Grisha Trubetskoy

Notes to self.

Building a Go Web App in 2017

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Update: part 2 is here, enjoy. And part 3. And part 4.

A few weeks ago I started building yet another web-based app, in Go. Being mostly a back-end developer, I don’t have to write web apps very often, and every time I do, it seems like a great challenge. I often wish someone would write a guide to web development for people who do not have all day to get into the intricacies of great design and just need to build a functional site that works without too much fuss.

I’ve decided to use this opportunity to start from scratch and build it to the best of my understanding of how an app ought to be built in 2017. I’ve spent many hours getting to the bottom of all things I’ve typically avoided in the past, just so that for once in many years I can claim to have a personal take on the matter and have a reusable recipe that at least works for me, and hopefully not just me.

This post is the beginning of what I expect to be a short series highlighting what I’ve learned in the process. The first post is a general introduction describing the present problematic state of affairs and why I think Go is a good choice. The subsequent posts have more details and code. I am curious whether my experience resonates with others, and what I may have gotten wrong, so don’t hesitate to comment!

Edit: If you’d rather just see code, it’s here.

Introduction

In the past my basic knowledge of HTML, CSS and JavaScript has been sufficient for my modest site building needs. Most of the apps I’ve ever built were done using mod_python directly using the publisher handler. Ironically for an early Python adopter, I’ve also done a fair bit of work with Rails. For the past several years I focused on (big) data infrastructure, which isn’t web development at all, though having to build web-based UI’s is not uncommon. In fact the app I’m referring to here is a data app, but it’s not open source and what it does really doesn’t matter for this discussion. Anyway, this should provide some perspective of where I come from when approaching this problem.

Python and Ruby

As recently as a year ago, Python and Ruby would be what I would recommend for a web app environment. There may be other similar languages, but from where I stand, the world is dominated by Python and Ruby.

For the longest time the main job of a web application was constructing web pages by piecing HTML together server-side. Both Python and Ruby are very well suited for the template-driven work of taking data from a database and turning it into a bunch of HTML. There are lots of frameworks/tools to choose from, e.g. Rails, Django, Sinatra, Flask, etc, etc.

And even though these languages have certain significant limitations, such as the GIL, the ease with which they address the complexity of generating HTML is far more valuable than any trade-offs that came with them.

The GIL

The Global Interpreter Lock is worthy of a separate mention. It is the elephant in the room, by far the biggest limitation of any Python or Ruby solution. It is so crippling, people can get emotional talking about it, there are endless GIL discussions in both Ruby and Python communities.

For those not familiar with the problem - the GIL only lets one thing happen at a time. When you create threads and it “looks” like parallel execution, the interpreter is still executing instructions sequentially. This means that a single process can only take advantage of a single CPU.

There do exist alternative implementations, for example JVM-based, but they are not the norm. I’m not exactly clear why, they may not be fully interchangeable, they probably do not support C extensions correctly, and they might still have a GIL, not sure, but as far as I can tell, the C implementation is what everyone uses out there. Re-implementing the interpreter without the GIL would amount to a complete rewrite, and more importantly it may affect the behavior of the language (at least that’s my naive understanding), and so for this reason I think the GIL is here to stay.

Web apps of any significant scale absolutely require the ability to serve requests in parallel, taking advantage of every CPU a machine has. Thus far the only possible solution known is to run multiple instances of the app as separate processes.

This is typically done with help of additional software such as Unicorn/Gunicorn with every process listening on its own port and running behind some kind of a connection balancer such as Nginx and/or Haproxy. Alternatively it can be accomplished via Apache and its modules (such as mod_python or mod_wsgi), either way it’s complicated. Such apps typically rely on the database server as the arbiter for any concurrency-sensitive tasks. To implement caching without keeping many copies of the same thing on the same server a separate memory-based store is required, e.g. Memcached or Redis, usually both. These apps also cannot do any background processing, for that there is a set of tools such as Resque. And then all these components need to be monitored to make sure it’s working. Logs need to be consolidated and there are additional tools for that. Given the inevitable complexity of this set up there is also a requirement for a configuration manager such as Chef or Puppet. And still, these set ups are generally not capable of maintaining a large number of long term connections, a problem known as C10K.

Bottom line is that a simple database-backed web app requires a whole bunch of moving parts before it can serve a “Hello World!” page. And nearly all of it because of the GIL.

