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Question

I'm looking for some advice here. My school's student section registration process is online and involves around 6,000 students

They base seating off first come first serve basis. Every year they open the site at noon and floods of people get on a try to register as fast as possible to get good seats. Every year without fail the server crashes and everyone is mad.

After several years of being frustrated myself, I've offered to redo their registration system.

My plan is to rewrite it in ruby on rails, and use heroku for hosting.

• Does a heroku dyno only handle one request at a time?
• Heroku scales up to 50 dynos. Will that be enough to handle around 6,000 users with about 5 pageviews per transaction in a short amount of time, say a half hour?
• Any helpful strategies or tips you can give me before I dive into this project?

Answer 1

Does a heroku dyno only handle one request at a time?

Yes. Heroku dynos are single threaded.

Heroku scales up to 50 dynos. Will that be enough to handle around 6,000 users with about 5 pageviews per transaction in a short amount of time, say a half hour?

This depends on how fast your page loads. For arguments sake let's pretend it takes 2s per page request (as per Google Analytics recommendation) and you need to load 6,000 users x 5 page views / 30 minutes - 1000 page views per minute.

At 2s per page load, one single dyno would load 30 page views per minute. At 50 dynos, this would be 1500 page views per minute. This would obviously allow you to exceed your overall goal and leave you some room for error, but if all 6000 users are hitting the page at once then a single Heroku app may not be able to keep up depending on your timeout. You would need to implement a user queue system - explained below.

Any helpful strategies or tips you can give me before I dive into this project?

All that said, a 2s load time may vary depending on the assets your page needs to load, the amount it needs to interact with a database, it's queries, caching, etc. Your page can also potentially serve much faster.

You also need to worry about the initial hit of all the users. This could be taken care of via a first come first serve queue system - similar to that used by Ticketmaster if you've ever used their site. This could be accomplished via AWS SQS or your preference of queue system.

With a user queue and caching of your assets and common database queries, you should be able to accomplish this with 50 or less dynos.

EDIT: I'm taking your word for it that Heroku will run 50 web dynos. They show 24 as max on their pricing page, but I cannot find any info one way or another.

Answer 2

Does a heroku dyno only handle one request at a time?

It depends on web server you use ( https://devcenter.heroku.com/articles/dynos#dynos-and-requests ). If you want more concurrency within a dyno, I'd suggest taking a look at something like Puma .

Heroku scales up to 50 dynos. Will that be enough to handle around 6,000 users with about 5 pageviews per transaction in a short amount of time, say a half hour? Any helpful strategies or tips you can give me before I dive into this project?

You can have more than 50 dynos. A specific answer for you app is going to be way better that a guess or generalization. Run a load test against your site (eg, using Blitz ) and find out the real numbers. Costs for add-ons are pro-rated per second, so you only pay for the period you have it installed. So make sure you uninstall or downgrade Blitz once you've finished your test.