caching on the edge

Speaker | Company

Title // Presentation Name

Caching on the Edge Fabien Potencier

Who are you?

May 1996

RFC1945 – HTTP/1.0

March 1999

RFC2616 – HTTP/1.1

http://www.ietf.org/rfc/rfc2616.txt

HTTP Bis – Work in progress

http://tools.ietf.org/wg/httpbis/

http://www.flickr.com/photos/visualpanic/233508614

p1: Messaging: Low-level message parsing and connection management p2: Semantics: Methods, status codes and headers p3: Payload: Dealing with content, message-specific headers p4: Conditional Requests: e.g., If-Modified-Since p5: Range Requests: Getting partial content p6: Caching: Browser and intermediary caches p7: Authentication: HTTP authentication framework

The Client sends a Request to the Server The Server sends back a Response to the Client

A Client (browser, bot, WS, curl, …) A Server (Apache, nginx, …)

The Request and the Response are HTTP messages

Let’s play with HTTP and HTTP headers

GET / HTTP/1.1 Host: http.trainings.sensiolabs.com

« The request-header fields allow the client to pass additional information about the request, and about the client itself, to the

server. These fields act as request modifiers, with semantics equivalent to the parameters on a programming language method

invocation. »

« Each HTTP header field consists of a case-insensitive field name followed by a colon (":"), optional whitespace, and the field value »

HTTP/1.1 200 OK Date: Wed, 15 Oct 2005 07:07:07 GMT Server: Apache Content-Length: 14 Content-Type: text/html

Hello World!

Live HTTP headers Firefox extension

http://livehttpheaders.mozdev.org/

$ curl -i http://http.trainings.sensiolabs.com/

Hello World!

$ telnet localhost 80 Trying ::1... Connected to localhost. Escape character is '^]'. GET / HTTP/1.1 Host: http.trainings.sensiolabs.com

Hello World!

Connection closed by foreign host.

HTTP Headers with PHP

header('Content-Type: text/plain');

header('content-type: text/plain');

Caching in the HTTP Specification

p1: Messaging: Low-level message parsing and connection management p2: Semantics: Methods, status codes and headers p3: Payload: Dealing with content, message-specific headers p4: Conditional Requests: e.g., If-Modified-Since p5: Range Requests: Getting partial content p6: Caching: Browser and intermediary caches p7: Authentication: HTTP authentication framework

HTTP Expiration HTTP Validation

Fresh vs Stale

HTTP Headers for Expiration

Cache-Control

Expires

HTTP Headers for Validation

Last-Modified / If-Modified-Since

ETag / If-None-Match

HTTP Cache headers only work with “safe” HTTP methods

(like GET & HEAD)

Never change the state of the server when serving a GET request

(we are talking about the application’s state of course, you can log, cache, …)

HTTP Expiration

Expires

« The "Expires" header field gives the date/time after which

the response is considered stale. »

Your PHP application

GET /foo HTTP/1.1 Host: foo.org

HTTP/1.1 200 OK Expires: Thu, 01 Dec …

GET /foo HTTP/1.1 200 OK Expires: Thu, 01 Dec …

Before expira4on

Your applica4on is not called

A<er expira4on

Not fresh

Expires: Thu, 01 Dec 2010 16:00:00 GMT

Date in RFC1123 format, not RFC2822 (timezone always GMT, which is ~ UTC)

$expires = gmdate('D, j M Y H:i:s T', time() + 5);

header('Expires: '.$expires);

$date = new DateTime(null, new DateTimeZone('UTC')); $date->modify('+5 seconds');

$expires = $date->format('D, d M Y H:i:s').' GMT';

$date = gmdate('D, j M Y H:i:s T', time() + 5);

header('Expires: '.$expires);

$date->setTimezone(new DateTimeZone('UTC'));

/expires_with_expires_in_5s.php

WARNING

The clocks on the Web server AND the cache (aka browser)

MUST be synchronised

WARNING

« HTTP/1.1 servers SHOULD NOT send Expires dates

more than one year in the future. »

Mostly useful to make static assets (images, css, js, …) cacheable with an extremely long expiry time

But there is a better way!

