When dynamic becomes static - the next step in web caching techniques

When dynamic becomes static
(the next step in web caching techniques)
Wim Godden
Cu.be Solutions
@wimgtr

Who am I ?
Wim Godden (@wimgtr)
Founder of Cu.be Solutions (http://cu.be)
Open Source developer since 1997
Developer of OpenX, PHPCompatibility, PHPConsistent, ...
Speaker at Open Source conferences

Who are you ?
Developers ?
System/network engineers ?
Managers ?

Quick note
Whenever you see
feel free to think

To understand the present
Understand the past

The Stone Age
New blog post by : caveman003

Pre-dynamic : draw it and make html

Old-school dynamic : 'rebuild-every-time'

Dynamic content in static content

Typical website structure
Header
Latest news
Article content page
Page content
Navigation

Caching blocks with individual TTLs
Top header
(cache for 2h)
Latest news
Page content
Navigation
(cache for 1h)

Caching blocks with individual cache duration
Top header
(cache for 2h)
Latest news (cache for 2m)
Page content (cache for 30m)
Navigation
(cache for 1h)

ESI – how it works
GET /page GET /page

GET /page GET /page
<html>
...
<esi:include src="/top"/>
<esi:include src="/nav"/>
<div id=”something”>
<esi:include src="/latest-news"/>
</div>
<esi:include src="/article/id/732"/>
...
</html>

GET /top
<div id=”top-part”>
<a href=”/login”>Login</a>
</div>

GET /page GET /page
<html>
...
<div id=”top-part”>
<a href=”/login”>Login</a>
</div>
<esi:include src="/nav"/>
<div id=”something”>
<esi:include src="/latest-news"/>
</div>
<esi:include src="/article/id/732"/>
...
</html>

Varnish - what can/can't be cached ?
Can :
Static pages
Images, js, css
Static parts of pages that don't change often (ESI)
Can't :
POST requests
Very large files (it's not a file server !)
Requests with Set-Cookie
User-specific content

ESI → no caching on user-specific content ?
Logged in as : Wim Godden
5 messages
cache for cache for 5min
1h
cache for 0s ?

Avoid hitting the backend
GET /page
DB

No more backend
GET /page
+ SLIC

Requesting /page (1st time)
Nginx
Shared memory
1
2
3
4
/page
/page

Requesting /page SLIC subrequests (1st time)
Nginx
1
2
3
/menu
/news
/top (with session cookie)
/menu
/news
/top (in SLIC session)

Requesting /page (next time)
Nginx
Shared memory 1
2
/page
/page
/menu
/news
/top (in SLIC session)

SLIC on Nginx
<slic:include key="top" src="/top" session="true" />
<slic:include key="news" src="/news" />
<slic:include
key="menu"
src="/menu" />
5 messages ???

New message is sent...
POST /send
DB
insert into...
set(...)
top (in SLIC session)

Advantages
No repeated GET hits to webserver anymore !
At login : POST → warm up the cache !
No repeated hits for user-specific content
Not even for non-specific content

News added
addnews() method
DB
insert into...
set(...)
Memcache key /news

First release : ESI
Part of the ESI 1.0 spec
Only relevant features implemented
Extension for dynamic session support
But : unavailable for copyright reasons

Rebuilt from scratch : SLIC
Control structures : if/else, switch/case, foreach
Variable handling
Strings : concatenation, substring, …
Exception handling, header manipulation, …
JSON support !

SLIC code samples
You are logged in as : <slic:session_var("person_name") />

SLIC code samples
<slic:switch var="session_var('isAdmin')">
<slic:case value="1">
<slic:include key="admin-buttons" src="/admin-buttons.php" />
</slic:case>
<slic:default>
<div id="just-a-user">
<slic:include key="user-buttons" src="/user-buttons.php" />
</div>
</slic:default>
</slic:switch>

SLIC code samples
<slic:foreach item="messageId" src="global_var('thread' + query_var('threadId'))">
<slic:include key="'thread-message_' + messageId"
src="'/thread/message.php?id=' + messageId" />
</slic:foreach>

Approaches – full block
<p id=”LoggedInAs”>
You are logged in as : Wim Godden
</p>
<p id=”MessageCount”>
You have 5 messages
</p>
5 messages
top_432

Approaches – individual variables
You are logged in as : <slic:session_var("person_name") />
</p>
You have <slic:session_var(“messages”) /> messages
</p>
5 messages

Approaches – JSON
5 messages
You are logged in as : <slic:session_var("userData").person_name />
</p>
You have <slic:session_var(“userData”).message_count /> messages
</p>

Identifying the user
In Nginx configuration :
slic_session_cookie <name> → Defined by language (or configurable)
slic_session_identifier <string> → Defined by you
Example for PHP :
slic_session_cookie PHPSESSID
slic_session_identifier UserID

Identifying the user
Cookie :
PHPSESSID =
jpsidc1po35sq9q3og4f3hi6e2
Nginx + SLIC
4g3e2t UserID_jpsidc1po35sq9q3og4f3hi6e2

Retrieving user specific content
Nginx + SLIC
get userData_432
Cookie :
PHPSESSID =
jpsidc1po35sq9q3og4f3hi6e2

Figures
2nd customer :
No. of web servers : 72 → 8
No. of db servers : 15 → 4
Total : 87 → 12 (86% reduction !)
Last customer :
No. of total servers : +/- 1350
Expected reduction : 1350 → 380
Expected savings : €1.5 Million per year

Code changes
Required
Template conversion
Push-to-DB → Push-to-DB + Push-to-Cache
Choice :
If user is logged in → push updates to cache
If user is not logged in → warm up cache on login

Availability
Good news :
The concept is solid : ESI version stable at 4 customers
Open Source
Bad news :
First customer holds copyrights
Total rebuild
Q2 2015 : v0.1 (include, variable handling, …)
Final release : Q3 2015
Site : http://slic.cu.be
Code : Github

Some technical details
Written in Lua (with LuaJIT)
Each SLIC:include is a subrequest
Groups cache key requests together for multiget
Shares cache results across all subrequests
Memcached implemented
Redis and others in the pipeline
Not RFC compliant yet
Unit tested
Future (1.0 or beyond) :
Better cache abstraction
Template compilation
Translation functionality
...

When dynamic becomes static - the next step in web caching techniques

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