I have a rails application running on a single VPS that uses passenger, apache and MySQL. I am moving this to Amazon AWS with the following simple setup:
ELB > Web Server > MySQL
Lets say I am expecting a huge spike in daily users and want to start to scale this out on Amazon AWS using multiple instances. Where does a newbie start on this journey? Do I simply create an AMI from my production configured web server and get the ASG to launch these when required?
I understand that AWS increases the number of instances using auto scale groups as the load demands it, but do I need to architect anything differently in my Rails application for it to run at scale across multiple interfaces?
The problem with scaling horizontally is that it really depends on the application. There's no "just-add-water" ways to do it.
But there are some generic recipes you can follow in the beginning:
Extract MySQL server into a separate instance, which is capable of holding a higher load. Then create as many worker (i.e. app) instances that connect to the MySQL database as you need. You can keep doing so before your MySQL server gets saturated with requests, and can no longer keep up with the load.
When you're done with step 1, you can add MySQL replicas and setup a master-slave replication. This will leave you with a MySQL cluster, where one server can accept writes and all the others are read-only. After your set it up, change your application to send SELECT's to read-only replicas and INSERT/DELETE/UPDATE's to the writeable master server. This approach is based on the fact that most of the applications do reads way more often than writes. It can be not the case for you, but if it is, it'll keep your afloat pretty long. Right before you saturate MySQL master server write performance.
Once you've squeezed everything from step 2, you can go ahead and shard the data. This is now becoming more and more dependent on your application. But I will provide a blind example in order to convey the idea. Say, you have a user-centric application (e.g. a private photo-album, with no sharing capabilities), and each user has a name. In this case you can make two completely independent clusters, where the first one will serve users with names starting A-M, and the second one will serve ones with N-Z. It essentially makes the load twice as less, but complicates the whole architecture.
Though generic, these recipes can help you build a pretty solid application capable of serving millions of users daily before you're forced to bring up more exotic ways of scaling.
Hope this helps!
Related
I've been running a Rails app on 1 big dedicated server. Now for scaling I want to switch to a cloud service hoster and serve the app on 3 instances - App, DB and Redis.
I have really bad experience with Heroku performance wise and hence cost efficiency. So for me 2 Alternatives remain: Engineyard and Enterprise-Rails.
What I find important is that Engineyard doesn't offer an autoscaling option to handle peaks. On the other hand Enterprise-Rails doesn't have too much of documentation, most of it is handled by a support crew which is setting up everything.
What are other differences and what should I use for my website? I don't need much of administration work and I am not experienced with it. Basically I just want my Site to run optimally safe, stable and cost efficient without much personal work involved.
I am running a massive Rails app off AWS at this time and I'm really happy with it. Previously I had a number of dedicated boxes that were always causing problems - sooner or later one of them would crash for some reason, Raid failures, database problems whatnot.
At AWS I use RDS for database, elastic cache for caching, I keep all my code on a fat instance that acts as staging server and get a variable number of reserved instances to load the code via NFS.
I also use autoscaling - we've prepaid for a number of reserved instances and autoscaling helps starting up nodes when CPU usage goes above 60%, then removing them when it goes below 25%. autoscaling rules are based on cloudwatch alerts that can be set to monitor a particular group of instances, memcache servers, and so on, you even get e-mails and SMS notifications via SNS when certain scaling activities take place, say when more than 100 instances are spammed in less than 1 hour (massive traffic spike). The instances also get added right up to the load balancers by the way and you don't need to mess with the session store as you can use the sticky session feature which is quite nice.
Recently I also started using a 2nd launch group with spot instances, this complicated things a bit in terms of cloudwatch rules but I'm able to save a lot every month as spot prices are much lower. When the spot price (minimum) I bid is not enough, the set-up I have switches back to reserved instances.
Even more recently I've also started using CloudFront which got my app's page assets to load real fast (about 2 megs of CSS, JS, some icon sprites). Previously I was serving directly from instances via the load balancers.
This took about 20 hours to deploy, test and tune for maximum performance and availability.
