Varnish Cache

Northeast PHP August 12, 2012Varnish, The Good, The Awesome, and the Downright Crazy By Mike Willbanks Sr. Web Architect Manager NOOK Developer

Housekeeping… • Talk   Slides will be online later! • Me   Sr. Web Architect Manager at NOOK Developer   Prior MNPHP Organizer   Open Source Contributor (Zend Framework and various others)   Where you can find me: • Twitter: mwillbanks G+: Mike Willbanks • IRC (freenode): mwillbanks Blog: http://blog.digitalstruct.com • GitHub: https://github.com/mwillbanks2

Agenda • What is Varnish • The Good : Why…   The quick, easy and hardly informed way… • The Awesome : How…   VCL’s, Directors and more… • The Crazy : Go…   ESI, Purging, VCL C, and VMOD… • Varnish Command Line Apps   varnishtop, varnishstat, etc.3

What is Varnish?Official StatementWhat the hell it meansGraphs, oh my!

Official Statement “Varnish is a web application accelerator. You install it in front of your web application and it will speed it up significantly.”5

What The Hell? Tell me! • Varnish allow you to accelerate your website   By using memory and keeping in mind cookies, request headers and more… • It caches pages so that your web server can RELAX!   What about my apache, tomcat, nginx and (mongrel|thin| goliath….)   Generally caching by TTL + HTTP Headers (cookies too!) • A load banancer, proxy and more…   What? …. Yes, it can do that!6

A General Use Case • CaringBridge Status Server   Getting a message to mobile users.   The system is down, or we want to be able to communicate a message to them about some subject… maybe a campaign.   The apps and mobile site rely on an API • Trouble in paradise? Few and far in between.   Let an API talk to a server…   A story on crashing and burning before varnish.7

The Graph - AWS Req/s Peak Load700 14600 12500 10400 8300 Req/s Peak Load 6200 4100 2 0 0 Small X-Large Small Varnish Small X-Large Small Varnish Time Requests500 80000450 70000400 60000350300 50000250 40000 Time Requests200 30000150 20000100 50 10000 0 0 8 Small X-Large Small Varnish Small X-Large Small Varnish

The Raw Data Small X-‐Large Small Varnish Concurrency 10 150 150 Requests 5000 55558 75000 Time 438 347 36 Req/s 11.42 58 585 Peak Load 11.91 8.44 0.35 19,442 Comments failed reqs 9

The Good – Listen Up!InstallmentDocumentationFinding Existing VCL’s

Installment • RTM : http://goo.gl/hl4Tt   Debian: sudo apt-get install varnish   EPEL: yum install varnish • only 6.x otherwise you’ll be out of date!   WOOT Compiling #git • git clone git://git.varnish-cache.org/varnish-cache • cd varnish-cache • sh autogen.sh • ./configure • make && make install11

Varnish Daemon • varnishd   -a address[:port] listen for client   -b address[:port] backend requests   -T address[:port] administration http   -s type[,options] storage type (malloc, file, persistence)   -P /path/to/file PID file   Many others; these are generally the most important. Generally the defaults will do with just modification of the default VCL (more on it later).12

Documentation • Reference Manual   https://www.varnish-cache.org/docs/3.0/reference/index.html • Tutorial – more like a book version of the reference manual   https://www.varnish-cache.org/docs/3.0/tutorial/index.html • Knock yourselves out! There is a ton of documentation • Yes, this makes happy developers.   Documentation is very accurate, read carefully.   Focus heavily on VCL’s, that is generally what you need.   I’m attempting to show you some of how this works but you will require the documentation to assist you.13

Existing VCL’s – The truly lazy… • VCL’s are available for common open source projects   Hi wordpress and drupal! • https://www.varnish-cache.org/trac/wiki/VarnishAndWordpress • https://www.varnish-cache.org/trac/wiki/VarnishAndDrupal   Examples of all sorts of crazy • https://www.varnish-cache.org/trac/wiki/VCLExamples14

