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I've been playing around with a free account on appfog.com and this question came to mind.

What's the difference between scaling memory and scaling instances?

For example, what is the real world performance and reliability difference between these 3 examples?

1 instance with 512MB.

2 instances with 256MB each.

4 instances with 128MB each.

If there is no difference, why wouldn't you keep upgrading 1 instance to the maximum amount of memory before scaling out to 2 instances? That would seem like the simplest approach from a management perspective.

Thanks in advance for your answers!

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2 Answers 2

up vote 1 down vote accepted

Multiple instances means redundancy - if one crashes, the rest continue serving your content.

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What are the chances of an instance crashing if they're all on the same server running the same code? With appfog and other cloud hosting services like this, you first choose your server then all instances are just running at the same place. –  Pepper Jan 28 '13 at 15:00
    
@Pepper Bad data could easily crash one instance and leave the others standing... and since Appfog is running on Amazon AWS, I doubt they're all running on the same physical server, as AWS doesn't let you pick. –  ceejayoz Jan 28 '13 at 15:31
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You could be bottlenecking on something other than memory. Like CPU, or open file handles, or other things that have nothing to do with the amount of RAM at all.

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I dont have an issue with performance, this is just a "theory" question before I actually set the servers up. –  Pepper Jan 28 '13 at 14:58
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