Use Cache-Control instead

header('Cache-Control: max-age=5');

http.trainings.sensiolabs.com/expires_in_5s.php

Don’t use Expires Use Cache-Control

…except if you want to set a date, which should be pretty rare

HTTP Validation

“304 Not Modified” is your friend

Etag / If-None-Match

GET /foo HTTP/1.1 200 OK ETag: abcdef …

HTTP/1.1 200 OK ETag: abcdef

GET /foo HTTP/1.1 Host: foo.org If-None-Match: abcdef

HTTP/1.1 304 Not Modified

HTTP/1.1 200 OK ETag: abcdef

If the resource has not changed

If the resource has changed

GET /foo HTTP/1.1 200 OK ETag: 123456 …

HTTP/1.1 200 OK ETag: 123456

// compute ETag value $etag = '...';

if ( isset($_SERVER['HTTP_IF_NONE_MATCH']) && $_SERVER['HTTP_IF_NONE_MATCH'] == $etag ) { header('HTTP/1.1 304 Not Modified'); } else { header('ETag: '.$etag); echo 'Hello'; }

This is a simple but naïve implementation…

Last-Modified / If-Modified-Since

GET /foo HTTP/1.1 200 OK Last-Modified: Thu, …

HTTP/1.1 200 OK Last-Modified: Thu, …

GET /foo HTTP/1.1 Host: foo.org If-Modified-Since: Thu,

HTTP/1.1 304 Not Modified

GET /foo HTTP/1.1 200 OK Last-Modified: Thu, …

HTTP/1.1 200 OK Last-Modified: Thu, …

If the resource has not changed

GET /foo HTTP/1.1 200 OK Last-Modified: Thu,…

GET /foo HTTP/1.1 200 OK Last-Modified: Sun,…

GET /foo HTTP/1.1 Host: foo.org If-Modified-Since: Thu,

If the resource has changed

HTTP/1.1 200 OK Last-Modified: Sun, …

Expiration & Validation

GET /foo HTTP/1.1 200 OK Etag: abcdef Cache-‐Control: max-‐age=10 …

HTTP/1.1 200 OK ETag: abcdef Cache-‐Control: max-‐age=10

Before expira4on

Your applica4on is not called

HTTP/1.1 304 Not Modified Cache-‐Control: max-‐age=10

A<er expira4on but resource s4ll valid

You can combine HTTP headers the way you want

Expiration wins over Validation

Expiration allows you to scale as less requests hit your server (and client speed is better too)

Validation saves bandwidth

The goal is to never generate the same response twice

PHP and Cache HTTP headers

session_start(); $_SESSION['foo'] = 'bar';

echo 'Hello';

http.trainings.sensiolabs.com/index.php

http.trainings.sensiolabs.com/cookie.php

Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0

Kinds of caches

Browser Cache

On the server side

in a Com

On the server side

Your PHP application Br

Proxy Cache

On the server side

in a Com

On the server side

in a Com

Gateway Cache

On the server side

in a Com

On the server side

On the server side W

ithin a Com

Gateway Cache Reverse Proxy Cache

Surrogate Cache HTTP Accelerator

Browser

Browser Cache

Proxy Cache

Browser Cache

Local cache for when you hit “back” or

when images are reused throughout a website

Proxy Cache

A shared cache Many people behind a single proxy

Installed by large corporations and ISPs Reduce latency and network traffic

Gateway Cache

A shared cache on the server side Installed by network administrators

Make websites more scalable, reliable and performing better

CDNs like Akaïma are gateway caches

Today, we will mainly talk about Gateway caches

Edge Caching

App Browser

Browser

Gateway Cache

HTTP 1.1 allows caching anything by default unless explicit Cache-Control header

In practice, most caches avoid anything with

Cache-Control Cookie / Set-Cookie

WWW-Authenticate / Authorization POST / PUT

302 / 307 status codes

Cache-Control: private

This is the default with PHP when you have a session Browser cache will still work fine here