One of the problems I have with AWS is that there's no support unless you're prepared to foot a bill. They claim some support is offered without a subscription but the only option in the support area is Billing. Ha. Fortunately it's all stable enough not to put me in a position where I'd have to pay for it.
Overall Rails fits in quite nice with AWS. I spend less than 2 hours per month doing maintenance, where I was spending over 30 previously. Most important for me is that I know that I can GTFO on a vacation for X months knowing nothing will cause any trouble - haven't had a monitoring alert more than a year.
Later edit: the app is a sports site with white labeling feature, lots of users, lots of administrators working on content in the back-end, database intensive as we show market pricing data that should update every few seconds. I had an average load time of about 3 seconds per page with dedicated servers that were doing about the same thing - database, memcache, storage, load balancing, web app. Now my average is under 1 second. Monthly bill is about 8 times lower now.
While Engine Yard doesn't offer auto-scaling (it is in the pipeline), we do have a fairly easy to use scaling feature that allows you to spin up multiple instances at once in times of need.
The advantages over something like Enterprise-Rails is the full documentation, the choice to deploy from the CLI or the dashboard,and our amazing support team. It's also easier to use Engine Yard and move from a personal machine or from another cloud setup than it is using a service such as AWS directly.
I am currently using an AWS micro instance as a web server for a website that allows users to upload photos. Two questions:
1) When looking at my CloudWatch metrics, I have recently noticed CPU spikes, the website receives very little traffic at the moment, but becomes utterly unusable during these spikes. These spikes can last several hours and resetting the server does not eliminate the spikes.
2) Although seemingly unrelated, whenever I post a link of my website on Twitter, the server crashes (i.e.,Error Establishing a Database Connection). Once restarting Apache and MySQL, the website returns to normal functionality.
My only guess would be that the issue is somehow the result of deficiencies with the micro instance. Unfortunately, when I upgraded to the small instance, the site was actually slower due to fact that the micro instances can have two EC2 compute units.
Any suggestions?
If you want to stay in the free tier of AWS (micro instance), you should off load as much as possible away from your EC2 instance.
I would suggest you to upload the images directly to S3 instead of going through your web server (see some example for it here: http://aws.amazon.com/articles/1434).
S3 can also be used to serve most of your web pages (images, js, css...), instead of your weak web server. You can also add these files in S3 as origin to Amazon CloudFront (CDN) distribution to improve your application performance.
Another service that can help you in off loading the work is SQS (Simple Queue Service). Instead of working with online requests from users, you can send some requests (upload done, for example) as a message to SQS and have your reader process these messages on its own pace. This is good way to handel momentary load cause by several users working simultaneously with your service.
Another service is DynamoDB (managed NoSQL DB service). You can put on dynamoDB most of your current MySQL data and queries. Amazon DynamoDB also has a free tier that you can enjoy.
With the combination of the above, you can have your micro instance handling the few remaining dynamic pages until you need to scale your service with your growing success.
Wait… I'm sorry. Did you say you were running both Apache and MySQL Server on a micro instance?
First of all, that's never a good idea. Secondly, as documented, micros have low I/O and can only burst to 2 ECUs.
If you want to continue using a resource-constrained micro instance, you need to (a) put MySQL somewhere else, and (b) use something like Nginx instead of Apache as it requires far fewer resources to run. Otherwise, you should seriously consider sizing up to something larger.
I had the same issue: As far as I understand the problem is that AWS will slow you down when you reach a predefined usage. This means that they allow for a small burst but after that things will become horribly slow.
You can test that by logging in and doing something. If you use the CPU for a couple of seconds then the whole box will become extremely slow. After that you'll have to wait without doing anything at all to get things back to "normal".
That was the main reason I went for VPS instead of AWS.
I'm about to start development on a project with very uncertain load/traffic specifics. When it will be released there will certainly be very low load that can easily be handled by a single desktop quad code machine.
The problem is that there will be (after some invite-only period) a strong publicity for the product so I expect considerable traffic/load peaks.
I haven't read enough about cloud providers and I'm mostly leaning toward Amazon or Azure for the credibility these two companies have without checking them out as I should with others (ie. Rackspace that I suppose is also a cloud service provider).
