1. ØMQ @ NodeJS
ØMQ: Small Pieces for Scalable Software
Fernando D. Alonso

2. 1. Facts about ØMQ
[ ]

3. Facts about ØMQ
Low level messaging library
○ It is written in C++.
○ A thin layer between application and transport
layers.
○ Message-passing using in-memory queues.
○ Concise API which talks over the ZMTP protocol.
○ Works on top of TCP, IPC, in-memory, and
PGM/EPGM communication protocols.

4. ○ Philosophy: horizontal scalability to reduce points
of failure.
○ Network topology aware. Point to point
communication reduce latencies.
○ Communication is reduced to a few patterns, which
combined are powerful.
○ No need to have a multitenant service.
Facts about ØMQ
A broker is not mandatory

5. Facts about ØMQ
Messaged oriented communication
○ Messages as first-class citizen. No need to fight
with framing or buffering.
○ You can send multipart messages.
○ Messages are atomic.
○ Asynchronous messaging. A single background I/O
thread does the job for ØMQ sockets.
"A ØMQ message is a discrete unit of data passed between
applications or components of the same application. ØMQ messages
have no internal structure and from the point of view of ØMQ itself
they are considered to be opaque binary data."

6. Facts about ØMQ
Fast for development
○ Interchangeable transports: e.g, scaling from one
IPC server to a bunch of TCP.
○ Automatic reconnections.
○ Multicore made easy.
○ Provides zmq_poll to read BSD sockets.

7. ○ It doesn't provide message persistence.
○ It doesn't provide data serialization.
○ It doesn't provide data compression.
○ It doesn't provide message encryption.
○ It doesn't provide security mechanisms. Not in the
next version of the ZMTP protocol !
(*) ZTMP 3.0 draft protocol: http://hintjens.com/blog:39
Facts about ØMQ
Aims for simplicity

8. Facts about ØMQ
Platforms & Languages
○ Bindings for 30+ languages including NodeJS, Ruby,
Python, Java, C, C++, Scala, Erlang, Perl, PHP, .NET.
○ Linux & Windows.
○ Raspberry PI.
○ Android OS.

9. 2. Install
[ , ]

10. Install
On Linux from source
sudo apt-get install build-essential libtool autoconf automake uuid-dev
wget http://download.zeromq.org/zeromq-3.2.3.tar.gz
tar xvzf zeromq-3.2.3.tar.gz
./configure
make
sudo make install
sudo ldconfig
NOTES:
(*) Check http://download.zeromq.org/ for more versions.
(**) Avoid 3.0.x, 3.1.x, 3.2.0, 3.2.1 versions. They lack backwards
compatibility.
(***) Check ./configure --help for more options on build.
(****) ./configure --with-pgm

11. Install
On Linux using packages
Libzmq 3.2:
● Debian Sid: sudo apt-get install libzmq3-dev
Libzmq 2.2:
● Debian Wheezy, Jessie, Sid: sudo apt-get install libzmq-dev
● Debian Squeeze backport: http://packages.debian.org/squeeze-
backports/libzmq1

12. Install
On Mac
brew install zmq

13. Install
NodeJS bindings
NPM Packages:
● zmq (https://github.com/JustinTulloss/zeromq.node) [RECOMMENDED]
● zmq-stream (https://github.com/Schoonology/zmq-stream)
npm install zmq
node
> var zmq = require('zmq');

14. Install
Bindings in other languages
Ruby: https://github.com/chuckremes/ffi-rzmq [RECOMMENDED]
Python: https://github.com/zeromq/pyzmq
Erlang: https://github.com/zeromq/erlzmq2
Java JZMQ (uses JNI): https://github.com/zeromq/jzmq
Java JeroMQ: https://github.com/zeromq/jeromq
Scala ZeroMQ: https://github.com/mDialog/scala-zeromq
Scala ZeroMQ (official): https://github.com/valotrading/zeromq-scala-binding
...

