I wish to create a platform as a service in the financial markets using Erlang/Elixir. I will provide AWS lambda-style functions in financial markets, but rather than being accessible via web/rest/http, I plan to distribute my own ARM-based hardware terminals to clients (Nvidia Jetson TX2-based or similar, so decent hardware). They will access the functions from these terminals. I want said terminals to be full nodes in the system. So they will use the actor model to message pass to my central servers, and indeed, the terminals might message pass amongst each other if terminal users decide to put their own functions online.
Is this a viable model? Could I run 1000 terminals like this? 100 000? What kinds of limitations might I start bumping into? Is Erlang message routing scalable enough to imagine such a network still being performant if we had soft-real time financial markets streaming data flowing around? (mostly from central servers to terminals, but a good proportion possible moving directly around from terminal to terminal). We could have a system where up to 100k or more different "subscription" data channel processes were available, many of them taking input and producing output every second.
Basically I'd like a canonical guide to the scalability capabilities of an Erlang system something like the above. Ideally I'd also like some guide to the security implications of such a system ie. would global routing tables or any other part of the system be compromisable by a rogue terminal user, or can edge nodes be partly "sealed off" from sensitive parts of the rest of the Erlang network?
Note that I'd want to make heavy use of ports/NIFs for high-compute processes.
I would not pursue this avenue for various reasons, all of which hark back to the sort of systems that Erlang's distribution mechanism was developed for - a set of boards on a passive backplane: "free" local bandwidth and the whole machine sits in the same security domain. The Erlang distribution protocol is probably too chatty to work well on widely spread and large networks, and it is certainly too insecure. Unless you want nodes to be able to execute :os.cmd("rm -rf /") on each other, of course.
Use the Erlang distribution protocol in your central system to your heart's content, and have these terminals talk something that's data-only-over-SSL to that system and each other. On top of that, you can quite simply build a sort of overlay network to do whatever you want.
I recommend read this carefully and i recommend divide your service to little Micro-Services too.
Another benchmark is Investigating the Scalability Limits of
Distributed Erlang.
In the Joe Armstorng's book programming Erlang, he said:
"A few years ago, when I had my research hat on, I was working with PlanetLab. I had access to the PlanetLab a network, so I installed empty Erlang servers on all the PlanetLab machines (about 450 of them).
I didn’t really know what I would do with the machines, so I just set up the server infrastructure to do something later."
Do not use External ports, use internal drivers which are written in C or C++ instead.
You will find a lot of information regarding erlang Architectures is this answer: How scalable is distributed Erlang?
Short answer is, there is a pratical limitation of nodes in a cluster, but this limitation can be breach with federations fairly easily.
EDIT 1/ Further more I would recommend to read this book : Designing for scalability with Erlang/OTP
do you have any experience with SD Erlang project?
There seems to be implemented many interesting concepts regarding the comm mesh optimalizations and I'm just curious if some of you used those in production already or in some real project at least.
SD erlang repo
Thanks!
The project has finished a week ago. The main ideas behind SD Erlang are reducing the number of connections Erlang nodes maintain while keeping transitivity and common namespace for groups of nodes. Benchmarks that we used (Orbit, Ant Colony Optimization (ACO), and Instant Messenger) showed very promising results. Unfortunately, we didn't have enough human resources to refactor Sim-Diasca simulation engine. So, no, SD Erlang hasn't been used yet in a real application.
At the moment we are writing up the last deliverable that will provide an overview of what has been achieved. It will appear here in a few weeks (D6.2). In general we are happy with the results we get using SD Erlang, so there are plans for a follow up project to continue to work on it but currently this is work in progress.
This is not a direct answer but I will use SD-Erlang in a embedded application which needs to scale to hundreds of nodes (small embedded CPUs). From what I have seen its ready to be tried out in a real application. To furtehr evaluate lets consider the alternatives:
You have only a few distributed nodes: then you probably don't need it and can just connect all the nodes and for name registry use either the global module (slow but sturdy) or gprocwith the new locks_leader branch which avoids the quite broken gen_leader which so far prevented using gproc in distributed mode in production.
You need many nodes (how many depends on your hardware and requirements but you start to get into interesting territory with > 70 nodes)
Use SD-Erlang and fix whatever problems you encounter in production, or at least report them. It certainly solves a lot of the problems you get with normal Erlang distribution
Roll your own solution either with playing with different cookie values or with hidden nodes: hint you can set different cookie values for different peer nodes. But then you need to roll your own global name registry and management code: looks like a variant of Greenspuns 10th rule or closer to Erlang Virdings 1st rule : you probably will result in implementing half of SD Erlang yourself.
Don't use Erlang distribution at all. That seems to be the industry standard that for anything involving more nodes or crossing data-centers you shouldn't use Erlang distribution at all but run your own protocols. My personal opinion is to rather fix Erlang Distributions problems than just ditch it. Its much too useful and time saving when it works for a use case to just give up on it. And I see SD-Erlang as being the fix for the "too many nodes" problem, its at least the right starting point.
I am trying to ilustrate the concept of distributed applications using Erlang. My system currently has one server and one ATM. I try to keep it as simple as possible.
For the moment my application runs locally. I am using gen_server for a client-server relationship between the banking server and the ATM. I also have a gen_fsm module to suggest different states my ATM has. In order to store any data i use the dict module (I don't want to make things more complicated using databases). To keep processes alive (the gen_server and gen_fsm) I am using a supervisor process. I've wrapped all modules as an application but for the moment it's all local. Any ideas would be highly appreciated.
I was thinking to start the same application on two different nodes and to illustrate the distributed concept to use some kind of failover/takeover mechanism but I have no ideas on what modules to use.
Is it mandatory to use target systems?(at some point i must do a hot upgrade to the application)
What's the correct order to do these things: first to upgrade and then distribute?
I would be very grateful if someone could give me some ideas on how to accomplish all those things.
I never tried it myself, but docs seem to point to:
Erlang Release Handling (11.3 Distributed Systems).
It's a really short paragraph showing the sync_nodes command, I suggest you to read the whole chapter because I noticed that often the concepts of concurrency and distribution are so persavive in Erlang that problems like yours have already been solved and included in OTP.
BTW, Erlang user guide also has a whole chapter dedicated to Distributed Applications that seems related to distributed applications config options, I think that the two should do the trick.
Hope this helps, if you need more help just ask!
I think Erlang is very well suited for server systems developed in my workplace (currently developed in Java). I am a bit skeptical how this would be accepted both by developers (who have no idea about functional or Erlang) and by managers.
Any ideas on how to approach the issue? I am thinking about some hybrid system, where the hardcore highly reliable infra uses Elrang, and app specific stuff developed in Java (as nodes?)
There are a few approaches, and neither have any guarantees to actually work
Implement something substantial in a short time frame, perhaps using your own time. Don't tell anyone until you have something to display that works. Unless you have a colleague in on it.
Pull up lots of Erlang projects that are good demonstrations of the features you want. Present it to your managers and try to frame them about the risk in keeping using Java with this kind of technology available.
If the company you work for actually have a working code base in Java already, they're not likely to take you seriously when you suggest to rewrite it in another language.
The true test that you believe in Erlang being a much better choice: Quit and start up a competing company and bring the technology insight you have in your current industry. Your managers are really comparing a similar risk-scenario as you would do if you were to quit your job, and they are looking for the same assuring facts for success as you would do, to consider leaving a "safe" paycheck.
As for how to integrate, check out the jinterface application in Erlang. It allows Java code to send messages to Erlang nodes, and it allows Java to expose mailboxes to the Erlang nodes as if there were Erlang processes.
It's all about ROI (Return On Investment) to a manager: a manager will be concerned about performance (of the company). In order to appeal to his business nature, you'll have to make a case for it using dollar$ (or whatever appropriate currency).
Beware that undertaking a "skunkwork" project on the side to "prove" your solution based on Erlang might backfire: "so you had time to play with Erlang, why didn't you spend the time on the project then?" (Of course, not all managers/companies would think this way).
You have to take into account the whole proposal e.g. impact on the team, skills to be developed etc. It's all about money.
If I have an advice for you: start small, plant a seed, nurture it and watch it grow.
A wise man once said to me:
"It's not about technology, it's about
the product & market".
Start by not targetting a rewrite but using erlang for a new feature/project. Rewrites can be expensive and taking a chance on erlang for something that is already a time consuming and costly undertaking is a hard sell. But if there is a new piece that could be done in erlang and java, you stand a better chance. The project will be small enough hopefully that you can discover early if erlang is a good fit and adapt accordingly. And when erlang proves itself in that project you will have better data to make your case with.
We're introducing RabbitMQ into our infrastructure, which currently runs a combination of C++, Java and Python applications. I'm not specifically intending to move the team towards Erlang, but if I were, introducing a well-written third-party tool that just happens to use Erlang is a very good way to get the foot in the door.
One major caveat is that while Erlang is a wonderful language to learn, the surrounding technology (OTP in particular) has a huge learning curve and is extremely primitive in many ways (debugging, IDE's, etc.). It is getting better all the time, but reluctant converts will crucify you if you don't warn them about the pain of learning to program in a radically different environment. Even simple things like the lack of code-sense technology (E.g., type 'foo.' and the IDE tells you what methods you can call on foo) can leave a really bad taste in the mouth.
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I would like to know a list of the most common application/websites/solutions where Erlang is used, successfully or not.
Explaining why it is used into a specific solution instead of others programming languages would be very much appreciated, too.
Listing BAD Erlang case studies (cases in which Erlang is misused) it would be interesting, as well.
From Programming Erlang:
(source: google.com)
Many companies are using Erlang in their production systems:
• Amazon uses Erlang to implement SimpleDB, providing database services as a part
of the Amazon Elastic Compute Cloud (EC2).
• Yahoo! uses it in its social bookmarking service, Delicious, which has more than
5 million users and 150 million bookmarked URLs.
• Facebook uses Erlang to power the backend of its chat service, handling more than
100 million active users.
• WhatsApp uses Erlang to run messaging servers, achieving up to 2 million connected users per server.
• T-Mobile uses Erlang in its SMS and authentication systems.
• Motorola is using Erlang in call processing products in the public-safety industry.
• Ericsson uses Erlang in its support nodes, used in GPRS and 3G mobile networks
worldwide.
The most popular open source Erlang applications include the following:
• The 3D subdivision modeler Wings 3D, used to model and texture polygon
meshes.
• The Ejabberd system, which provides an Extensible Messaging and Presence Protocol
(XMPP) based instant messaging (IM) application server.
• The CouchDB “schema-less” document-oriented database, providing scalability
across multicore and multiserver clusters.
• The MochiWeb library that provides support for building lightweight HTTP servers.
It is used to power services such as MochiBot and MochiAds, which serve
dynamically generated content to millions of viewers daily.
• RabbitMQ, an AMQP messaging protocol implementation. AMQP is an emerging
standard for high-performance enterprise messaging.
ejabberd is one of the most well know erlang application and the one I learnt erlang with.
I think it's the one of most interesting project for learning erlang because it is really building on erlang's strength. (However some will argue that it's not OTP, but don't worry there's still a trove of great code inside...)
Why ?
An XMPP server (like ejabberd) can be seen as a high level router, routing messages between end users. Of course there are other features, but this is the most important aspect of an instant messaging server. It has to route many messages simultaneously, and handle many a lot of TCP/IP connections.
So we have 2 features:
handle many connections
route messages given some aspects of the message
These are examples where erlang shines.
handle many connections
It is very easy to build scalable non-blocking TCP/IP servers with erlang. In fact, it was designed to solve this problem.
And given it can spawn hundreds of thousand of processes (and not threads, it's a share-nothing approach, which is simpler to design), ejabberd is designed as a set of erlang processes (which can be distributed over several servers) :
client connection process
router process
chatroom process
server to server processes
All of them exchanging messages.
route messages given some aspects of the message
Another very lovable feature of erlang is pattern matching.
It is used throughout the language.
For instance, in the following :
access(moderator, _Config)-> rw;
access(participant, _Config)-> rw;
access(visitor, #config{type="public"})-> r;
access(visitor, #config{type="public_rw"})-> rw;
access(_User,_Config)-> none.
That's 5 different versions of the access function.
Erlang will select the most appropriate version given the arguments received. (Config is a structure of type #config which has a type attribute).
That means it is very easy and much clearer than chaining if/else or switch/case to make business rules.
To wrap up
Writing scalable servers, that's the whole point of erlang. Everything is designed it making this easy. On the two previous features, I'd add :
hot code upgrade
mnesia, distributed relational database (included in the base distribution)
mochiweb, on which most http erlang servers are built on
binary support (decoding and encoding binary protocol easy as ever)
a great community with great open source projects (ejabberd, couchdb but also webmachine, riak and a slew of library very easy to embed)
Fewer LOCs
There is also this article from Richard Jones. He rewrote an application from C++ to erlang: 75% fewer lines in erlang.
The list of most common applications for Erlang as been covered (CouchDb, ejabberd, RabbitMQ etc) but I would like to contribute the following.
The reason why it is used in these applications comes from the core strength of Erlang: managing application availability.
Erlang was built from ground up for the telco environment requiring that systems meet at least 5x9's availability (99.999% yearly up-time). This figure doesn't leave much room for downtime during a year! For this reason primarily, Erlang comes loaded with the following features (non-exhaustive):
Horizontal scalability (ability to distribute jobs across machine boundaries easily through seamless intra & inter machine communications). The built-in database (Mnesia) is also distributed by nature.
Vertical scalability (ability to distribute jobs across processing resources on the same machine): SMP is handled natively.
Code Hot-Swapping: the ability to update/upgrade code live during operations
Asynchronous: the real world is async so Erlang was built to account for this basic nature. One feature that contributes to this requirement: Erlang's "free" processes (>32000 can run concurrently).
Supervision: many different strategies for process supervision with restart strategies, thresholds etc. Helps recover from corner-cases/overloading more easily whilst still maintaining traces of the problems for later trouble-shooting, post-mortem analysis etc.
Resource Management: scheduling strategies, resource monitoring etc. Note that the default process scheduler operates with O(1) scaling.
Live debugging: the ability to "log" into live nodes at will helps trouble-shooting activities. Debugging can be undertaken live with full access to any process' running state. Also the built-in error reporting tools are very useful (but sometimes somewhat awkward to use).
Of course I could talk about its functional roots but this aspect is somewhat orthogonal to the main goal (high availability). The main component of the functional nature which contributes generously to the target goal is, IMO: "share nothing". This characteristic helps contain "side effects" and reduce the need for costly synchronization mechanisms.
I guess all these characteristics help extending a case for using Erlang in business critical applications.
One thing Erlang isn't really good at: processing big blocks of data.
We built a betting exchange (aka prediction market) using Erlang. We chose Erlang over some of the more traditional financial languages (C++, Java etc) because of the built-in concurrency. Markets function very similarly to telephony exchanges. Our CTO gave a talk on our use of Erlang at CTO talk.
We also use CouchDB and RabbitMQ as part of our stack.
Erlang comes from Ericsson, and is used within some of their telecoms systems.
Outside telecoms, CouchDb (a document-oriented database) is possibly the best known Erlang application so far.
Why Erlang ? From the overview (worth reading in full):
The document, view, security and
replication models, the special
purpose query language, the efficient
and robust disk layout and the
concurrent and reliable nature of the
Erlang platform are all carefully
integrated for a reliable and
efficient system.
I came across this is in the process of writing up a report: Erlang in Acoustic Ray Tracing.
It's an experience report on a research group's attempt to use Erlang for Acoustic Ray Tracing. They found that while it was easier to write the program, less buggy, etc. It scaled worse, and performed 10x slower than a comparable C program. So one spot where it may not be well suited is CPU intensive scenarios.
Do note though, that the people wrote the paper were in the stages of first learning Erlang, and may not have known the proper development procedures for CPU intensive Erlang.
Apparently, Yahoo used Erlang to make something it calls Harvester. Article about it here: http://www.ddj.com/architect/220600332
What is erlang good for?
http://beebole.com/en/blog/erlang/why-erlang/
http://www.aquabu.com/2008/2/15/erlang-pragmatic-studio-day-3-notes
http://www.reddit.com/r/programming/comments/9q0lr/erlang_and_highfrequency_trading/
(jerf's answer)
It's important to realize that Erlang's 4 parts: the language itself, the VMs(BEAM, hipe) standard libs (plus modules on github, CEAN, etc.) and development environment are being steadily updated / expanded/improved. For example, i remember reading that the floating point performance improved when Wings3d's author realized it needed to improve (I can't find a source for this). And this guy just wrote about it:
http://marian-dan.com/wordpress/?p=324
A couple years ago, Tim Bray's Wide Finder publicity and all the folks starting to do web app frameworks and HTTP servers lead (at least in part) to improved regex and binaries handling. And there's all the work integrating HiPE and SMP, the dialyzer project, multiple unit testing and build libs springing up, ..
So its sweet spot is expanding, The difficult thing is that the official docs can't keep up very well, and the mailing list and erlang blogosphere volume are growing quickly
We are using Erlang to provide the back-end muscle power for our really real-time browser-based multi-player game Pixza. We don't use Flash or any other third-party plugins, though the game is real-time multi-player. We use pure JS and COMET techniques instead. And Erlang supports the "really realtimeliness" of Pixza.
I'm working for wooga, a social game company and we use Erlang for some of our game backends (basically http apis for millions of daily users) and auxiliary services like ios push notification provider, payment etc.
I think it really shines in network related tasks and it makes it kind of straight forward to structure and implement simple and complex network services alike in it. Distribution, fault tolerance and performance are easy to achieve because Erlang already has some of the key ingredients built in and they are being used for a long time in critical production infrastructure. So its not like "the new hip technology thing 0.0.2 alpha".
I know that other game companies use Erlang as well. You should be able to find presentations on slideshare about that.
Erlang draws its strength from being a functional language with no shared memory. Hence IMO, Erlang won't be suitable for applications that require in place memory manipulations. Image editing for example.