Wordpress = Bad Slashdot Bad!!! backend default { .host = "127.0.0.1“; .port = "8080"; } sub vcl_recv { if (!(req.url ~ "wp-(login|admin)")) { unset req.http.cookie; } } sub vcl_fetch { if (!(req.url ~ "wp-(login|admin)")) { unset beresp.http.set-cookie; } }15

The Awesome – Going PlacesVCLDirectorsA Few Examples

VCL’s by Diagram…17

VCL – Varnish Configuration Language • VCL State Engine   Each Request is Processed Separately & Independently   States are Isolated but are Related   Return statements exit one state and start another   VCL defaults are ALWAYS appended below your own VCL • VCL can be complex, but…   Two main subroutines; vcl_recv and vcl_fetch   Common actions: pass, hit_for_pass, lookup, pipe, deliver   Common variables: req, beresp and obj   More subroutines, functions and complexity can arise dependent on condition.18

VCL – Subroutines – breaking it down. • vcl_init – VCL is loaded, no request yet; VMOD initialization • vcl_recv – Beginning of request, req is in scope • vcl_pipe – Client & backend data passed unaltered • vcl_pass – Request goes to backend and not cached • vcl_hash – call hash_data to add to the hash • vcl_hit – called on request found in the cache • vcl_miss – called on request not found in the cache • vcl_fetch – called on document retrieved from backend • vcl_deliver – called prior to delivery of cached object • vcl_error – called on errors19 • vcl_fini – all requests have exited VCL, cleanup of VMOD’s

VCL - Variables • Always Available • Backend Req Prepartion   now – epoch time   bereq – backend request • Backend Declarations • Retrieved Backend Request   .host – hostname / IP   beresp – backend response   .port – port number • Cached Object • Request Processing   obj – Cached object, can only   client – ip & identity change .ttl   server – ip & port • Response Preparation   req – request information   resp – http stuff20

VCL - Functions • hash_data(string) – adds a string to the hash input.   Request host and URL is default from the default vcl. • regsub(string, regex, sub) – substitution on first occurance   sub can contain numbers 0-n to inject matches from the regex. • regsuball(string, regex, sub) – substitution on all occurances • ban(expression) – Ban all objects in cache that match • ban(regex) – Ban all objects in cache that have a URL match21

Directors • Directors allow you to talk to the backend servers • Directors are a glorified reverse proxy   Allows for certain types of load balancing   Allows for talking to a cluster “A director is a logical group of backend servers clustered together for redundancy. The basic role of the director is to let Varnish choose a backend server amongst several so if one is down another can be used.”22

Directors – The Types • Random Director – picks a backend by random number • Client Director – picks a backend by client identity • Hash Director – picks a backend by URL hash value • Round-Robin Director – picks a backend in order • DNS Director – picks a backend by means of DNS   Random OR Round-Robin • Fallback – picks the first “healthy” backend23

Director - Probing • To ensure healthy backends, you need to use probing.   It really sounds like a colonoscopy for servers; which it is. • Variables   .url   .request   .window   .threshold   .intial   .expected_response   .interval   .timeout24

Example VCL Configuration25

The CrazyESI – Edge-Side IncludesPurgingVMOD

ESI – Edge Side Includes • ESI is a small markup language much like SSI (server side includes) to include fragments (or dynamic content for that matter). • Think of it as replacing regions inside of a page as if you were using XHR (AJAX) but single threaded. • Three Statements can be utilized.   esi:include – Include a page   esi:remove – Remove content    - ESI disabled, execute normally27

ESI – By Diagram28

Using ESI • In vcl_fetch, you must set ESI to be on   set beresp.do_esi = true;   By default, ESI will still cache, so add an exclusion if you need it • if (req.url == “/show_username.php”) { return (pass); } • This is a good thing, you may want to cache user information to the right people (aka by cookie value) so that you don’t reload it on every request.   Varnish refuses to parse content for ESI if it does not look like XML • This is by default; so check varnishstat and varnishlog to ensure that it is functioning like normal.29

