Varnish, The Good, The Awesome, and the Downright Crazy.
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This document summarizes Mike Willbanks' presentation on Varnish to the MinneBar group on April 7, 2012. The presentation covered an introduction to Varnish including what it is and how it works, the benefits of using Varnish to accelerate websites ("The Good"), more advanced Varnish features like VCL and directors ("The Awesome"), and complex Varnish configurations involving ESI, purging, and embedding C code in VCL ("The Crazy"). It also provided overviews of various Varnish command line applications for monitoring and debugging Varnish like varnishtop, varnishstat, and varnishlog.
![Purging Examples
varnishadm -T 127.0.0.1:6082 purge req.url == "/foo/barâ
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.org
31](https://image.slidesharecdn.com/minnedemovarnish-120407205741-phpapp02/85/Varnish-The-Good-The-Awesome-and-the-Downright-Crazy-31-320.jpg)
Varnish, The Good, The Awesome, and the Downright Crazy.
- 1. MinneBar April 7, 2012 Varnish, The Good, The Awesome, and the Downright Crazy By Mike Willbanks Software Engineering Manager CaringBridge
- 2. Housekeeping⌠⢠Talk ď´ Slides will be online later! ⢠Me ď´ Software Engineering Manager at CaringBridge ď´ MNPHP Organizer ď´ Open Source Contributor (Zend Framework and various others) ď´ Where you can find me: ⢠Twitter: mwillbanks G+: Mike Willbanks ⢠IRC (freenode): mwillbanks Blog: http://blog.digitalstruct.com ⢠GitHub: https://github.com/mwillbanks 2
- 3. Agenda ⢠What the ⌠is Varnish? ⢠The Good ď´ âI donât want to listen to you but only want to play on my laptop.â ď´ The quick, easy and uninformed way... You listening over there? ⢠The Awesome ď´ VCLâs, Directors and more⌠now weâre going places. ⢠The Crazy ď´ ESI, Purging, VCL C, and VMOD⌠my head hurts, stop! ⢠Varnish Command Line Apps ď´ varnishtop, varnishstat, etc. ⢠Questions ď´ Although you can bring them up at anytime! 3
- 4. What the⌠is Varnish? Official Statement What the hell it means Graphs, oh my!
- 5. Official Statement âVarnish is a web application accelerator. You install it in front of your web application and it will speed it up significantly.â 5
- 6. What The Hell? Tell me! ⢠Varnish allow you to accelerate your website ď´ By using memory and keeping in mind cookies, request headers and more⌠⢠It caches pages so that your web server can RELAX! ď´ What about my apache, tomcat, uhhh⌠(mongrel|thin|goliathâŚ.) ď´ Generally caching by TTL + HTTP Headers (cookies too!) ⢠A load banancer, proxy and moreâŚ ď´ What? âŚ. Yes, it can do that! #winning 6
- 7. A General Use Case ⢠CaringBridge Status Server ď´ We need to get a message to our mobile users! ď´ The system is down, or we want to be able to communicate a message to them about some subject⌠maybe a campaign. ď´ 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! ď´ Let an API talk to a serverâŚ ď´ A story on crashing and burning ď´ A story on a bad thing making a huge success! 7
- 8. The Graph - AWS Req/s Peak Load 700 14 600 12 500 10 400 8 300 Req/s Peak Load 6 200 4 100 2 0 0 Small X-Large Small Varnish Small X-Large Small Varnish Time Requests 500 80000 450 70000 400 60000 350 300 50000 250 40000 Time Requests 200 30000 150 20000 100 50 10000 0 0 8 Small X-Large Small Varnish Small X-Large Small Varnish
- 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 19,442 Comments failed reqs 9
- 10. The Good â Listen Up! Installment Documentation Finding Existing VCLâs
- 11. Installment ⢠RTM : http://goo.gl/hl4Tt ď´ Debian: sudo apt-get install varnish ď´ EPEL: yum install varnish ⢠only 6.x otherwise youâll be out of date! ď´ WOOT Compiling #winning #git ⢠git clone git://git.varnish-cache.org/varnish-cache ⢠cd varnish-cache ⢠sh autogen.sh ⢠./configure ⢠Make && make install 11
