From 61ca86b05493f82bcbddd76911fee64dc636c885 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Lo=C3=AFc=20Hoguin?= Date: Thu, 27 Jun 2013 00:02:12 +0200 Subject: Greatly improve the guide introduction --- guide/erlang_web.md | 181 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 181 insertions(+) create mode 100644 guide/erlang_web.md (limited to 'guide/erlang_web.md') diff --git a/guide/erlang_web.md b/guide/erlang_web.md new file mode 100644 index 0000000..d665ffe --- /dev/null +++ b/guide/erlang_web.md @@ -0,0 +1,181 @@ +Erlang and the Web +================== + +The Web is concurrent +--------------------- + +When you access a website there is little concurrency +involved. A few connections are opened and requests +are sent through these connections. Then the web page +is displayed on your screen. Your browser will only +open up to 4 or 8 connections to the server, depending +on your settings. This isn't much. + +But think about it. You are not the only one accessing +the server at the same time. There can be hundreds, if +not thousands, if not millions of connections to the +same server at the same time. + +Even today a lot of systems used in production haven't +solved the C10K problem (ten thousand concurrent connections). +And the ones who did are trying hard to get to the next +step, C100K, and are pretty far from it. + +Erlang meanwhile has no problem handling millions of +connections. At the time of writing there are application +servers written in Erlang that can handle more than two +million connections on a single server in a real production +application, with spare memory and CPU! + +The Web is concurrent, and Erlang is a language designed +for concurrency, so it is a perfect match. + +Of course, various platforms need to scale beyond a few +million connections. This is where Erlang's built-in +distribution mechanisms come in. If one server isn't +enough, add more! Erlang allows you to use the same code +for talking to local processes or to processes in other +parts of your cluster, which means you can scale very +quickly if the need arises. + +The Web has large userbases, and the Erlang platform was +designed to work in a distributed setting, so it is a +perfect match. + +Or is it? Surely you can find solutions to handle that many +concurrent connections with my favorite language... But all +these solutions will break down in the next few years. Why? +Firstly because servers don't get any more powerful, they +instead get a lot more cores and memory. This is only useful +if your application can use them properly, and Erlang is +light-years away from anything else in that area. Secondly, +today your computer and your phone are online, tomorrow your +watch, goggles, bike, car, fridge and tons of other devices +will also connect to various applications on the Internet. + +Only Erlang is prepared to deal with what's coming. + +The Web is soft real time +------------------------- + +What does soft real time mean, you ask? It means we want the +operations done as quickly as possible, and in the case of +web applications, it means we want the data propagated fast. + +In comparison, hard real time has a similar meaning, but also +has a hard time constraint, for example an operation needs to +be done in under N milliseconds otherwise the system fails +entirely. + +Users aren't that needy yet, they just want to get access +to their content in a reasonable delay, and they want the +actions they make to register at most a few seconds after +they submitted them, otherwise they'll start worrying about +whether it successfully went through. + +The Web is soft real time because taking longer to perform an +operation would be seen as bad quality of service. + +Erlang is a soft real time system. It will always run +processes fairly, a little at a time, switching to another +process after a while and preventing a single process to +steal resources from all others. This means that Erlang +can guarantee stable low latency of operations. + +Erlang provides the guarantees that the soft real time Web +requires. + +The Web is asynchronous +----------------------- + +Long ago, the Web was synchronous because HTTP was synchronous. +You fired a request, and then waited for a response. Not anymore. +It all started when XmlHttpRequest started being used. It allowed +the client to perform asynchronous calls to the server. + +Then Websocket appeared and allowed both the server and the client +to send data to the other endpoint completely asynchronously. The +data is contained within frames and no response is necessary. + +Erlang processes work the same. They send each other data contained +within messages and then continue running without needing a response. +They tend to spend most of their time inactive, waiting for a new +message, and the Erlang VM happily activate them when one is received. + +It is therefore quite easy to imagine Erlang being good at receiving +Websocket frames, which may come in at unpredictable times, pass the +data to the responsible processes which are always ready waiting for +new messages, and perform the operations required by only activating +the required parts of the system. + +The more recent Web technologies, like Websocket of course, but also +SPDY and HTTP/2.0, are all fully asynchronous protocols. The concept +of requests and responses is retained of course, but anything could +be sent in between, by both the client or the browser, and the +responses could also be received in a completely different order. + +Erlang is by nature asynchronous and really good at it thanks to the +great engineering that has been done in the VM over the years. It's +only natural that it's so good at dealing with the asynchronous Web. + +The Web is omnipresent +---------------------- + +The Web has taken a very important part of our lives. We're +connected at all times, when we're on our phone, using our computer, +passing time using a tablet while in the bathroom... And this +isn't going to slow down, every single device at home or on us +will be connected. + +All these devices are always connected. And with the number of +alternatives to give you access to the content you seek, users +tend to not stick around when problems arise. Users today want +their applications to be always available and if it's having +too many issues they just move on. + +Despite this, when developers choose a product to use for building +web applications, their only concern seem to be "Is it fast?", +and they look around for synthetic benchmarks showing which one +is the fastest at sending "Hello world" with only a handful +concurrent connections. Web benchmarks haven't been representative +of reality in a long time, and are drifting further away as +time goes on. + +What developers should really ask themselves is "Can I service +all my users with no interruption?" and they'd find that they have +two choices. They can either hope for the best, or they can use +Erlang. + +Erlang is built for fault tolerance. When writing code in any other +language, you have to check all the return values and act accordingly +to avoid any unforeseen issues. If you're lucky, you won't miss +anything important. When writing Erlang code, you can just check +the success condition and ignore all errors. If an error happen, +the Erlang process crashes and is then restarted by a special +process called a supervisor. + +The Erlang developer thus has no need to fear about unhandled +errors, and can focus on handling only the errors that should +give some feedback to the user and let the system take care of +the rest. This also has the advantage of allowing him to write +a lot less code, and letting him sleep at night. + +Erlang's fault tolerance oriented design is the first piece of +what makes it the best choice for the omnipresent, always available +Web. + +The second piece is Erlang's built-in distribution. Distribution +is a key part of building a fault tolerant system, because it +allows you to handle bigger failures, like a whole server going +down, or even a data center entirely. + +Fault tolerance and distribution are important today, and will be +vital in the future of the Web. Erlang is ready. + +Erlang is the ideal platform for the Web +---------------------------------------- + +Erlang provides all the important features that the Web requires +or will require in the near future. Erlang is a perfect match +for the Web, and it only makes sense to use it to build web +applications. -- cgit v1.2.3