quote Originally Posted by mrverrall View Post
    Just a few points spring to mind;

    * OCFS is for data clusters... not multiple clients, i.e. primary/primary DRBD clusters. For your purpose NFS will be just fine and you can do away with iscsi entirely.
    * For the DB mysql multi master is just begging for dataloss; I would take a good look at postgres 9 with streaming replication.
    * As you only have one data-store you've not achieved HA; without this it all seems a bit pointless.
    * HAProxy will work great, but have you thought about how you'll fail-over the service IP? You'll need something to do VRRP for you.

    Hope that's helpful!

    Paul

    OCFS2 is for multiple clients and not data clusters. Yes one can use DRBD with OCFS2, but on its own OCFS2 is just a cluster aware file system with locking. It knows that more than one node will be accessing the same disk and uses file locking.

    It works perfectly well with a shared disk on multiple web nodes, I have built dozens of Moode setups using 2 x web nodes both sharing a disk across a SAN using OCFS2

  13. #13

    Join Date
    Feb 2014
    Posts
    2
    Thank Post
    0
    Thanked 0 Times in 0 Posts
    Rep Power
    0
    Quote Originally Posted by mrverrall View Post
    Just a few points spring to mind;

    * As you only have one data-store you've not achieved HA; without this it all seems a bit pointless.

    Paul
    Sorry but if the OP uses a shared disk, using web node one as the master for adding the disk as "Thick Provision Eager Zeroed" and then adds that disk to the second node by just browsing to it then there is HA as any node can go down and the other node will still have access to disk

  14. #14
    mrverrall's Avatar
    Join Date
    Feb 2011
    Location
    Lancaster
    Posts
    16
    Thank Post
    2
    Thanked 1 Time in 1 Post
    Rep Power
    0
    Even when I read back what I wrote it makes no sense to me either.

    Thanks for the corrections.

SHARE:
+ Post New Thread

Similar Threads

  1. Computer Availability
    By dsm in forum General Chat
    Replies: 10
    Last Post: 15th May 2011, 08:08 PM
  2. Backup Recovery and Availability
    By ict_support in forum How do you do....it?
    Replies: 0
    Last Post: 10th June 2010, 11:27 AM
  3. Monarch Lapcabby availability
    By bert113 in forum General Chat
    Replies: 1
    Last Post: 1st October 2009, 10:59 AM
  4. XP availability
    By Pete10141748 in forum Windows
    Replies: 35
    Last Post: 21st January 2008, 09:34 AM
  5. XBOX 360 availability?
    By in forum Gaming
    Replies: 2
    Last Post: 7th December 2005, 11:40 AM

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •