NGINX High-performance Caching

NGINX High-performance
Caching
Introduced by Andrew Alexeev
Presented by Owen Garrett
Nginx, Inc.

About this webinar
Content Caching is one of the most effective ways to dramatically improve
the performance of a web site. In this webinar, we’ll deep-dive into
NGINX’s caching abilities and investigate the architecture used, debugging
techniques and advanced configuration. By the end of the webinar, you’ll
be well equipped to configure NGINX to cache content exactly as you need.

BASIC PRINCIPLES OF CONTENT CACHING

Basic Principles
Internet
N
GET /index.html
GET /index.html
Used by: Browser Cache, Content Delivery Network and/or Reverse Proxy Cache

Mechanics of HTTP Caching
• Origin server declares cacheability of content
Expires: Tue, 6 May 2014 02:28:12 GMT
Cache-Control: public, max-age=60
X-Accel-Expires: 30
Last-Modified: Tue, 29 April 2014 02:28:12 GMT
ETag: "3e86-410-3596fbbc“
• Requesting client honors cacheability
– May issue conditional GETs

What does NGINX cache?
• Cache GET and HEAD with no Set-Cookie response
• Uniqueness defined by raw URL or:
proxy_cache_key $scheme$proxy_host$uri$is_args$args;
• Cache time defined by
– X-Accel-Expires
– Cache-Control
– Expires http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html

NGINX Config
proxy_cache_path /tmp/cache keys_zone=one:10m levels=1:2 inactive=60m;
server {
listen 80;
server_name localhost;
location / {
proxy_pass http://localhost:8080;
proxy_cache one;
}
}

Caching is not just for HTTP
• FastCGI
– Functions much like HTTP
• Memcache
– Retrieve content from memcached
server (must be prepopulated)
• uwsgi and SCGI
N
HTTP
FastCGI
memcached
uwsgi
SCGI
NGINX is more than
just a reverse proxy

HOW TO UNDERSTAND WHAT’S GOING ON

Cache Instrumentation
add_header X-Cache-Status $upstream_cache_status;
MISS Response not found in cache; got from upstream. Response may have been
saved to cache
BYPASS proxy_cache_bypass got response from upstream. Response may have
been saved to cache
EXPIRED entry in cache has expired; we return fresh content from upstream
STALE takes control and serves stale content from cache because upstream is not
responding correctly
UPDATING serve state content from cache because cache_lock has timed out and
proxy_use_stale takes control
REVALIDATED proxy_cache_revalidate verified that the current cached content was still
valid (if-modified-since)
HIT we serve valid, fresh content direct from cache

Cache Instrumentation
map $remote_addr $cache_status {
127.0.0.1 $upstream_cache_status;
default “”;
}
server {
location / {
proxy_pass http://localhost:8002;
proxy_cache one;
add_header X-Cache-Status $cache_status;
}
}

Extended Status
Check out: demo.nginx.com
http://demo.nginx.com/status.html http://demo.nginx.com/status

HOW CONTENT CACHING FUNCTIONS
IN NGINX

How it works...
• NGINX uses a persistent disk-based cache
– OS Page Cache keeps content in memory, with hints from
NGINX processes
• We’ll look at:
– How is content stored in the cache?
– How is the cache loaded at startup?
– Pruning the cache over time
– Purging content manually from the cache

How is cached content stored?
proxy_cache_path /tmp/cache keys_zone=one:10m levels=1:2
max_size=40m;
• Define cache key:
proxy_cache_key $scheme$proxy_host$uri$is_args$args;
• Get the content into the cache, then check the md5
$ echo -n "httplocalhost:8002/time.php" | md5sum
6d91b1ec887b7965d6a926cff19379b4 -
• Verify it’s there:
$ cat /tmp/cache/4/9b/6d91b1ec887b7965d6a926cff19379b4

Loading cache from disk
• Cache metadata stored in shared memory segment
• Populated at startup from cache by cache loader
proxy_cache_path path keys_zone=name:size
[loader_files=number] [loader_threshold=time] [loader_sleep=time];
(100) (200ms) (50ms)
– Loads files in blocks of 100
– Takes no longer than 200ms
– Pauses for 50ms, then repeats

Managing the disk cache
• Cache Manager runs periodically, purging files that
were inactive irrespective of cache time, deleteing
files in LRU style if cache is too big
proxy_cache_path path keys_zone=name:size
[inactive=time] [max_size=size];
(10m)
– Remove files that have not been used within 10m
– Remove files if cache size exceeds max_size

Purging content from disk
• Find it and delete it
– Relatively easy if you know the key
• NGINX Plus – cache purge capability
$ curl -X PURGE -D – "http://localhost:8001/*"
HTTP/1.1 204 No Content
Server: nginx/1.5.12
Date: Sat, 03 May 2014 16:33:04 GMT
Connection: keep-alive
X-Cache-Key: httplocalhost:8002/*

Delayed caching
proxy_cache_min_uses number;
• Saves on disk writes for very cool caches
Cache revalidation
proxy_cache_revalidate on;
• Saves on upstream bandwidth and disk writes

Control over cache time
proxy_cache_valid 200 302 10m;
proxy_cache_valid 404 1m;
• Priority is:
– X-Accel-Expires
– Cache-Control
– Expires
– proxy_cache_valid
Set-Cookie response header
means no caching

Cache / don’t cache
proxy_cache_bypass string ...;
proxy_no_cache string ...;
• Bypass the cache – go to origin; may cache result
• No_Cache – if we go to origin, don’t cache result
proxy_no_cache $cookie_nocache $arg_nocache $http_authorization;
• Typically used with a complex cache key, and only if the
origin does not sent appropriate cache-control reponses

Multiple Caches
proxy_cache_path /tmp/cache1 keys_zone=one:10m levels=1:2 inactive=60s;
proxy_cache_path /tmp/cache2 keys_zone=two:2m levels=1:2 inactive=20s;
• Different cache policies for different tenants
• Pin caches to specific disks
• Temp-file considerations – put on same disk!:
proxy_temp_path path [level1 [level2 [level3]]];

Why is page speed important?
• We used to talk about the ‘N second rule’:
– 10-second rule
• (Jakob Nielsen, March 1997)
– 8-second rule
• (Zona Research, June 2001)
– 4-second rule
• (Jupiter Research, June 2006)
– 3-second rule
• (PhocusWright, March 2010)
12
10
8
6
4
2
0
Jan-97
Jan-98
Jan-99
Jan-00
Jan-01
Jan-02
Jan-03
Jan-04
Jan-05
Jan-06
Jan-07
Jan-08
Jan-09
Jan-10
Jan-11
Jan-12
Jan-13
Jan-14

Google changed the rules
“We want you to be able to get
from one page to another as
quickly as you turn the page on
a book”
Urs Hölzle, Google

The costs of poor performance
• Google: search enhancements cost 0.5s page load
– Ad CTR dropped 20%
• Amazon: Artificially increased page load by 100ms
– Customer revenue dropped 1%
• Walmart, Yahoo, Shopzilla, Edmunds, Mozilla…
– All reported similar effects on revenue
• Google Pagerank – Page Speed affects Page Rank
– Time to First Byte is what appears to count

NGINX Caching lets you
Improve end-user performance
Consolidate and simplify your web infrastructure
Increase server capacity
Insulate yourself from server failures

Closing thoughts
• 38% of the world’s busiest websites use NGINX
• Check out the blogs on nginx.com
• Future webinars: nginx.com/webinars
Try NGINX F/OSS (nginx.org) or NGINX Plus (nginx.com)

NGINX High-performance Caching

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