The Minimum Viable Rails Stack, Now Reddit Frontpage Approved | Hacker News Reader

The Minimum Viable Rails Stack, Now Reddit Frontpage Approved

goodfil.ms

136 pointsjohnb41 comments

This is almost exactly how I deployed NameTerrific (https://www.nameterrific.com). It automatically gets ready for any horizontal scaling in the future.

In addition, I allocate the workers to their own instances so that they can grow independently. Also I use Capistrano to automate deployment. Whenever additional resources are needed, simply clone the instance and add it to the load balancer.

I use 2 Nginx workers and 8 Unicorn workers in a single app instance, and they serve in HTTP at 80 and 443 (yes they respond in HTTP via port 443 and the app should assume it's HTTPS). The app instances are firewalled in a private network and they use private IP addresses.

The load balancer has two networking interfaces, one public-facing and one private-facing. It's basically a reverse proxy serving traffic in both HTTP and HTTPS (which will be forwarded to HTTP:443). So the load balancer handles the encryption entirely.

The assets get compiled during deployment, and everything gets cached. I bundle all the CSS and JS into a single package, so that there's nothing to load other than the HTML and images (natively async) in subsequent visits. The website is simply way more responsive when deployed this way. I also use CloudFront to host the assets by simply pointing the cloud distribution to the website itself as the origin. Rails will handle the assets host automatically as well.

Whenever I need to deploy or manage the database directly for any reason, I will need to connect to the private network via VPN. It's secure and just neat.

If I need to build a local mirror, I'll install another nginx box, connect to the VPN, and reverse proxy HTTPS requests to the HTTP:443 directly. This reduces the HTTPS handshaking latency while still maintaining the security. And it just works.

EDIT: Added a link to make it easier for the curious people.

If you don't mind me asking, what load balancer are you using? I'm trying to setup multiple app servers on EC2 behind ELB using Redis as a session_store and I can't get sessions to persist.

I used to use ELB, but later I migrated the whole app to a self-hosted private cloud on a dedicated server.

I'm using Nginx as the load balancer, and there're no session problems for me because I use the built-in secure cookie store.

Thanks for the response. I appreciate it.

This sounds like a bug in your session store code as opposed to a load balancing issue. Are they all on the same host name?

> Uses MySQL or Postgres as the datastore, deployed to a single instance, with frequent data backups to cloud storage

this does not seem to be "ready for horizontal scaling in the future".

I don't know whether you have multiple slaves, and TFA itself says that they'd scale the database _vertically_, I'm just stating that there's a pretty important mismatch between what you say and what the article says.

Well, it's true that database isn't horizontal-scaling-ready as described in the OP. But for many web apps, the database is not the bottleneck. Efforts should be spent on memory caching and NoSQL long before vertical scaling generates diminishing returns.

Of course, it's easy to add a master-slave replication to a single database instance when the need arises, even possible without downtime. So I assume most RDBMSs to be horizontal-scaling-ready.

The difficult part is the app stack. We need to be able to deploy more instances in minutes, not hours or days. If at the beginning we cram everything (Nginx, Unicorn and MySQL) into a single dedicated server it can be really difficult to increase the capacity in the future without downtime or additional expense. Instead, even if you don't need the power of several dedicated servers, it's worthwhile to virtualize a single server and split into a few boxes and make them horizontal-scaling-ready. Then you can clone, resize and migrate the instances.

This is what I do to increase the capacity of my app in a few minutes:

  1. Create a new instance, and load the pre-built app image
  2. Assign an IP address and add it to the DNS (like app-3.nameterrific.net pointing to an internal IP)
  3. Add the app server to deploy.rb (for Capistrano)
  4. cap deploy
  5. Add the IP to load balancer

That's it. This stack can be used from day one affordably and it can scale to potentially billions of visitors.

>But for many web apps, the database is not the bottleneck.

Really? I think the database is usually the bottleneck in most web apps. That's why you cache data: to avoid hitting the database.

Writes to the DB (and more importantly replication since it is single threaded in mysql) are often the bottleneck that is hard to scale. Write through caches can scale reads up very high. It takes a long time to hit the write limit for most applications so often read slaves and memcache is sufficient.

"We didn’t have any page caching in place at all."

Cache me if you can! If you're a high-traffic site and you are not caching static content (I recommend Varnish highly), then your are throwing money or good user experience out the window.

*you're

And I agree completely. Varnish is goddamn magical and a fascinating exercise in a principled approach to kernel-oriented memory management (a mindset I don't normally undertake).

Part of Rails 4.0 will be further pushing the "Russian Doll" caching that 37signals/DHH talks about here: http://37signals.com/svn/posts/3112-how-basecamp-next-got-to...

One of the great things I love about Rails 3 is how easy it is to start caching. It can, and does, cause issues so make sure you're including caching in your test suite. I'm definitely looking forward to seeing how Rails 4 pushes this forward.

When you say static content, do you mean actual static content, or dynamic-but-still-kind-of-static? Actual static content like CSS files and background images doesn't get any benefit from varnish. Something like the HN front page, where it is dynamic but consistent for all users at a specific point in time, is what you need to put behind varnish.

In high traffic caching css and images in varnish as well makes sense as it is much faster at evaluating and responding to the HTTP request than say Apache which will be busy building dynamic requests.

Not really the case if you are using Nginx though.

