Http Push

“Because as rapid as the arrival of
networked pull media was,
the second act - networked push
media - is coming even faster. ”
WIRED Magazine
March 1997

Thursday, March 11, 2010

Push
A 2010 case study with
the NGINX HTTP Push Module,
Ruby on Rails, and friends

Luke Melia


Who’s this guy?
★ VP, Engineering at weplay.com
★ Agilist
★ nyc.rb’er since ~2006
★ Ruby in Practice contributor
★ Interested in startup tech leadership
★ Beach volleyball player
★ Dad


What’s this talk?
★ The goal and the problem
★ A quick survey of solutions
★ About the NGINX HTTP Push Module
★ How to use it with Ruby, by example
★ Gotchyas
★Q &A


The Goal
★ Immediate encouragement
of positive on-site actions
★ “Points!”


+10


Constraints
★ Don’t want to ﬁgure out points earned
while processing the request (ofﬂoad it to a
background work queue)
★ Do want to inform about points earned
through another user’s actions
★ Don’t want to wait for a second page load


Pure push
doesn’t exist
on the open web


XMPP WebSockets

Push-like
solutions
Streaming Comet

★ Don’t close the connection after
sending down the page
★ multipart/x-mixed-replace
★ Supported in non-Microsoft
browsers only

Streaming

XMPP
★ Designed for presence and messaging
★ Browsers don’t speak XMPP natively
★ BOSH
★ Hemlock: Flex + ejabberd, by NYC’s
Mint Digital


★ Push data over a long held Ajax
request using browser-native
technologies
★ Bayeaux protocol
★ Long-polling Ajax

Comet

WebSockets
★ HTML 5
★ Full-duplex single socket connection
between browser and server
★ ex: ws://websockets.org:8787
★ very limited browser support today


XMPP WebSockets

Streaming Comet

ejabberd Sunshowers

Rainbows!
Servers Cramp

Juggernaut NGINX HTTP Push Module

Orbited
Tornado
Diesel Faye


NGINX HTTP Push Module

★ Turns NGINX into a Comet server
★ “A useful tool with a boring name.”
★ By Leo P
★ http://pushmodule.slact.net/
★ Currently at 0.692β


Basic HTTP Push
Relay Protocol
★ Subscriber locations
★ HTTP GET with channel ID
★ Publisher locations
★ HTTP POST with channel ID
★ POSTed data is passed through,
becoming the response to the
subscriber’s GET


Diagramming the simple case
BACK-END
PROCESS

2. HTTP POST

Publisher endpoint

3. POST BODY
NGINX
IS ROUTED BY
CHANNEL ID
Subscriber endpoint

4. RESPONSE IS
1. HTTP GET DATA FROM
POST BODY

End User


Channel
Concurrency Styles

★ Broadcast

★ Last-in, ﬁrst-out

★ First-in, last-out


Subscriber conﬁg

# public long‐polling endpoint
location /rt/notifications {
  push_subscriber;
  set $push_channel_id $arg_id;
  push_subscriber_concurrency last;
}


Publisher conﬁg
# internal publish endpoint
# (keep it private / protected)
location /rt/publish {
  push_publisher;
  set $push_channel_id $arg_id;
  push_store_messages on;
  push_message_timeout 5m;
  push_max_message_buffer_length 5;
  push_min_message_buffer_length 0;
  push_delete_oldest_received_message on;
}

Diagram with storage
BACK-END
PROCESS

1. HTTP POST

4. MESSAGE Publisher endpoint

2. POST BODY
IS RETRIEVED
IS QUEUED
FROM QUEUE NGINX
Queue
BY CHANNEL ID
BY CHANNEL ID
Subscriber endpoint

5. RESPONSE IS
3. HTTP GET DATA FROM
QUEUE

End User


Code it up.


Client-side Gotchas
★ Javascript blocking
★ Put it in an iframe
★ Per domain connection limit
★ use subdomain, with JSONP


Server-side Gotchas
★ “Too many open connections”
★ Reduce worker_connections to less
than ulimit -n
★ Increase worker_processes to give
you enough total connection to
serve your users
★ Ours: worker_processes 24
worker_connections 960

Testing

★ Fake Publisher for in-memory
cucumber scenarios
★ Run selenium scenarios through
NGINX to incorporate actual
push module behavior


NGINX Conﬁguration
Management

★Template it
★Version
it
★Automate it


The Future
★ Multiplexing: subscribe
to more than one
channel
★ Use Redis as a
message store
★ Convention-based
approach for raising
javascript events


Questions?


Http Push

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