Where is Erlang used and why? [closed]

Answer 1

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.

Answer 2

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.

Answer 3

From Programming Erlang:

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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.

Answer 4

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.

Answer 5

Apparently, Yahoo used Erlang to make something it calls Harvester. Article about it here: http://www.ddj.com/architect/220600332

Answer 6

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.