What I want
I would like to create a normal Asp.net MVC web application that can be run on in-house single machine low-cost server. It would run web server along with database (relational and maybe also document) and fulltext search (not SQL FTS but rather high speed separate product like Lucene or Sphinx). But after initial invite-only period I'd like to move this app to the cloud to make it more traffic/load demand-friendly.
As much as I know Amazon offers a sort of virtual machine hosting which I understand you setup as a normal server but has possible flexible resources in terms of load power. I'm not sure if that can be accomplished on Azure as well.
Questions
What is your experience with application transition to cloud and which one did you choose and why?
What would you recommend I should think about when designing/developing the solution to make the transition as painless as possible.
Based on your experience is it better to move to the cloud (financial wise) or is it better to buy your own servers and load balance application yourself and maybe save money on the long run?
"Cloud" is such a vague term. Still, I think this is a very good question.
Basically, IaaS cloud hosting does not magically make your application scale. It's really a virtual private server with very short contract / cancellation periods.
For scalability, the magic lies not so much in the hosting, but in the horizontal scalability of the application code itself. This is related to all the distributed computing challenges. For example, adding more application servers is not always easy: you must be sure that you don't persist any user state in the server application (but rather in a database, static can be evil), caching can be problematic because local caches can make the situation worse if you're using a round-robin strategy, etc.
What is your experience with application transition to cloud and which one did you choose and why?
What would you recommend I should think about when designing/developing the solution to make the transition as painless as possible.
You don't really have to do anything different just to host on EC2 or Azure -- basically. But of course, it's not that easy when things grow.
For instance, EC2 instance storage is rather limited. Additional storage on EBS, however, does not provide comparable performance characteristics and can be a bit more laggy than a disk. The point here is that EBS does magically scale, and it's probably more PaaS than IaaS; but it's not a simple hard disk and it does, consequently, not behave like a hard drive. I don't know about Azure block storage. In general, expect additional abstraction layers to introduce problems of their own, no matter what they do.
Based on your experience is it better to move to the cloud (financial wise) or is it better to buy your own servers and load balance application yourself and maybe save money on the long run?
Typical cloud providers are more expensive than the usual 'round-the-corner VPS providers, but they are, to my experience, also much more reliable and professional. EC2 has a free tier (but it's quite small), Azure gives you a small instance for free for 3 months.
Doing the calculation right is rather tricky; for example, if you have to shut down your service for whatever reason, it's nice to be able to cancel now rather than pay another year - you might want to put this risk into your calculation. On the other hand, both EC2 and Azure will be considerably cheaper if you sign up for 6 or 12 months, rather than paying by the hour.
You might want to check out the free Azure plan, because it's nice to start fiddling around without any cost. A big advantage of cloud providers is that you can scale vertically very easily: buying a 16 core, 64GB RAM server machine is really expensive, but if there's so much traffic on your site, upgrading your plan won't be such a big issue.
As someone hasn't mention it yet...
AppHarbor has been amazing. You can push stuff in a matter of minutes. Deployment is a breeze. And setting up your project for it is easier as well. And it doesn't even require any major changes in your solution to fit in.
For the full-text search, you might consider something like Websolr.
A lot of this depends on what your app is doing (e.g., are there separable components that might benefit from running on different instances, vs. a simple CRUD application with a front end). One thing to consider is that in a cloud application you normally don't have a traditional relational database. As such, you have to choose either cloud or traditional hosting, or plan on coding your access layer twice. Azure does have relational databases (SQL Azure), although they're not identical to SQL Server 2008R2. You're going to have to research the pros/cons of a cloud setup for your specific situation.
As far as financial concerns, it's usually a lot cheaper to just get an account with a hosting company instead of a cloud service, since you pay by the month, instead of the hour (last time I checked an account with Azure running 24/7 for a month would cost about $40-$50, while you can get hosting for $15 a month). The savings with the cloud come in when you have to run several servers, and the cost of maintaining them surpasses the cost of the instance on the cloud platform.