- 12. Documentation ⢠Reference Manual ď´ https://www.varnish-cache.org/docs/3.0/reference/index.html ⢠Tutorial â more like a book version of the reference manual ď´ 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. ď´ Documentation is very accurate, read carefully. ď´ Focus heavily on VCLâs, that is generally what you need. ď´ Iâm attempting to show you some of how this works but you will require the documentation to assist you. 12
- 13. Existing VCLâs â The truly lazy⌠⢠VCLâs are available for common open source projects ď´ Hi wordpress and drupal! ⢠https://www.varnish-cache.org/trac/wiki/VarnishAndWordpress ⢠https://www.varnish-cache.org/trac/wiki/VarnishAndDrupal ď´ Examples of all sorts of crazy ⢠https://www.varnish-cache.org/trac/wiki/VCLExamples 13
- 14. Wordpress = Bad Slashdot Bad!!! backend default { .host = "127.0.0.1â; .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; } } 14
- 15. The Awesome â Going Places VCL Directors A Few Examples
- 16. Mind **** 16
- 17. VCL â Varnish Configuration Language ⢠VCL State Engine ď´ Each Request is Processed Separately & Independently ď´ States are Isolated but are Related ď´ Return statements exit one state and start another ď´ VCL defaults are ALWAYS appended below your own VCL ⢠VCL can be complex, butâŚ ď´ Two main subroutines; vcl_recv and vcl_fetch ď´ Common actions: pass, hit_for_pass, lookup, pipe, deliver ď´ Common variables: req, beresp and obj ď´ More subroutines, functions and complexity can arise dependent on condition. 17
- 18. VCL - Subroutines ⢠vcl_init â VCL is loaded, no request yet; VMOD initialization ⢠vcl_recv â Beginning of request, req is in scope ⢠vcl_pipe â Client & backend data passed unaltered ⢠vcl_pass â Request goes to backend and not cached ⢠vcl_hash â call hash_data to add to the hash ⢠vcl_hit â called on request found in the cache ⢠vcl_miss â called on request not found in the cache ⢠vcl_fetch â called on document retrieved from backend ⢠vcl_deliver â called prior to delivery of cached object ⢠vcl_error â called on errors 18 ⢠vcl_fini â all requests have exited VCL, cleanup of VMODâs
- 19. VCL - Variables ⢠Always Available ⢠Backend Req Prepartion ď´ now â epoch time ď´ bereq â backend request ⢠Backend Declarations ⢠Retrieved Backend Request ď´ .host â hostname / IP ď´ beresp â backend response ď´ .port â port number ⢠Cached Object ⢠Request Processing ď´ obj â Cached object, can only ď´ client â ip & identity change .ttl ď´ server â ip & port ⢠Response Preparation ď´ req â request information ď´ resp â http stuff 19
- 20. VCL - Functions ⢠hash_data(string) â adds a string to the hash input. ď´ Request host and URL is default from the default vcl. ⢠regsub(string, regex, sub) â substitution on first occurance ď´ sub can contain numbers 0-n to inject matches from the regex. ⢠regsuball(string, regex, sub) â substitution on all occurances ⢠ban(expression) â Ban all objects in cache that match ⢠ban(regex) â Ban all objects in cache that have a URL match 20
- 21. Directors ⢠Directors allow you to talk to the backend servers ⢠Directors are a glorified reverse proxy ď´ Allows for certain types of load balancing ď´ Allows for talking to a cluster âA 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.â 21
- 22. Directors â The Types ⢠Random Director â picks a backend by random number ⢠Client Director â picks a backend by client identity ⢠Hash Director â picks a backend by URL hash value ⢠Round-Robin Director â picks a backend in order ⢠DNS Director â picks a backend by means of DNS ď´ Random OR Round-Robin ⢠Fallback â picks the first âhealthyâ backend 22
