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Varnish, The Good, The Awesome, and the Downright Crazy

Varnish, The Good, The Awesome, and the Downright Crazy

Getting started with Varnish; all of the crazy awesome sauce that makes varnish scale your website.


Mike Willbanks

April 07, 2012

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  1. Varnish, The Good, The Awesome, and the Downright Crazy By

    Mike Willbanks Software Engineering Manager CaringBridge MinneBar April 7, 2012
  2. 2 •Talk  Slides will be online later! •Me 

    Software Engineering Manager at CaringBridge  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/mwillbanks Housekeeping…
  3. 3 • What the … is Varnish? • The Good

     “I don’t want to listen to you but only want to play on my laptop.”  The quick, easy and uninformed way... You listening over there? • The Awesome  VCL’s, Directors and more… now we’re going places. • The Crazy  ESI, Purging, VCL C, and VMOD… my head hurts, stop! • Varnish Command Line Apps  varnishtop, varnishstat, etc. • Questions  Although you can bring them up at anytime! Agenda
  4. What the… is Varnish? Official Statement What the hell it

    means Graphs, oh my!
  5. 5 “Varnish is a web application accelerator. You install it

    in front of your web application and it will speed it up significantly.” Official Statement
  6. 6 •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, uhhh… (mongrel|thin|goliath….)  Generally caching by TTL + HTTP Headers (cookies too!) •A load banancer, proxy and more…  What? …. Yes, it can do that! #winning What The Hell? Tell me!
  7. 7 •CaringBridge Status Server  We need to get a

    message to our 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. • We want to talk to our users? Of course!  Let an API talk to a server…  A story on crashing and burning  A story on a bad thing making a huge success! A General Use Case
  8. 8 The Graph - AWS 0 10000 20000 30000 40000

    50000 60000 70000 80000 Small X-Large Small Varnish Requests Requests 0 50 100 150 200 250 300 350 400 450 500 Small X-Large Small Varnish Time Time 0 100 200 300 400 500 600 700 Small X-Large Small Varnish Req/s Req/s 0 2 4 6 8 10 12 14 Small X-Large Small Varnish Peak Load Peak Load
  9. 9 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 Comments 19,442 failed reqs
  10. The Good – Listen Up! Installment Documentation Finding Existing VCL’s

  11. 11 •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 #winning #git • git clone git://git.varnish-cache.org/varnish-cache • cd varnish-cache • sh autogen.sh • ./configure • Make && make install Installment
  12. 12 •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. Documentation
  13. 13 •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/VCLExamples Existing VCL’s – The truly lazy…
  14. 14 backend default { .host = "“; .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; } } Wordpress = Bad Slashdot Bad!!!
  15. The Awesome – Going Places VCL Directors A Few Examples

  16. 16 Mind ****

  17. 17 •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. VCL – Varnish Configuration Language
  18. 18 • 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 errors • vcl_fini – all requests have exited VCL, cleanup of VMOD’s VCL - Subroutines
  19. 19 • Always Available  now – epoch time •

    Backend Declarations  .host – hostname / IP  .port – port number • Request Processing  client – ip & identity  server – ip & port  req – request information VCL - Variables • Backend Req Prepartion  bereq – backend request • Retrieved Backend Request  beresp – backend response • Cached Object  obj – Cached object, can only change .ttl • Response Preparation  resp – http stuff
  20. 20 • 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 match VCL - Functions
  21. 21 • 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.” Directors
  22. 22 •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” backend Directors – The Types
  23. 23 •To ensure healthy backends, you need to use probing.

     It really sounds like a colonoscopy for servers. •Variables  .url  .request  .window  .threshold  .intial  .expected_response  .interval  .timeout Director - Probing
  24. 24 Example VCL Configuration

  25. The Crazy ESI – Edge-Side Includes Purging VMOD

  26. 26 •ESI is a small markup language much like SSI

    (server side includes) to include fragments (or dynamic content for that matter). •If don’t think you can use varnish because you have say, user information displayed on every page; think again! •Think of it as replacing regions inside of a page as if you were using XHR (AJAX). •Three Statements are Implemented  esi:include – Include a page  esi:remove – Remove content  <!-- esi --> - ESI disabled, execute normally ESI – Edge Side Includes
  27. 27 ESI – By Diagram

  28. 28 •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); }  Varnish refuses to parse content for ESI if it does not look like XML • This is by default; so check varnishstat and varnishlog Using ESI
  29. 29 <html> <head><title>Rock it with ESI</title></head> <body> <header> <esi:include src="/user_header.php"

    /> <!-- Don't do this as you'd lose the advantage of varnish --> <!--esi <?php include 'user_header.php'; ?> --> </header> <section id="main"></section <footer></footer> </body> </html> ESI – By Example
  30. 30 •Sometimes, you just need to purge.  Don’t drink

    too much tonight, ok? • If you do… find a DD or a cab. •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 • See, now we’re not forcing the point! Purging – Beer anyone?
  31. 31 varnishadm -T purge req.url == "/foo/bar“ telnet localhost

    6082 purge req.url == "/foo/bar telnet localhost 80 Response: Trying Connected to localhost. Escape character is '^]'. PURGE /foo/bar HTTP/1.0 Host: bacon.org Purging Examples
  32. 32 •Distributed Purging… now that’s a punch line!  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. Sexy Purging
  33. 33 •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! Embedding C in VCL – you must be crazy
  34. 34 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:")); }C VCL - Embedded C for syslog – uber sexy
  35. 35 •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.html VMOD – Varnish Modules / Extensions
  36. 36 •The VMOD std is shipped with varnish; it provides

    some useful commands  toupper  tolower  set_up_tos  Random  Log VMOD - std  syslog  fileread  duration  integer  collect
  37. Varnish Command Line Apps varnish varnishadm varnishhist varnishlog varnishncsa varnishreplay

    varnishsizes varnishstat varnishtest varnishtop
  38. 38 •What is varnish doing right now? •How do I

    debug what is happening?  varnishtop What is Varnish doing…
  39. 39 •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 Logging
  40. 40 •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. Cache Warmup
  41. 41 •How to see your cache hit ratios…  varnishstat

    •Want to parse them from XML?  varnishstat –x Cache Hit Ratios? No Problem
  42. Questions? These slides will be posted to SlideShare & SpeakerDeck.

    Slideshare: http://www.slideshare.net/mwillbanks SpeakerDeck: http://speakerdeck.com/u/mwillbanks Twitter: mwillbanks G+: Mike Willbanks IRC (freenode): mwillbanks Blog: http://blog.digitalstruct.com GitHub: https://github.com/mwillbanks