That's right. However, you could just use a single server. For example, base it on the app role, have Scalr automatically connect an EBS store (e.g. to / mnt/storage) and then make the MySQL data dir a sym link from /var/lib/ mysql -> /mnt/storage/var-lib-mysql (or whever you call the directory). Then use the 'sync-to-all' feature of Scalr to rebundle it as a new role (my-web-mysql or whever).
This will not provide true HA (High Availability), because if the instance should go down for whatever reason, it could be as long as 10-15mins before Scalr has noticed, started a replacement instance and mounted the EBS. Probably also want to use a script to start the mysql server on the EBSMounted event from the Scalr farm settings (so it doesn't start before the data dir exists). In my experience, EC2 instances only go down unexpectedly vary rarely (probably when the physical hardware it is running on fails, looses power or Amazon has some problem with their service). I've only see it happen once and that was when EC2 was in beta. Note also that EBS is a 'dumb' block-device, so if an instance crashes, it could in theory leave the filesystem in a corrupted state that can't be remounted. So, use a journalled filesystem like ext3 to make that extremely unlikely (the default anyway). Finally, an EBS store can actually fail, though Amazon says their reliability approximates 10x more reliable that a physical Hard Drive. Hence, you probably want to enable the Scalr 'auto snapshot' feature to automatically take an EBS snapshot (which is stored in S3) periodically, so that if disaster strikes (meteor hits the Amazon facility where your instance & EBS reside), you'll still be able to create a new EBS volume in another availability zone from the last snapshot (manually). You will also be able to grow your system (manually) in future, should the need rise. Just fire up some Scalr mysql role instances, setup the master with a copy of your DB and temporarily make it also a slave to your existing DB - then just switch the app code to point to the new DB master. Then just add more app instances and point them all to the mysql master/slave hosts. So, with one EC2 instance, if you reserve it, you likely be running for less than US$40/mo + Scalr fees. Hope that helps, -David. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "scalr-discuss" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/scalr-discuss?hl=en -~----------~----~----~----~------~----~------~--~---