15. 3. Sockets

16. Sockets
Creation
(*) http://api.zeromq.org/3-2:zmq-socket
ØMQ C API
NodeJS ZMQ
req ZMQ_REQ
rep ZMQ_REP
dealer ZMQ_DEALER
router ZMQ_ROUTER
push ZMQ_PUSH
pull ZMQ_PULL
ØMQ C APINodeJS ZMQ
pub ZMQ_PUB
sub ZMQ_SUB
xsub ZMQ_XSUB
xpub ZMQ_XPUB
var sock = zmq.socket
("<SOCKET_TYPE>");
zmq_socket(context, <SOCKET_TYPE>);
Request
Reply
Dealer (async Request)
Router (async Reply)
Push
Pull
Publisher
Subscriber
XSubscriber
XPublisher

17. Sockets
Bind & Connect
sock.bind("tcp://10.0.0.1:5555",
function(err) {
..
});
sock.connect("tcp://10.0.0.1:5555");
sock.close();
(*) http://api.zeromq.org/3-2:zmq-bind
(**) http://api.zeromq.org/3-2:zmq-connect
(***) http://api.zeromq.org/3-2:zmq-close
ØMQ C API
zmq_bind(socket, "tcp://10.0.0.1:5555");
zmq_connect(socket, "tcp://10.0.0.1:
5555");
zmq_close(socket);
NodeJS ZMQ
Bind
Connect
Close

18. Sockets
Bind & Connect
sock.bindSync("tcp://10.0.0.1:5555");
// This line gets executed once the socket
// is binded, but it breaks on error.
NodeJS ZMQ
BindSync

19. Sockets
Transports
TCP
● usage: tcp://<address>:<port>
sock.bind("tcp://192.168.1.100:5555");
sock.bind("tcp://eth0:5555");
// binds to the first eth0 interface
sock.bind("tcp://*:5555");
// binds to all interfaces
(*) http://api.zeromq.org/3-2:zmq-tcp
ØMQ C API
zmq_bind(socket, "tcp://192.168.1.100:
5555");
zmq_bind(socket, "tcp://eth0:5555");
zmq_bind(socket, "tcp://*:5555");
NodeJS ZMQ

20. Sockets
Transports
Inter-Process Communication (IPC)
● usage: ipc://<address>
● Requires RW permissions on the specified path.
(*) http://api.zeromq.org/3-2:zmq-ipc
sock.bind("ipc:///tmp/mysocket");
ØMQ C API
zmq_bind(socket, "ipc:///tmp/mysocket");
NodeJS ZMQ

21. Sockets
Transports
In-process Communication (in-memory)
● usage: inproc://<address>
● Requires to bind before connect.
● Max. address name length is 256.
(*) http://api.zeromq.org/3-2:zmq-inproc
(**) Buggy on node-zmq package.
sock.bind("inproc://queue");
ØMQ C API
zmq_bind(socket, "ipc://queue");
NodeJS ZMQ

22. Sockets
Transports
PGM (multicast)
● usage: pgm://<address>;<multicast_address>:<port>
● Requires sudo privileges to access raw IP sockets.
● Needs ØMQ built with PGM extension (./configure --with-pgm).
(*) http://api.zeromq.org/3-2:zmq-pgm
sock.bind(
"pgm://192.168.1.100;239.192.1.1:3055"
);
ØMQ C API
zmq_bind(socket, "pgm://192.168.1.100;
239.192.1.1:3055");
NodeJS ZMQ

23. Sockets
Transports
Encapsulated PGM (multicast)
● usage: epgm://<address>;<multicast_address>:<port>
● Needs ØMQ built with PGM extension (./configure --with-pgm).
(*) http://api.zeromq.org/3-2:zmq-pgm
sock.bind(
"epgm://192.168.1.100;239.192.1.1:3055"
);
ØMQ C API
zmq_bind(socket, "epgm://192.168.1.100;
239.192.1.1:3055");
NodeJS ZMQ

24. Sockets
Send & Receive
Send
sock.send("My message");
sock.on("message", function(msg) {
console.log(msg.toString());
});
(*) http://api.zeromq.org/3-2:zmq-send
(**) http://api.zeromq.org/3-2:zmq-recv
Receive
sock.on("message", function(msg) {
console.log("Received " + msg);
});
// <msg> is a Buffer object.