Emergence of Single Page Applications

More and more, server-side HTML generation is becoming a thing of the past. The latest (and correct) trend is for UI construction and rendering to happen completely client-side, driven by JavaScript. Apps whose user interface is fully JS-driven are sometimes called Single Page Applications, and are in my opinion the future whether we like it or not. In an SPA scenario the server only serves data, typically as JSON, and no HTML is constructed there. In this set up, the tremendous complexity introduced primarily so that a popular scripting language could be used isn’t worth the trouble. Especially considering that Python or Ruby bring little to the table when all of the output is JSON.

Enter Golang

Go is gradually disrupting the the world of web applications. Go natively supports parallel execution which eliminates the requirement for nearly all the components typically used to work around the GIL limitation.

Go programs are binaries which run natively, so there is no need for anything language-specific to be installed on the server. Gone is the problem of ensuring the correct runtime version the app requires, there is no separate runtime, it’s part of the binary. Go programs can easily and elegantly run tasks in the background, thus no need for tools like Resque. Go programs run as a single process which makes caching trivial and means Memcached or Redis is not necessary either. Go can handle an unlimited number of parallel connections, eliminating the need for a front-end guard like Nginx.

With Go the tall stack of Python, Ruby, Bundler, Virtualenv, Unicorn, WSGI, Resque, Memcached, Redis, etc, etc is reduced to just one binary. The only other component generally still needed is a database (I recommend PostgreSQL). It’s important to note that all of these tools are available as before for optional use, but with Go there is the option of getting by entirely without them.

To boot this Go program will most likely outperform any Python/Ruby app by an order of magnitude, require less memory, and with fewer lines of code.

The short answer is: a framework is entirely optional and not recommended. There are many projects claiming to be great frameworks, but I think it’s best to try to get by without one. This isn’t just my personal opinion, I find that it is generally shared in the Go community.

It helps to think why frameworks existed in the first place. On the Python/Ruby side this was because these languages were not initially designed to serve web pages, and lots of external components were necessary to bring them up to the task. Same can be said for Java, which just like Python and Ruby, is about as old as the web as we know it, or even pre-dates it slightly.

As I remember it, out of the box, early versions of Python did not provide anything to communicate with a database, there was no templating, HTTP support was confusing, networking was non-trivial, bundling crypto would not even be legal then, and there was a whole lot of other things missing. A framework provided all the necessary pieces and set out rules for idiomatic development for all the common web app use cases.

Go, on the other hand, was built by people who already experienced and understood web development. It includes just about everything necessary. An external package or two can be needed to deal with certain specific aspects, e.g. OAuth, but by no means does a couple of packages constitute a “framework”.

If the above take on frameworks not convincing enough, it’s helpful to consider the framework learning curve and the risks. It took me about two years to get comfortable with Rails. Frameworks can become abandoned and obsolete, porting apps to a new framework is hard if not impossible. Given how quickly the information technology sands shift, frameworks are not to be chosen lightly.

I’d like to specifically single out tools and frameworks that attempt to mimic idioms common to the Python, Ruby or the JavaScript environments. Anything that looks or feels or claims to be “Rails for Go”, features techniques like injection, dynamic method publishing and the like which require relying heavily on reflection are not the Go way of doing things, it’s best to stay away from those.

Frameworks definitely do make some things easier, especially in the typical business CRUD world, where apps have many screens with lots of fields, manipulating data in complex and ever-changing database schemas. In such an environment, I’m not sure Go is a good choice in the first place, especially if performance and scaling are not a priority.

Another issue common to frameworks is that they abstract lower level mechanisms from the developer often in way that over time grows to be so arcane that it is literally impossible to figure out what is actually happening. What begins with an idiomatic alias for a single line of JavaScript becomes layers upon layers of transpilers, minimizers on top of helpers hidden somewhere in a sub-dependency. One day something breaks and it’s impossible to know where to even look for the problem. It’s nice to know exactly what is going on sometimes, Go is generally very good about that.

What about the database and ORM?

Similarly to frameworks, Go culture is not big on ORM’s. For starters, Go specifically does not support objects, which is what the O in ORM stands for.

I know that writing SQL by hand instead of relying on User.find(:all).filter... convenience provided to by the likes of ActiveRecord is unheard of in some communities, but I think this attitude needs to change. SQL is an amazing language. Dealing with SQL directly is not that hard, and quite liberating, as well as incredibly powerful. Possibly the most tedious part of it all is copying the data from a database cursor into structures, but here I found the sqlx project very useful.

In Conclusion

I think this sufficiently describes the present situation of the server side. The client side I think could be separate post, so I’ll pause here for now. To sum up, thus far it looks like we’re building an app with roughly the following requirements:

  • Minimal reliance on third party packages.
  • No web framework.
  • PostgreSQL backend.
  • Single Page Application.

part 2

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