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If I have an AMI (EBS backed) from which I launch two instances, would both instances be entirely separate from each other? How does the underlying infrastructure work?

I find it a little overwhelming to get the entire idea to picture. Yes, I'm new to this whole AWS thing.

ЯegDwight
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softie
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2 Answers2

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Yes, they're essentially like "twins" - both are made from the same genetic material (AMI) but each one is an individual person (server). Each instance must be completely decoupled from each other and able to survive on it's own without any knowledge or dependency on it's "twins" (other instances), otherwise you're heading into "conjoined twins" territory in the case of this metaphor!

Assuming each of these instances is for a web server, the thing that binds all of your instances together in the infrastructure is a "Load balancer". This is what will receive the requests to your application and pass it on to one of the web server instances - typically the one that is the least busy.

e.g.

load balancer diagram

Obviously there's much more to it than this, but this is the general idea.

RobMasters
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  • thanks, that really helped. I shared an AMI on one account with another account. Do you know if there would be any permission issues on the destination? Because I launched an instance from the shared AMI on the destination account, but I am not able to SSH to this instance. So that's what led me to wonder if 2 instances on the same AMI would be possible. Since it is, I assume this is another issue. Any ideas? – softie Dec 19 '12 at 16:59
  • It shouldn't matter where you got the AMI from. If you're unable to access an instance via SSH then it's likely that it's security group isn't set up correctly. I'm no expert so I can't offer much help I'm afraid, but just check whether the security settings allow access via port 22 (SSH) and also that it's expecting the correct security certificate (.pem file) – RobMasters Dec 19 '12 at 17:05
  • @softie: New questions (AMI permissions between accounts) would better be asked as new questions instead of in comments. That way others can see the question and answer them. Also consider asking the questions on serverfault.com which is more appropriate for non-programming topics. – Eric Hammond Dec 19 '12 at 23:10
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Just an addition that if you have ip/DNS specific things in your AMI instance that yes, you would have to edit those after the new EC2 was created.

Mauvis Ledford
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