25. Sockets
Multipart messages
ØMQ Queue
zmq_send(socket, "Como", 4, ZMQ_SNDMORE);
Messages are atomic
A ØMQ message is composed of 1 or more
message parts.
zmq_send(socket, "andas", 5, 0);
4 ComoPart 1
5 andasPart 2
ØMQ ensures that peers receive either all message parts of a message or
none at all.
The total number of message parts is unlimited except by available memory.

26. Sockets
Multipart messages
sock.send("First part", zmq.ZMQ_SNDMORE);
sock.send("Second part");
sock.send(["First part", "Second part"]);
Send
var r = sock.send("Como", zmq.
ZMQ_SNDMORE);
console.log(r);
Check the outgoing buffer and socket state:
running this
will output ->
> { type: 'req',
_zmq: { state: 0, onReady:
[Function] },
_outgoing: [ [ <Buffer 43 6f
6d 6f>, 2 ] ],
_shouldFlush: true,
_events: { message: [Function]
} }

27. Sockets
Multipart messages
sock.on("message", function(first_part, second_part) {
console.log(first_part.toString());
console.log(second_part.toString());
});
sock.on("message", function() {
for(var key in arguments) {
console.log("Part " + key + ": " + arguments[key]);
};
});
Receive
sock.on("message", function() {
var messages = Array.prototype.slice.call(arguments);
messages.forEach(function(msg) {
console.log("Part:" + msg);
});
});

28. Sockets
Batched messaging
ØMQ Queue
3 Msg
"ØMQ batches messages in opportunistic manner. It sends all the
messages available at the moment in one go. Latency of subsequent
messages will be improved because sending single batch to the card
is faster then sending lot of small messages."
sock.send("Part A",
zmq.ZMQ_SNDMORE);
sock.send("Msg");
sock.send("Part
B");
6 Part A
6 Part B
ØMQ Socket
send
send
send
<write busy>
<write ready>
Client Thread ØMQ I/O Thread
send
batch
<write busy>

29. Patterns
Plugging multiple transports
Example
var zmq = require('zmq'),
pub = zmq.socket('pub');
pub.bindSync('tcp://127.0.0.1:5555');
pub.bindSync('ipc:///tmp/zmq.sock');
setInterval(function() {
pub.send("I am polyglot!");
}, 1000);
sub = zmq.socket('sub');
sub.connect('ipc:///tmp/zmq.sock');
sub.subscribe('');
sub.on('message', function(msg) {
console.log("Received: " + msg);
});
var zmq = require('zmq'),
sub = zmq.socket(sub');
sub.connect('tcp://127.0.0.1:5555');
sub.subscribe('');
sub.on('message', function(msg) {
console.log(Received: ' + msg);
});

30. Sockets
Setting Socket Options
(*) http://api.zeromq.org/3-2:zmq-setsockopt
Setsockopt
● usage (NodeJS ZMQ API): sock.setsockopt(<option>, <value>);
or sock.<option> = <value>;
sock.identity = 'monitor-1';
sock.setsockopt('identity', 'monitor-1');
Identity:
// value can be any string up to 255 length.
// identity is required on sockets
// connecting to a Router.

31. Sockets
Setting Socket Options
Setsockopt
subscriber.subscribe('MUSIC');
subscriber.setsockopt('subscribe',
'MUSIC');
Subscribe:
// sets a message filter for subscriber sockets.
subscriber.unsubscribe('MUSIC');
susbscriber.setsockopt('subscribe',
'POP');
Unsubscribe:
// sets off a message filter for subscriber
sockets.