(public means shared caches, private means browser cache)

A gateway cache won't cache anything "private" or carrying a cookie

In a real-world: tracking cookies (Google Analytics)

All proxies do caching based on the same HTTP headers

We need several clients to understand how it works and how the cached is shared

HTTP Expiration

Bob’s

GET /foo HTTP/1.1 200 OK C-C: max-age=600 …

HTTP/1.1 200 OK C-C: max-age=600

Bob’s

HTTP Validation

Bob’s

GET /foo HTTP/1.1 200 OK Etag: abcde …

HTTP/1.1 200 OK Etag: abcde

GET /foo HTTP/1.1 200 OK Etag: abcde …

HTTP/1.1 200 OK Etag: abcde

Bob’s

GET /foo HTTP/1.1 Host: foo.org If-None-Match: ab

GET /foo HTTP/1.1 200 OK Etag: ab …

HTTP/1.1 200 OK Etag: ab

304 Not Modified 304 Not Modified

GET /foo HTTP/1.1 Host: foo.org If-None-Match: ab

304 Not Modified

Gateway caches

Varnish (only does that and tries to do it well) Squid (just one way to use it)

mod_cache (Apache)

Gateway caches are a great way to make your website performs better

But what if you cannot cache whole pages? What if a page has "more" dynamic parts?

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cacheable for 10 seconds cacheable for 5 seconds

ESI… or Edge Side Includes

http://www.w3.org/TR/esi-lang

<esi:include src="..." />

<esi:include src="http://..." />

GET /bar HTTP/1.1 Host: foo.org

Lorem ipsum dolor

<esi:include src="hYp.." />

HTTP/1.1 200 OK

Lorem ipsum dolor

HTTP/1.1 200 OK

Lorem ipsum dolor sit amet,

Lorem ipsum dolor

HTTP/1.1 200 OK

Lorem ipsum dolor

HTTP/1.1 200 OK

Your PHP application GET /foo HTTP/1.1 Host: foo.org

Lorem ipsum dolor

HTTP/1.1 200 OK

Lorem ipsum dolor

HTTP/1.1 200 OK

GET /foo C-C: max-age=10

Lor <esi:include />

GET /bar C-C: max-age=5

Lor Lorem

Lorem ipsum dolor

HTTP/1.1 200 OK

Lor <esi:include />

Lor Lorem 2 seconds later…

Lorem ipsum dolor

HTTP/1.1 200 OK

Lor <esi:include />

Lor Lorem 7 seconds later…

Cache-Control: max-age=10

Cache-Control: s-maxage=10

Lorem ipsum dolor

HTTP/1.1 200 OK C-C: s-maxage=10

Lorem ipsum dolor

HTTP/1.1 200 OK

Lorem ipsum dolor

HTTP/1.1 200 OK

GET /foo C-C: s-maxage=10

Lor <esi:include />

GET /bar C-C: s-maxage=5

Lorem ipsum dolor

HTTP/1.1 200 OK

Lorem ipsum dolor

HTTP/1.1 200 OK

Lor <esi:include />

2 seconds later…

Lorem ipsum dolor

HTTP/1.1 200 OK

Lorem ipsum dolor

HTTP/1.1 200 OK

Lor <esi:include />

7 seconds later…

Lorem ipsum dolor sit amet, consectetur adipiscing elit. In vel nulla arcu, vitae cursus nunc. Integer semper turpis et enim porRtor iaculis. Nulla facilisi. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris vehicula ves4bulum dictum. Aenean non velit tortor. Nullam adipiscing malesuada aliquam.