ESI – By Example <html> <head><title>Rock it with ESI</title></head> <body> <header> <esi:include src="/user_header.php" />   </header> <section id="main"></section <footer></footer> </body> </html>30

Purging • The various ways of purging   varnishadm – command line utility • It’s the ole finger in the back of the throat   Sockets (port 6082) – everyone likes a good socket wrench • Sure, Ipecac is likely overkill.   HTTP – now that is the sexiness • A few headers, nothing forced.31

Purging Examples varnishadm -T 127.0.0.1:6082 purge req.url == "/foo/bar“ telnet localhost 6082 purge req.url == "/foo/bar telnet localhost 80 Response: Trying 127.0.0.1... Connected to localhost. Escape character is ^]. PURGE /foo/bar HTTP/1.0 Host: bacon.org32

Distributed Purging • Distributed Purging… like a sorority party.   Use a message queue (or gearman job server)   Have a worker that knows about the varnish servers   Submit the request to clear the cache in the asynchronously or synchronously depending on your use case. • Have enough workers to make this effective at purging the cache quickly.   This will make it far easier to scale; you can either store the servers in a config file, database or anything else you think is relevant.33

Embedding C in VCL – you must be crazy • Before getting into VMOD; did you know you can embed C into the VCL for varnish? • Want to do something crazy fast or leverage a C library for pre or post processing? • I know… you’re thinking that’s useless..   On to the example; and a good one from the Varnish WIKI!34

VCL - Embedded C for syslog – uber sexy C{ #include <syslog.h> }C sub vcl_something { C{ syslog(LOG_INFO, "Something happened at VCL line XX."); }C } # Example with using varnish variables C{ syslog(LOG_ERR, "Spurious response from backend: xid %s request %s %s "%s" %d "%s" "%s"", VRT_r_req_xid(sp), VRT_r_req_request(sp), VRT_GetHdr(sp, HDR_REQ, "005host:"), VRT_r_req_url(sp), VRT_r_obj_status(sp), VRT_r_obj_response(sp), VRT_GetHdr(sp, HDR_OBJ, "011Location:")); }C35

VMOD – Varnish Modules / Extensions • Taking VCL embedded C to the next level • Allows you to extend varnish and create new functions • Now, if you are writing modules for varnish you have a specialty use case!   Go read up on it!   https://www.varnish-cache.org/docs/trunk/reference/vmod.html36

VMOD - std • The VMOD std is shipped with varnish; it provides some useful commands   toupper   syslog   tolower   fileread   set_up_tos   duration   random   integer   log   collect37

Varnish Command Line Appsvarnish varnishadm varnishhistvarnishlog varnishncsa varnishreplayvarnishsizes varnishstat varnishtest varnishtop

What is Varnish doing… • What is varnish doing right now? • How do I debug what is happening?   varnishtop39

What is Varnish doing…40

Logging • Many times people want to log the requests to a file   By default Varnish only stores these in shared memory.   Apache Style Logs • varnishncsa –D –a –w log.txt   This will run as a daemon to log all of your requests on a separate thread.41

Logging42

Cache Warmup • Need to warm up your cache before putting a sever in the queue or load test an environment?   varnishreplay –r log.txt • Replaying logs can allow you to do this. This is great for when you are going to be deploying code to check for performance issues.   Although… be careful so that you don’t POST data or create data on peoples accounts. Maybe cat the file and remove anything that executes on data.43

Cache Hit Ratios? No Problem • How to see your cache hit ratios…   varnishstat • Want to parse them from XML so you can create a sexy administration panel?   varnishstat –x44

Cache Hit Ratios? No Problem45

Questions?These slides will be posted to SlideShare & SpeakerDeck.  SpeakerDeck: http://speakerdeck.com/u/mwillbanks  Slideshare: http://www.slideshare.net/mwillbanks  Twitter: mwillbanks  G+: Mike Willbanks  IRC (freenode): mwillbanks  Blog: http://blog.digitalstruct.com  GitHub: https://github.com/mwillbanks

Varnish Cache

by Mike Willbanks on Aug 12, 2012

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