32. 4. Patterns
[ ]

33. Patterns
Request / Reply
Synchronous task distribution
Ø REP #1
Ø REP # 2
Ø REQ
< round robin >
...
< synchronous >
Used when each message needs to be matched with a response. Handles
only one message at time. Strict send-recv cycle.

34. Patterns
Request / Reply
Ø REP #1 Ø REP # 2Ø REQ
send
recv (wait response)
send
recv (dont wait response)
recv (dont wait response)

35. Patterns
Request / Reply
Ø REP #1 Ø REP # 2Ø REQ
send
recv
recv
send
send
-> REP #1 is down
FAILURE
REQ #1 will not recover !

36. Patterns
Request / Reply
Basic Request / Reply
var zmq = require('zmq');
reply = zmq.socket('rep');
reply.bind('tcp://127.0.0.1:5555',
function(err) {
if (err) throw err;
}
);
reply.on('message', function(msg) {
console.log('Received: ' + msg);
reply.send('Pong!');
});
var zmq = require('zmq');
request = zmq.socket('req');
request.connect('tcp://127.0.0.1:5555');
request.send('Ping');
request.on('message', function(msg) {
console.log('Response: ' + msg);
});

37. Patterns
Request / Reply
Dealer socket message delivery
Messages have to be multipart, consisting on: an empty delimiter header,
followed by the content body parts.
sock.send("Body");
Outgoing Queue
0
6 Body
sock.send(new Buffer([]), zmq.
ZMQ_SNDMORE);
send
send

38. Patterns
Request / Reply
Dealer socket message delivery
Outgoing messages are round-robined among all connected peers.
However, sending depends on the availability of the receiver.
sock.send(
["", "Msg"]);
Outgoing Queue
3 Msg
6 Part A
Peer Socket A Peer Socket B
sock.send(
["", "Bla");
sock.send(
["", "Msg2"]);
send
send
send
To A
To B
To A
send
<write
ready>
<write
busy>
<write
ready>
0
0
4 Msg2
0

39. Patterns
Request / Reply
Dealer socket message delivery
Reconnections are handled automatically: messages are asynchronously
delivered. Response time does not block sending more messages.
Outgoing Queue Peer Socket A Peer Socket B
send
-> Up again
sock.send(
["", "Msg"]);
3 Msg
sock.send(
["", "Msg2"]);
send
send
To A
To A
0
4 Msg2
0

40. Patterns
Request / Reply
Ø REP #1 Ø REP # 2Ø DEALER
enqueue < Msg A >
send < Msg B >
-> REP #1 is down
enqueue < Msg C >
send < Msg A, Msg C >
send < Msg D >
Dealer socket handles peer reconnection automatically. It will send
messages that queued for that peer once it has established connection.

41. Patterns
Request / Reply
> Response from: 5001
> Response from: 5001
> Response from: 5002
> Response from: 5001
> Response from: 5001
> Response from: 5002
> ...
Dealer example
var dealer = zmq.socket('dealer');
dealer.connect('tcp://127.0.0.1:5001');
dealer.connect('tcp://127.0.0.1:5002');
setInterval(function() {
dealer.send(["", "Msg"]);
}, 1000);
dealer.on('message', function(h, msg) {
console.log('Response from: ' + msg);
});
running this
'might' output
->

42. Patterns
Request / Reply
Router socket messaging
Messages have to be multipart, consisting on: an identity frame, an empty
delimiter frame, followed by the content body parts. This applies to both
incoming and outgoing messages.
sock.send("Body");
Outgoing Queue
0
6 Body
sock.send("", zmq.
ZMQ_SNDMORE);
send
send
sock.send(
"worker-1", zmq.
ZMQ_SNDMORE); 8 worker-1
send

43. Patterns
Request / Reply
Router is asynchronous
Incoming messages are fair-queued among all connected and available
peers.
Peer Socket A Peer Socket B
ØMQ Router
Incoming Queue
Socketsend
send
send

