People often ask me, "what's so great about AppLogic?" I tell them that aside from it's 5 minute mean-time-to-repair for hardware failures (like a server going down) one of the big advantages is ease of system administration and the ability to avoid unnecessary downtime.  This is why ENKI chose it as the application framework for delivering our Computing Utility product.  I don't usually do much with AppLogic myself, since I am responsible for Sales and Marketing at ENKI.  However, I am also responsible for our corporate website.  So today, I got a demonstration of what AppLogic can do for you - on my own company website - and I wanted to share it with you.

Our company website is hosted in a Virtual Private Data Center, which consists of a number of appliances (virtual servers connected to each other in a private name space): Apache, MySQL, a NAS, a logging server, and a firewall server.  MySQL and Apache mount their data from the NAS.

We had been running our website on Joomla 1.0.12 for a while now.  I noticed recently that our site was getting attacked with exploits that might breach 1.0.12.  Also, there were some bugs in 1.0.12 that I wanted to fix by upgrading to a newer version.  It was time to upgrade Joomla.  Here's how I did it:

- I created a copy of my running VPDC and started it.  This also copied all my data, so the new VPDC had an exact copy of our company website.  My website was still up on the "old" copy.

- I installed the new Joomla onto my copy (by loading it into the appropriate directory on the NAS)

- I tested the new VPDC with the new Joomla in it.

- I altered the IP address of the new VPDC to be that of our main website

- I shutdown the old VPDC and restarted the new one.

The total down time for our website was under a minute, and I had deployed a fully working and tested upgrade!  Joomla is a PHP application, and installing it is basically just a file download and un-tar, followed by some setup work.  But installing a new version of MySQL would have been very similar: in that case, I would simply have instantiated a newer version of the MySQL appliance in my VPDC and restarted it, since all appliances are instances of appliance-objects.

AppLogic's easy copying of a VPDC has other benefits as well.  You can automatically create and provision a copy in order to meet the demands of new customers for a SaaS (software as a service) application that need their own VPDC.  Or, you can copy the VPDC to another physical data center for hot or cold standby purposes.

The biggest obstacle to enjoying these AppLogic advantages is the mental barriers one has around how system administration has always been done, and what operations are possible in an object-oriented virtual operating system.  I often find new ways to shortcut operations that might have been risky or expensive, once ask myself "how is this done in AppLogic?"  To allow our customers to shortcut the need to learn AppLogic, ENKI offers these advantages to our customers without their having to learn AppLogic, since we manage their VPDCs for them.

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e novikoff: Managing Data

Gerard,
In AppLogic when an appliance (virtual server) in a VPDC "goes down" it means something different than under a physical system. Data loss due to hardware failure is a very unlikely scenario under AppLogic since storage is RAIDed across multiple servers. Typically when an appliance goes down, the situation is one of:
- out of resources (usually memory or disk)
- software bug
- intentional or unintentional deletion (including hacking)
In the first two cases, you don't generally lose data. To fix resource issues (after determining they weren't caused by a bug), you change the resource allocation on the offending appliance and restart. This takes less than a minute typically. AppLogic has built-in monitoring that can warn of impending resource issues, so you can usually choose your downtime. In the case of a software bug, you fix the bug and restart, using a procedure similar to the one in the blog article. Again no data loss.

So the interesting situation is if you're hacked or delete your data. AppLogic is not a substitute for a good backup strategy; however, you never need to use backup to restore broken hardware. In AppLogic, you replace the failed hardware and initiate a reintegration process, all of which occurs while your application is running. Because of the reliability of the AppLogic grid storage, backup consists at the minimum of simply instantiating another NAS appliance, or even a special directory in your existing NAS, and writing to it with backup software.

Also, you can back up your entire application (all of the virtual servers, their configs, and their data) so you can restore a hacked site to a prior checkpoint in a couple minutes by restarting the backup.

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January 04, 2008

Gerard Horan: ...

Very interesting article! How do you manage Data? For example if the MySQL instance goes down or you lose the NAS how do you "restore" in those type of scenarios?

2

January 03, 2008

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