Both. Varnish defaults to caching jpg,gif,png,css,etc. but we also having it caching things that are pulled from the db and processed. So it leaves our cpu-intensive backend untouched for the vast majority of requests.

The key thing I got a bit wrong was high-traffic mostly static "content", vs high-traffic "very custom" which is a) what I was used to at envato and b) what I thought we had on our hands at goodfilms.

I think in a growing site with a lot of custom per-user content (like a social network) the extra complexity of a cache layer and managing expiry is more pain than it's worth while iterating the product quickly. If you're mostly a content site, it's definitely the #1 thing you should be doing.

Realising that we're both at the same time, depending on the user or page, means that sometimes the cache stuff is the right thing to do, and sometimes not. I was leaning too far towards not, and happy now with the balance we've picked.

Absolutely. At theconversation.edu.au we run a content site—we publish the news, which is the same for everyone. This means we can cache the front page and all the articles as static HTML, and then annotate the page with user info for signed-in commenters, editorial controls for signed-in editors, and so on.

(We have a separate cookie that is present for signed-in users, so the fronted knows whether it should fire the annotation request.)

The result is that we can serve a sudden influx of unauthenticated users (e.g. from Google News or StumbleUpon) from nginx alone, which gives us massive scale from very little hardware. It's likely that the network is actually the bottleneck in this case, and not nginx.

Interested in what you mean by annotating the page after caching it, do you have any more info on this?

The cached page contains content suitable for everyone, so it looks the the user is logged out.

An extra AJAX request grabs the users logged in status, CSRF token and similar data as JSON and then modifies the page so the user sees what they expect (a logout button, a comment form, etc).

Doesn't that cause content movement?

Essentially talking about edge side includes [http://en.wikipedia.org/wiki/Edge_Side_Includes].

More about ESI http://i.imgur.com/KNvg0.jpg From a slidedeck presentation here http://lanyrd.com/2012/codeigniter-conference-us/coverage/?c...

If you're running Ruby on Rails record cache will do it all for you (I've yet to run into any issues, the one I thought was an issue was actually a pgpool-II bug).

https://github.com/orslumen/record-cache

If you're on Django I think cache-machine does the same thing. There are some things you won't get cached this way that you could manually (functions and procedures), but I think they're both conservative enough that you won't return stale resources.

Great post, it is great to see startups being open about how they architect their systems and overcome issues with scaling.

This sort of information helps people building the next group of startups save both time and money.

Keep up the great work!

Well done guys, keep scaling and keep representing the Melbourne tech scene!

We used New Relic for a while with Heroku but turned it off because of a number of performance and stability issues we seemed to be seeing with it. In particular application boot times (for the first requests anyways) seemed to be negatively affected.

While the "webscale" method with nginx you detailed is nice [1], why not use Varnish or nginx's built in proxy_cache features [2]?

[1] https://gist.github.com/3711251

[2] http://wiki.nginx.org/HttpProxyModule#proxy_cache

Nice post, but:

Don't self-back-pat.

It read more like marketing for the company than anything of much worth.

Don't use the words "web scale".

It is a meaningless term. How many requests per second and how many guest and user sessions for how long of a time is "web scale"? Does "web scale" just mean Christmas shopping traffic on your crappy e-commerce site that no one visits, does it mean you can survive being top link on HN on a Friday morning, or slashdotted, or DoS attacked by anonymous, or survive a fucking flood and the data center lifts off the ground and enough flexibility and strength in the trunk lines to handle a tsunami?

Don't just throw users at it.

Unless testing is very costly and you need every user's eyes on your untested code as possible, that is just stupid. Look at Tsung, Grinder or JMeter, or the many other ways you could generate load as a first step before you do that.

Don't gloss over the details.

Sure you said you were using Rails 3.2 and postgres and a tad bit about the architecture, but who in the hell doesn't know that you need to load balance, need to put the DB servers on different VMs/servers than the apps. Although- having everything on both and some stuff just not turned on and live is not a bad idea for emergency fault tolerance, and you didn't mention that.

Your caps-lock key appears to be broken.

Oh, you're right- thanks! Just fixed the comment. I'll get the capslock key fixed on Monday.

A few questions:

1. Is it possible to spin up two apps on Heroku? 2. What load balancers are available with the above? 3. Anyone have a link to a run down of how to back up your Postgres DB periodically?

Thanks

To answer my own question, there is a free addon called pgbackups that will do this for you, and Heroku automatically load balances between dynos.

Pgbackups is not for load balancing. That is already automatic. Pgbackups is for managing Postgres backups.

3. Anyone have a link to a run down of how to back up your Postgres DB periodically?

"Pgbackups" answered this question.

For 1 and 2: AFAIK Heroku already has three layers, the Nginx routing mesh, Varnish cache and your dynos. Everything is already handled for you so if you have two dynos, the traffic will rotate between the two. You don't need a load balancer for Heroku. It's built-in.

Note: Varnish isn't available on the (standard) Cedar stack. Here's how Heroku suggests you approach cacheing:

https://devcenter.heroku.com/articles/http-caching

It's possible to run multiple server processes of a single Rails application on a single Heroku worker to gain some additional concurrency capacity, obviously with some caveats and limitations:

http://michaelvanrooijen.com/articles/2011/06/01-more-concur...

Great job! Can you do such page for EC2 too?

Engine Yard Cloud does a lot of this out of the box on EC2 while still affording root access. There is a price premium obviously.

we have pretty much used a similar stack in websketch.com

Reply on news.ycombinator.com