- 23. Director - Probing ⢠To ensure healthy backends, you need to use probing. ď´ It really sounds like a colonoscopy for servers. ⢠Variables ď´ .url ď´ .request ď´ .window ď´ .threshold ď´ .intial ď´ .expected_response ď´ .interval ď´ .timeout 23
- 25. The Crazy ESI â Edge-Side Includes Purging VMOD
- 26. ESI â Edge Side Includes ⢠ESI is a small markup language much like SSI (server side includes) to include fragments (or dynamic content for that matter). ⢠If donât 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 ď´ esi:include â Include a page ď´ esi:remove â Remove content ď´ <!-- esi --> - ESI disabled, execute normally 26
- 27. ESI â By Diagram 27
- 28. Using ESI ⢠In vcl_fetch, you must set ESI to be on ď´ set beresp.do_esi = true; ď´ By default, ESI will still cache, so add an exclusion if you need it ⢠if (req.url == â/show_username.phpâ) { return (pass); } ď´ Varnish refuses to parse content for ESI if it does not look like XML ⢠This is by default; so check varnishstat and varnishlog 28
- 29. ESI â By Example <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> 29
- 30. Purging â Beer anyone? ⢠Sometimes, you just need to purge. ď´ Donât drink too much tonight, ok? ⢠If you do⌠find a DD or a cab. ⢠The various ways of purging ď´ varnishadm â command line utility ⢠Itâs the ole finger in the back of the throat ď´ Sockets (port 6082) â everyone likes a good socket wrench ⢠Sure, Ipecac is likely overkill. ď´ HTTP â now that is the sexiness ⢠See, now weâre not forcing the point! 30
- 31. Purging Examples varnishadm -T 127.0.0.1:6082 purge req.url == "/foo/barâ 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.org 31
- 32. Sexy Purging ⢠Distributed Purging⌠now thatâs a punch line! ď´ Use a message queue (or gearman job server) ď´ Have a worker that knows about the varnish servers ď´ 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. 32
- 33. Embedding C in VCL â 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⌠youâre thinking thatâs useless.. ď´ On to the example; and a good one from the Varnish WIKI! 33
- 34. VCL - Embedded C for syslog â 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:")); }C 34
- 35. VMOD â 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! ď´ Go read up on it! ď´ https://www.varnish-cache.org/docs/trunk/reference/vmod.html 35
- 36. VMOD - std ⢠The VMOD std is shipped with varnish; it provides some useful commands ď´ toupper ď´ syslog ď´ tolower ď´ fileread ď´ set_up_tos ď´ duration ď´ Random ď´ integer ď´ Log ď´ collect 36
- 37. Varnish Command Line Apps varnish varnishadm varnishhist varnishlog varnishncsa varnishreplay varnishsizes varnishstat varnishtest varnishtop
- 38. What is Varnish doing⌠⢠What is varnish doing right now? ⢠How do I debug what is happening? ď´ varnishtop 38
- 39. Logging ⢠Many times people want to log the requests to a file ď´ By default Varnish only stores these in shared memory. ď´ Apache Style Logs ⢠varnishncsa âD âa âw log.txt 39
- 40. Cache Warmup ⢠Need to warm up your cache before putting a sever in the queue or load test an environment? ď´ varnishreplay âr 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. 40
- 41. Cache Hit Ratios? No Problem ⢠How to see your cache hit ratiosâŚ ď´ varnishstat ⢠Want to parse them from XML? ď´ varnishstat âx 41
- 42. Questions? These slides will be posted to SlideShare & SpeakerDeck. ď´Slideshare: http://www.slideshare.net/mwillbanks ď´SpeakerDeck: http://speakerdeck.com/u/mwillbanks ď´Twitter: mwillbanks ď´G+: Mike Willbanks ď´IRC (freenode): mwillbanks ď´Blog: http://blog.digitalstruct.com ď´GitHub: https://github.com/mwillbanks