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When Should You NOT Use Rails?

   A chimpanzee in a white coat types at a keyboard lit by glowing LEDs.
   He's gorgeous, yes. But is his talent natural… or is it Ruby on Rails?

   I was [8]recently on Jason Swett’s podcast again. He’s a great
   interviewer and I always have fun with him.

   By Twitter request we talked about… When would you not use Rails? It’s
   a great question.

   For the entertaining version, [9]listen to the podcast. For the
   just-the-facts extra-complete version, I’m writing this post.

When Is Rails the Wrong Choice?

   I’ll start with a few simple, obvious times you wouldn’t use Rails, and
   then I’ll talk about some technically interesting times.

   First, and most important, is team familiarity. If your team doesn’t
   already know Rails and isn’t especially interested in learning it then
   Rails is the wrong choice. This should be obvious, but it still
   deserves first billing.

   Second, when you know some other framework fits better. I’ll talk more
   below about when that is. But sometimes you have a specific concern
   that trumps everything else. If you need to use a Java-language machine
   learning library and you don’t want to use JRuby for some reason, Rails
   isn’t your framework. If you’re writing a WordPress plugin, you’ll be
   doing it in PHP. Often there’s one specific compatibility concern that
   overrides everything else.

   You can also think of it as: use it where Rails’ good points hold and
   its bad points don’t. So we’ll also talk about the good and bad points.

   Separately: you’d normally only use Rails as an HTTP server, so some
   tasks just aren’t Rails-shaped.

When is Rails Too Much?

   [10]A pirate puppet with an eyepatch, safety goggles and a huge
   scraggly mustache watches over a purple crystal ball at his feet.' He’s
   too much lab assistant for your lab.

   Some places not to use Rails can include:

   Really Small Tasks that Won’t Grow: if a server does very little, Rails
   is often too much. Not going to touch a database? Then the DB setup
   isn’t helping you, is it? Just a tiny low-traffic intermediate server
   with no caching? A lot of Rails is more trouble than it’s worth.

   Be careful with tasks that grow, though — making a tiny server scale up
   to do a lot more can be ugly. If you’re already serving HTTP pages to a
   human with a web browser, consider that you may have to add features to
   it later. Something like that is already fairly large from the word
   “go”.

   When It’s ‘Just’ an API Server: Rails has less to offer an API server
   that speaks JSON over the wire. A lot of its HTTP security doesn’t
   matter for that case: CSRF protection is entirely about dealing with
   HTML and Javascript. Many kinds of XSS attacks are dependent on a
   browser as the weak link, or on putting unescaped user input into HTML.
   Redirection vulnerabilities assume automatic redirection, which APIs
   usually don’t do. You can prevent SQL injection attacks with just an
   ORM, a simpler ORM, or even the raw Ruby MySQL and Postgres gems, which
   support question-mark arguments.

   Rails security really shines when you’re navigating the bewildering
   world of HTML and browser security. Small projects that mostly speak a
   structured format read by machines will get less from Rails. Securing
   something like an integer ID or a hash of strings is just easier than
   ensuring your HTML contains no script tags or anything exploitable.

   Related to that is when you’re doing in-browser rendering and Rails is
   ‘just’ serving JSON. It’s a weird kind of in-between case. A lot of
   Rails security and convenience functions no longer help you, but you’re
   still doing things where internal libraries (ActiveRecord, ActiveJob,
   ActionMailer) can be highly useful. But if you’re never rendering HTML
   on the server and you’re very sure you never will, Rails will probably
   help you less.

When Is Rails Not Enough?

   Rails is also designed for a small team and a medium-sized codebase. A
   huge team (lots of programmers) or a huge codebase (lots of
   controllers, models and/or lines of code) will tend to drag down the
   standard Rails-app structure.

   Ruby allows for a lot of [11]non-local effects. Whether that’s
   monkeypatching, writing to a database or creating new types at runtime,
   Ruby isn’t designed for a team of 200 programmers where you don’t trust
   some of them. There are too many ways for them to cause you trouble.
   You can use [12]good tooling to scale Ruby to larger teams, but even
   that will [13]tend to have exceptions and difficulties. That’s not
   really Ruby’s sweet spot.

   In most cases you can cut up a large project into smaller projects. If
   one Rails app is too big, you can often separate it into multiple apps,
   or a thinner app with more back-end services, or an app and a separate
   microservice, or… One way or another there is usually a way to separate
   out smaller pieces. Ruby strongly encourages that, as do I.

   There are also not-quite-Rails structures that can scale better. Avdi
   Grimm’s (now retired) [14]Objects on Rails was an attempt in that
   direction, as is [15]the Hexagonal architecture for Rails, which in
   turn has a lot in common with the older and more general [16]N-tier
   architecture.

   But at some point you might want to consider a different framework.
   [17]Hanami is an obvious choice, designed to be less quick and nimble
   than Rails for getting a tiny app off the ground, but more scalable if
   you want to use the same code with a lot more contributors.

   I’d still start out in Rails, personally. If you’re building something
   quickly to see if anybody cares, I know of no framework that comes
   close to its productivity. Wait to rewrite (in a more rigid framework)
   until you’re successful and you can afford the drag on your development
   speed.