44. Patterns
Request / Reply
Router is asynchronous
Receiving depends on the availability of the sender.
Peer Socket A Peer Socket B
ØMQ Router
Incoming Queue
Socketsend
send

45. Patterns
Push / Pull
Unidirectional data distribution
The Push / Pull pattern fits well on pipelined communication, i.e., when no
response is required for a given message.
Ø
Ø
...
ØØ

46. Patterns
Push / Pull
Binding the Push socket
Outgoing messages are round-robined among all connected and available
peers.
push.send("Msg");
push.send("Part
B");
Outgoing Queue Peer Socket A Peer Socket B
push.send("Part A",
zmq.ZMQ_SNDMORE);
push.send("Msg2");
3 Msg
6 Part A
6 Part B
4 Msg2
send
send
send
send

47. Patterns
Push / Pull
Binding the Push socket
Outgoing messages are round-robined among all connected and available
peers.
Outgoing Queue Peer Socket A Peer Socket B
-> Down3 Msg
6 Part A
6 Part B
4 Msg2
send
send
send
push.send("Msg");
push.send("Part
B");
push.send("Part A",
zmq.ZMQ_SNDMORE);
push.send("Msg2");
send
send
send
send

48. Patterns
Push / Pull
Binding the Push socket
Disconnections and reconnections are handled automatically.
Outgoing Queue Peer Socket A Peer Socket B
4 More
6 Part 1
6 Part 2
5 Other
send
send
send
push.send("More"); send
push.send("Part
2");
push.send("Part 1",
zmq.ZMQ_SNDMORE);
send
send
push.send("Other");
send

49. Patterns
Push / Pull
Parallel task distribution
Ø PULL #1
Ø PULL # 2
Ø PUSH
< round robin >
...

50. Patterns
Push / Pull
Passive agents / Monitor
Ø PULLØ PUSH
...
Ø PUSH

51. Patterns
Push / Pull
Binding the Pull socket
Push's outgoing messages are round-robined among all connected peers.
push.send("Msg");
push.send("Part
B");
Outgoing Queue Peer Socket A Peer Socket B
push.send("Part A",
zmq.ZMQ_SNDMORE);
push.send("Msg2");
send
send
send
send
3 Msg
6 Part A
6 Part B
4 Msg2
To A
To B
To A

52. Patterns
Push / Pull
Binding the Pull socket
Push's outgoing messages are round-robined among all connected peers.
push.send("Msg");
push.send("Part
B");
Outgoing Queue Peer Socket A Peer Socket B
push.send("Part A",
zmq.ZMQ_SNDMORE);
push.send("Msg2");
send
send
send
send
send
send
send
3 Msg
6 Part A
6 Part B
4 Msg2
To A
To B
To A

53. Patterns
Push / Pull
Binding the Pull socket
Disconnections and reconnections are handled automatically.
Outgoing Queue Peer Socket A Peer Socket B
send
send
-> Down4 More
6 Part 1
6 Part 2
5 Other
To A
To A
To B
push.send("More"); send
push.send("Part
2");
push.send("Part 1",
zmq.ZMQ_SNDMORE);
send
send
push.send("Other");
send

54. Patterns
Push / Pull
Binding the Pull socket
Sending is asynchronous, it depends on the availability of the receiver.
Outgoing Queue Peer Socket A Peer Socket B
send
-> Up again
5 OtherTo B
push.send("More"); send
push.send("Part
2");
push.send("Part 1",
zmq.ZMQ_SNDMORE);
send
send
push.send("Other");
send

55. Patterns
Push / Pull
Ø PULLØ PUSH #1
...
Ø PUSH #2
Active agents / collector pattern

56. Patterns
Publish / Subscribe
Broadcast data distribution
Ø SUB #1
Ø PUB #1
...
Ø SUB #2
Ø SUB #2

57. Message distribution
Patterns
Publish / Subscribe
sock.send("Msg");
Outgoing Queue
3 Msg
Subscriber A
Subscriber B
send
send
Outgoing messages are send to each connected and available peers.
Subscriber C

