RabbitMQ is a very extensible message broker, allowing users to extend the server’s functionality by writing plugins. Many of the broker features are even shipped as plugins that come by default with the broker installation: the Management Plugin, or STOMP support, to name just a couple. While that’s pretty cool, the fact that plugins must be written in Erlang is sometimes a challenge. I decided to see if it was possible to write plugins in another language that targeted the Erlang Virtual Machine (EVM), and in this post I’ll share my progress.
In the last couple of months I’ve been paying attention to a new programming language called Elixir that targets the EVM, and in the last week it became immensely popular inside the Erlang community (and other circles) since Joe Armstrong, the father of Erlang, tried the language, and liked it very much. So I said, OK, lets give it a try.
Here at RabbitMQ HQ we spend quite a lot of time arguing. Occasionally, it's about important things, like what messaging really means, and the range of different APIs that can be used to achieve messaging. RabbitMQ and AMQP present a very explicit interface to messaging: you very much have verbs send and receive and you need to think about what your messaging patterns are. There's a lot (of often quite clever stuff) going on under the bonnet but nevertheless, the interface is quite low-level and explicit, which gives a good degree of flexibility. Sometimes though, that style of API is not the most natural fit for the problem you're trying to solve - do you really reach an impasse and think "What I need here is an AMQP-message broker", or do you, from pre-existing knowledge, realise that you could choose to use an AMQP-message broker to solve your current problem?
retry allows you to abort a transaction but then restart it automatically once someone else has changed one of the variables you read. This means you have the observer-pattern, and from that you can then build any explicit messaging patterns you want. In most cases, I doubt you'll be building APIs that say send or receive, instead you'll be building richer data-structures - work queues, shared dictionaries etc. The question to pose then is: is it easier to build these things based on top of a transaction-like API such as offered by AtomizeJS, or on top of an explicit messaging API such as offered by RabbitMQ and AMQP brokers. There is no one solution and horses-for-courses etc, but please leave your thoughts below.
Recently I saw a tweet saying "ZeroMQ Erlangizes everything!" or some such. While I realise that not everything posted on the web is meant seriously, it does seem there is a stream of similar claims lately that ought to be dammed.
In the article Multi-threading Magic, Pieter Hintjens and Martin Sústrik persuasively explain why concurrency is better served by message-passing than by locks and shared memory. And they are fair, I think, in their analysis -- except for the insinuation that using ZeroMQ transforms your chosen programming language into a domestic Erlang.
Most of us at RabbitMQ HQ have spend time working in a number of functional languages in addition to Erlang, such as Haskell, Scheme, Lisp, OCaml or others. Whilst there is lots to like about Erlang, such as its VM/Emulator, there are inevitably features that we all miss from other languages. In my case, having spent a couple of years working in Haskell before returning to the RabbitMQ fold, all sorts of features are "missing", such as laziness, type classes, additional infix operators, the ability to specify precedence of functions, fewer parenthesis, partial application, more consistent standard libraries and do-notation. That's a fair list, and it'll take me a while to get around to implementing them all in Erlang, but here are two for starters. (more…)