So, sorry, there's no silver bullet answer for you. Read up on the different services available. Consider what your application needs, what prices will be, and go from there.
I have just migrated an MVC-based application from a dedicated server to Azure. When migrating the MSSQl-database, I first tried importing .bacpak files but some of the tables failed because of their size. I then used the SQL Database migratio wizard which worked fine for small tables but failed for tables with BLOB-fields. For these tables I had to use temporary intermediate tables. Then after a while after all the data was transferred setting up the Webapp was a breeze and we went in production. At first, everything seemed to work just fine, but after a couple of hours when the load got heavier, all kind of errors occurred. I went into the Azure portal and it was really easy to see the
I am creating a Grails application that is the backend for a mobile application. It is currently deployed on Amazon EC2. It persists data to a mysql database. One instance currently pointing to the database. I plan to deploy multiple instances of the app behind a load balancer and eventually have read requests go to slave instances of the db. We plan to release in the coming months and have a beta group of a couple of thousand users. It is more read intensive than write.
We have looked into using mongodb instead of sql and see it as a good solution.
Not having a lot of experience scaling mysql ( or mongodb ) would it be easier to scale mongodb since it has features such as auto sharding. ( Looking for thoughts from people who have done both ) I am of thinking it will be easier to switch to mongodb now rather than be in 'production' and having to migrate.
Thoughts?
MongoDB has two versions of "scaling":
Read scaling via replica sets.
Write scaling via sharding.
They're not silver bullets, but they're both very easy to set up. Replica sets have auto-failover which is practically essential when using EC2 (they have a good history of just randomly failing nodes). When you need write scaling, MongoDB has documented processes for upgrading your replica set to a series of sharded replica sets.
The unfortunate limitation is that (last I checked), things like scalr don't really support automatic scaling. So you'll have to roll your own solution for adding and removing nodes from the set.
Some important considerations:
Disk IO performance is sketchy in the cloud. Good performance is all about the amount of RAM you can throw at the problem.
If you're using replica sets for reads, ensure that your driver / data wrapper is capable of handling the distribution of reads. Just like MySQL it's not currently "free", you'll need to decide "write vs. read".
64-bit machines. MongoDB really wants to operate on 64-bit hardware. This is a cost consdieration as you'll probably have to ramp up with 4GB machines instead of 2GB machines (I don't think this is a big limitation, but I also know what it's like to be a startup).
MongoDB is still new tech. The lists are very active, and people are using it in production for very large data sets. But this is still a new product, you have to be prepared to work from the command-line and parse through docs and ask questions.
would it be easier to scale mongodb
At some level scaling is going to be a "hard" problem. What MongoDB does well is provide a way to really scale out lots of boxes horizontally with replication. In my experience, MySQL really tops out at around two boxes for writes. You can easily configure co-masters, but after that you have to start mucking around with all kinds of partitioning and you basically lose the ability to do joins.
I am of thinking it will be easier to switch to mongodb now rather than be in 'production'
It probably will.
Thoughts?
Start small. Get one piece working and see if you like how it works. If you have access to an EC2 account, then it's easy to spin up a couple of machines and play. MongoDB is not a panacea, but it works really well for a lot of modern web problems. Just measure how badly you need joins :)
Given that each Ruby-On-Rails application needs at least about 40MBs of memory, I was wondering if there is a way of running multiple rails-application instances (different ones) over one interpreter of Ruby so that all shared libraries (rmagick etc) are shared between different application instances, saving space.
If that would be possible, then, I could be running 5-6 rails applications in a single 256RAM virtual server.
Is that possible?
I don't think this is possible without substantially changing the current code base.
But all is not lost.
If these websites are fairly low traffic and you have a fast vps you should take in mind that mod passenger drops the instances from memory if they're inactive for a while. So in theory you could run an unlimited amount of applications as long as you only have a few active at the same time. The price is a slower response on the first request that loads the instance.
Another option would be to load all the shared libraries, then fork off as many child processes as you have apps (use Process.fork) and run a different app in each child.
Pages of memory which are only read and not written will be shared between the parent and child processes.