   The other worry here can be performance. If you’re rewriting a project
   that is already as large as the current Basecamp… then you’re
   [18]actually fine for performance. Rails still scales great for them.
   But if you’re looking at something a hundred times larger (which by
   definition means B2C, not B2B) then you might have a situation where
   your server costs are substantially greater than your engineering
   payroll. In that case it can make sense to slow down your engineers to
   pay lower server costs. To check this, see what your EC2-or-equivalent
   costs are just for your application servers, which are what run Rails.
   And check your payroll just for web engineers, which is who writes in
   Rails. Normally the engineering payroll is much larger and you should
   stick with trading cheap machine time for expensive engineering time.
   But at some point the balance may tip and you should consider raising
   your engineering payroll to cut your server costs.

When Does Rails Have the Wrong Assumptions?

   [19]A pirate, a bear and a chimp sit at a wicker table. The bear looks
   into a very old-fashioned microscope as the other two look on. They’re
   checking the microscope for real-world use cases where Rails might be
   wrong.

   Before checking if Rails’ assumptions are right for you, we should see
   what those assumptions actually are.

   Before you take my word for it, I recommend taking [20]David Heinemeier
   Hansson’s word for it in the form of The Rails Doctrine. It’s a great
   document and it covers a lot of ground.

   Indeed, if you want to better understand why Rails isn’t amazing for
   large, low-trust teams, you should read [21]“Provide Sharp Knives” in
   the Rails Doctrine several times. A lot of Rails’ tradeoffs are
   entirely by design.

   Rails also has some simpler assumptions: it assumes you’re writing an
   interactive app with server-rendered HTML. It assumes that security is
   vital (Rails trades a lot for security) but that you don’t want to
   build your own custom security system in most cases. And it assumes
   that you either have a small, excellent team doing prototyping work
   (“Provide Sharp Knives”) or that you have a possibly-mediocre team that
   needs powerful built-in guidelines ([22]“The Menu is Omakase.”)

   Rails also assumes you want high developer velocity at a cost of
   technical debt. In other words, it’s designed for building very
   quickly. That makes sense when technical execution is not your biggest
   risk. For instance: if you’re building a small startup, and you’re
   pretty sure you can build the site but people may not buy your product,
   you are dominated by market risk. That’s when Rails is perfect. You
   want to build very quickly. And even if you build perfectly, you’re
   probably going to have to throw away the result for nontechnical
   reasons, like “people don’t want to buy it.”

   As part of “high dev velocity, technical debt is okay” Rails assumes
   things like, “you’ll want to use a lot of gems” and “dependencies that
   work are fine if they speed you up.”

   Rails assumes you don’t mind scaling out application servers
   horizontally (by bringing more of them online.) It’s designed to scale
   well if you can do that. Rails assumes CPU is fairly cheap and it’s
   usually right about that. Relatedly, Rails assumes that the database is
   usually your most serious performance bottleneck, which is how web
   applications usually work.

   Rails also assumes you’ll have some calculation or data transformation
   in your application. It assumes that it’s okay to use some CPU because
   you’ll be doing that anyway.

   (When does that last assumption matter? Let’s talk about Evented
   Servers and see.)

What Isn’t Rails Good At?

   [23]The Node.js logo. Sometimes you need it, or something like it.

   While Rails is great at a lot of things, there’s one particular task
   that it’s not amazing for: shim servers.

   By “shim servers” I mean servers that do very little calculation but
   integrate answers from a few other back-end services and relay the
   result. Imagine a server that queries two JSON services and combines
   the result with simple string-manipulation, for instance. It does very
   little calculation, but it juggles a lot of events.

   And that’s the relevant word: “events.”

   There is a specific kind of app architecture embodied by Node.js and
   its relatives called “Evented” programming. It can support many
   thousands, or even millions, of simultaneous connections with a tiny
   amount of server resources. It can be both high-throughput and
   low-latency. Its benchmark numbers are matchless… for the cases where
   it works.

   Rails can’t match Evented programming at what Evented programming is
   good at. Basically no framework can. There are Evented frameworks for
   Ruby (e.g. [24]EventMachine, [25]Async.) Rails is built differently.

   If Evented is so much better, why don’t we use it for everything?
   Because it doesn’t work for everything. I emphasise calculation
   per-request because an Evented server will fall down and die if you try
   to make it do very much calculation per-request. Having one server
   handle a million connections is no good if each connection winds up
   using a hundred milliseconds of CPU time — that’s simply too many
   connections and the latency will be terrible.

   In other words, Rails and Node.js are different tools for different
   projects. If you’re thinking, “I should either use Rails or Node for
   this” I would recommend looking deeper into your project (and/or your
   framework) until it’s obvious which one is the right answer. They do
   different things.

Look, I Just Scroll to the Bottom for the Summary and Criticise It On Reddit

   [26]A chimpanzee in a lab coat stares down at his lap, containing
   sections of wooden train track, and his hand holding a toy train. I’m
   sure this is the right answer, but I have forgotten the question.

   Rails is the wrong choice if your team doesn’t want to use it or
   doesn’t know how.

   Rails is the wrong choice in cases where a different framework is
   specifically better, or you have a specific library you need to be
   compatible with that isn’t Rails-friendly.

   Rails might be the wrong choice if you’re not rendering HTML on the
   server, especially if your project is very small and/or doesn’t use a
   database.

   Rails is the wrong choice is you’re not doing prototyping-flavoured
   work, preferably with a small, highly-competent team.

   Rails is the wrong choice if your dev team or your app code is too big
   and you can’t subdivide the project.

   Rails is the wrong choice if your project wants an Evented server like
   Node.js or EventMachine.

   This article is the wrong choice if you’d rather [27]listen to an
   entertaining podcast on the same topic.

   If you’re wondering when Rails is the right choice, [28]the Rails
   Doctrine is a great first step.
   Aug 6 2020
   [29]ruby [30]rails

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