Lorem ipsum dolor sit amet, consectetur adipiscing elit. In vel nulla arcu, vitae cursus nunc.

main template

layout

base layout

included page included page

included page

sub vcl_fetch { esi; }

varnishlog -i TxURL

varnishlog –o VCL_call hit | grep RxURL

Make your application work when ESI is enabled and when it’s not

And only parse for ESIs when it’s needed

Surrogate-Capability

Surrogate-Control

http://www.w3.org/TR/edge-arch

Surrogate-Capability: abc="Surrogate/1.0 ESI/1.0"

Surrogate-Control: content="ESI/1.0"

RewriteEngine On RewriteRule ^(.*)$ index.php [QSA,L]

sub vcl_recv { set req.http.Surrogate-Capability = "abc=ESI/1.0"; }

sub vcl_fetch { if (beresp.http.Surrogate-Control ~ "ESI/1.0") { unset beresp.http.Surrogate-Control; esi; } }

function has_surrogate_ESI_capability() { return isset($_SERVER['HTTP_SURROGATE_CAPABILITY']) && preg_match('#ESI/1.0#', $_SERVER['HTTP_SURROGATE_CAPABILITY']); }

function add_surrogate_control() { header('Surrogate-Control: content="ESI/1.0"'); }

function include($path) { if (has_surrogate_ESI_capability()) { $path = get_absolute_path($path);

echo '<esi:include src="'.$path.'" />';

add_surrogate_control(); } else { include dirname(__FILE__).'/'.$path; } }

Imagine the power when you combine ESI, expiration, validation, max-age, s-maxage, …

Why would you want to reinvent the wheel? and implement your own caching system?

Because you cannot afford to use Varnish? Because you use a shared hosting company?

// With the Symfony2 HTTP accelerator instead of Varnish // won't work if you use exit() for instance... // won't work if you have "global" state // This is just a skeleton to get you started

// Of course, this is native with Symfony2 ;)

use Symfony\Component\HttpFoundation\Response; use Symfony\Component\HttpFoundation\Request; use Symfony\Component\HttpKernel\HttpKernelInterface; use Symfony\Component\HttpKernel\Cache\Cache; use Symfony\Component\HttpKernel\Cache\Esi; use Symfony\Component\HttpKernel\Cache\Store;

class AppKernel implements HttpKernelInterface { public function handle(Request $request = null, $type = HttpKernelInterface::MASTER_REQUEST, $raw = false) { return new Response($content, 200, $headers); }

public function getRequest() {} }

$_SERVER['HTTP_SURROGATE_CAPABILITY'] = 'symfony2="ESI/1.0"';

// quick hack... not secure at all! $base = str_replace('index.php', '', $request->getScriptName()); $script = str_replace($base, '', $request->getRequestUri());

ob_start();

include __DIR__.'/'.$script;

$content = ob_get_clean(); $headers = array(); foreach (headers_list() as $header) { $elements = explode(':', $header, 2); $headers[$elements[0]] = trim($elements[1]); }

// do not deal with response others than 200 // implementation depends on your code return new Response($content, 200, $headers);

$kernel = new AppKernel(); $store = new Store('/path/to/http_cache'); $esi = new Esi();

$cache = new Cache($kernel, $store, $esi); $cache->handle()->send();

error_log($cache->getLog());

Goal Be as dynamic as needed

Hit the application as less as possible

The power is even bigger than what you think…

<esi:include src="http://...” alt="http://...” onerror="continue" />

stale-while-revalidate - rfc5861

stale-if-error - rfc5861

There are only two hard things in Computer Science: cache invalidation and naming things. -- Phil Karlton

http://martinfowler.com/bliki/TwoHardThings.html

PURGE: varnishadm -T localhost:6082 purgeurl "^/images/ »

acl purge_acl { "localhost"; "1.2.3.4"; }

sub vcl_recv { if (req.request == "PURGE") { if (!client.ip ~ purge_acl) { error 405 "Not allowed."; } purge_url(req.url); error 200 "Purged."; }

return(lookup); }

curl -X PURGE http://...

WARNING

Don't use GZIP with ESI as Varnish won't be able to assemble the page

caching on the edge

foo http1

abcdef http1

abcdef hello http1

rfc2616 http1

rfc1945 http1

ok date

progress http

orgwghttpbis http

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