58. Message distribution
Patterns
Publish / Subscribe
sock.send("Msg");
Outgoing Queue
3 Msg
Subscriber A
Subscriber B
send
send
Outgoing messages are send to each connected and available peers.
Subscriber C
5 Othersock.send("Other");
send

59. Subscribers can register to a specific topic.
Data filtering
Patterns
Publish / Subscribe
ØMQ Publisher
Subscriber A
Subscriber B
Subscriber C
Outgoing Queue
subscribe AR
subscribe VE
Socket
subscribe VE

60. Subscribers can register to a specific topic.
Data filtering
Patterns
Publish / Subscribe
ØMQ Publisher
Subscriber A
Subscriber B
Subscriber C
Outgoing Queue
subscribe AR
subscribe VE
Socket
subscribe VE
sock.send("AR
news");
send
7 AR news
send

61. Subscribers can register to a specific topic.
Data filtering
Patterns
Publish / Subscribe
ØMQ Publisher
Subscriber A
Subscriber B
Subscriber C
Outgoing Queue
subscribe AR
subscribe VE
Socket
subscribe VE
sock.send("VE
news");
send
7 VE news
sendsend

62. Patterns
Publish / Subscribe
Data filtering example
pub = zmq.socket('pub');
pub.bindSync("tcp://10.0.0.12:3055");
count = 0
setInterval(function() {
pub.send("TEST " + count++);
}, 1000);
sub = zmq.socket('sub');
sub.connect("tcp://10.0.0.12:3055");
sub.subscribe("TEST");
sub.on("message", function(msg) {
console.log("Received: " + msg);
});
// older messages won't be
// received
> TEST 6
> TEST 7
> TEST 8
> TEST 9
> TEST 10
running this
'might'
output ->

63. Patterns
Publish / Subscribe
Multicast example
var zmq = require('zmq'),
pub = zmq.socket('pub');
pub.bind(
"epgm://10.0.0.12;239.192.1.1:3055",
function(err) {
if(err) throw err;
}
)
setInterval(function() {
pub.send("From pid: " + process.pid);
}, 1000);
var zmq = require('zmq'),
sub = zmq.socket('sub');
sub.connect(
"epgm://10.0.0.13;239.192.1.1:3055"
);
sub.subscribe("");
sub.on('message', function(msg) {
console.log("Received " + msg);
});
(*) See running demo at http://youtu.be/NQrH0SATPk0

64. "XSUB and XPUB are exactly like SUB and PUB except they expose
subscriptions as special messages."
Data distribution proxy
Patterns
XSUB / XPUB
XSUB/XPUB Proxy
Subscriber A
Subscriber B
Subscriber C
XPUB Socket
XSUB Socket
Publisher A
Publisher B
Publisher C
subscribe
PY
forward
subscription

65. Messages are forwarded by the proxy to the registered subscribers.
Data distribution proxy
Patterns
XSUB / XPUB
XSUB/XPUB Proxy
Subscriber A
Subscriber B
Subscriber C
XPUB Socket
XSUB Socket
Publisher A
Publisher B
Publisher C
forward
message
send "PY<msg>"
send

66. 5. Useful links
[ ]

67. Useful Links
Workshop examples
http://github.com/krakatoa/node_zmq_workshop

68. Useful Links
The Guide
http://zguide.zeromq.org/page:all

69. Useful Links
Pieter Hintjens personal blog
http://hintjens.com/

70. Useful Links
API References
http://api.zeromq.org/3-2:zmq-socket
http://api.zeromq.org/3-2:zmq-setsockopt

71. Preguntas ?
fedario@gmail.com
github.com/krakatoa
Fernando Dario Alonso
Gracias !