Basic AWS questions

Question

I'm newbie on AWS, and it has so many products (EC2, Load Balancer, EBS, S3, SimpleDB etc.), and so many docs, that I can't figure out where I must start from.

My goal is to be ready for scalability.

1. Suppose I want to set up a simple webserver, which access a database in mongolab. I suppose I need one EC2 instance to run it. At this point, do I need something more (EBS, S3, etc.)?

2. At some point of time, my app has reached enough traffic and I must scale it. I was thinking of starting a new copy (instance) of my EC2 machine. But then it will have another IP. So, how traffic is distributed between both EC2 instances? Is that did automatically? Must I hire a Load Balancer service to distribute the traffic? And then will I have to pay for 2 EC2 instances and 1 LB? At this point, do I need something more (e.g.: Elastic IP)?

Answer 1

Welcome to the club Sony Santos,

AWS is a very powerfull architecture, but with this power comes responsibility. I and presumably many others have learned the hard way building applications using AWS's services.

You ask, where do I start? This is actually a very good question, but you probably won't like my answer. You need to read and do research about all the technologies offered by amazon and even other providers such as Rackspace, GoGrid, Google's Cloud and Azure. Amazon is not easy to get going but its not meant to be really, its focus is more about being very customizable and have a very extensive api. But lets get back to your question.

1. To run a simple webserver you would need to start an EC2 instance this instance by default runs on a diskdrive called EBS. Essentially an EBS drive is a normal harddrive except that you can do lots of other cool stuff with it like take it off one server and move it to another. S3 is really more of a file storage system its more useful if you have a bunch of images or if you want to store a lot of backups of your databases etc, but its not a requirement for a simple webserver. Just running an EC2 instance is all you need, everything else will happen behind the scenes.

2. If you app reaches a lot of traffic you have two options. You can scale your machine up by shutting it off and starting it with a larger instance. Generally speaking this is the easiest thing to do, but you'll get to a point where you either cannot handle all the traffic with 1 instance even at the larger size and you'll decide you need two OR you'll want a more fault tolerant application that will still be online in the event of a failure or update.

   If you create a second instance you will need to do some form of loadbalancing. I recommend using amazons Elastic Load Balancer as its easy to configure and its integration with the cloud is better than using Round Robin DNS or a application like haproxy. Elastic Load Balancers are not expensive, I believe they cost around $18 / month + data that's passed between the loadbalancer.

   But no, you don't need anything else to do scale up your site. 2 EC2 instances and a ELB will do the trick.

Additional questions you didn't ask but probably should have.

1. How often does an EC2 instance experience hardware failure and crash my server. What can I do if this happens?

   It happens frequently, usually in batches. Sometimes I go months without any problems then I will get a few servers crash at a time. But its defiantly something you should plan for I didn't in the beginning and I paid for it. Make sure you create scripts and have backups and a backup plan ready incase your server fails. Be ok with it being down or have a load balanced solution from day 1.

2. Whats the hardest part about scalabilty?

   Testing testing testing testing... Don't ever assume anything. Also be prepared for sudden spikes in your traffic. You have to be prepared for anything if you page goes from 1 to 1000 people over night are you prepared to handle it? Have you tested what you "think" will happen?

Best of luck and have fun... I know I have :)