Usenix LISA 2012 - Choosing a Proxy

Choosing a Proxy
-
Don’t roll the D20!
Leif Hedstrom
Cisco WebEx

Who am I?
• Unix developer since 1985
• Yeah, I’m really that old, I learned Unix on BSD 2.9
• Long time SunOS/Solaris/Linux user
• Mozilla committer (but not active now)
• VP of Apache Traffic Server PMC
• ASF member
• Overall hacker, geek and technology addict
zwoop@apache.org
@zwoop
+lhedstrom

So which proxy cache should you
choose?

Plenty of Proxy Servers

PerlBal

And plenty of “reliable” sources…

Answer: the one that solves your
problem!

http://mihaelasharkova.files.wordpress.com/2011/05/5steploop2

But first…
• While you are still awake, and the coffee is
fresh:

My crash course in HTTP proxy
and caching!

Why Cache is King
• The content fastest served is the data the user
already has locally on his computer/browser
– This is near zero cost and zero latency!
• The speed of light is still a limiting factor
– Reduce the latency -> faster page loads
• Serving out of cache is computationally cheap
– At least compared to e.g. PHP or any other higher
level page generation system
– It’s easy to scale caches horizontally

Choosing an intermediary

SMP Scalability
and performance

Ease of use HTTP/1.1
Extensible Features

Plenty of Free Proxy Servers

PerlBal

Plenty of Free Caching Proxy
Servers


SMP Scalability
and performance

The problem
• You can basically not buy a computer today
with less than 2 CPUs or cores
• Things will only get “worse”!
– Well, really, it’s getting better
• Typical server deployments today have at least
8 – 16 cores
– How many of those can you actually use??
– And are you using them efficiently??
• NUMA turns out to be kind of a bitch…

Solution 1: Multi-threading
Single CPU Dual CPU

Thread 1 Thread 1 Thread 2

Thread 3
Thread 2
Thread 1

Thread 3
Thread 3
Thread 1

Thread 3

Time Time

Problems with multi-threading
• It’s a wee bit difficult to get it right!

http://www.flickr.com/photos/stuartpilbrow/3345896050

Problems with multi-threading

"When two trains approach each other at a
crossing, both shall come to a full stop
and neither shall start up again until
the other has gone."

From Wikipedia, Illogical statute passed by Kansas legislation .

Solution 2: Event Processing
Scheduled Network Disk I/O
events events events

Queue

Event
Loop

Disk HTTP state Accept
handler machine handler

Can generate new events

Problems with Event Processing
• It hates blocking APIs and
calls!
– Hating it back doesn’t help :/
• Still somewhat complicated
• It doesn’t scale on SMP by
itself

Where are we at ?
Apache TS Nginx Squid Varnish
Processes 1 1 - <n> 1 - <n> 1

Threads Based on cores 1 1 Lots

Evented Yes Yes Yes Yes *)

*) Can use blocking calls, with (large) thread pool

Proxy Cache test setup
• AWS Large instances, 2 CPUs
• All on RCF 1918 network (“internal” net)
• 8GB RAM
• Access logging enabled to disk (except on Varnish)
• Software versions
– Linux v3.2.0
– Traffic Server v3.3.1
– Nginx v1.3.9
– Squid v3.2.5
– Varnish v3.0.3
• Minimal configuration changes
• Cache a real (Drupal) site

ATS configuration
• etc/traffficserver/remap.config:

map / http://10.118.154.58

• etc/trafficserver/records.config:

CONFIG proxy.config.http.server_ports STRING 80

Nginx configuration try 1, basically
defaults (broken, don’t use)
worker_processes 2;
access_log logs/access.log main;

proxy_cache_path /mnt/nginx_cache levels=1:2 keys_zone=my-cache:8m
max_size=16384m inactive=600m;
proxy_temp_path /mnt/nginx_temp;

server {
listen 80;

location / {
proxy_pass http://10.83.145.47/;
proxy_cache my-cache;
}

Nginx configuration try 2 (works but
really slow, 10x slower)
worker_processes 2;


gzip on;
server {
listen 80;

location / {
proxy_set_header Accept-Encoding "";
}

Nginx configuration try 3 (works and
reasonably fast, but WTF!)
worker_processes 2;


server {
listen 80;
set $ae "";
if ($http_accept_encoding ~* gzip) {
set $ae "gzip";
}

location / {
proxy_set_header If-None-Match "";
proxy_set_header If-Modified-Since "";
proxy_set_header Accept-Encoding $ae;
proxy_cache_key $uri$is_args$args$ae;
}

location ~ /purge_it(/.*) {
proxy_cache_purge example.com $1$is_args$args$myae
}

Thanks to Chris Ueland at NetDNA for the snippet

Squid configuration
http_port 80 accel
http_access allow all
cache_mem 4096 MB
workers 2
memory_cache_shared on
cache_dir ufs /mnt/squid 100 16 256
cache_peer 10.83.145.47 parent 80 0 no-query originserver

Varnish configuration
backend default {
.host = "10.83.145.47”;
.port = "80";
}

Performance AWS 8KB HTML (gzip)
10,000 25.0

9,000 22.81

8,000 20.0

Time to first response (ms)
7,000

6,000 15.0
Throughput

5,000 12.16
4,000 10.0
9.20
3,000 7.40 7.92

2,000 5.0

1,000

0 0.0
ATS 3.3.1 Nginx 1.3.9 hack Squid 3.2.5 Varnish 3.0.3 Varnish 3.0.3
varnishlog -w

QPS Latency

10,000 100.00%

9,000 90.00%
82% 83%
8,000 80.00%
73%
7,000 70.00%

CPU used (dual core)
63%
6,000 60% 60.00%
Throughput

5,000 50.00%

4,000 40.00%

3,000 30.00%

2,000 20.00%

1,000 10.00%

0 0.00%
varnishlog -w

QPS CPU usage

Performance AWS 500 bytes JPG
16,000 18.0
16.41 16.0
14,000

14.0
12,000

Time to first response (ms)
12.0
10,000
Throughput

10.0
8,000 9.10
8.0
7.27
6,000
5.93 6.0
4,000 4.95
4.0

2,000 2.0

0 0.0
varnishlog -w

QPS Latency

Performance AWS 500 bytes JPG
16,000 100.00%

90.00%
14,000
84%
78% 80.00%
12,000 77% 77% 76%
70.00%

CPU used (dual core)
10,000
60.00%
Throughput

8,000 50.00%

40.00%
6,000
30.00%
4,000
20.00%
2,000
10.00%

0 0.00%
varnishlog -w

QPS CPU usage


HTTP/1.1
Features

RFC 2616 is not optional!
• Neither is the new BIS revision!
• Understanding HTTP and how it relates to
Proxy and Caching is important
– Or you will get it wrong! I promise.

How things can go wrong: Vary!
$ curl -D - -o /dev/null -s --compress http://10.118.73.168/
HTTP/1.1 200 OK
Server: nginx/1.3.9
Date: Wed, 12 Dec 2012 18:00:48 GMT
Content-Type: text/html; charset=utf-8
Content-Length: 8051
Connection: keep-alive
X-Powered-By: PHP/5.4.9
X-Drupal-Cache: HIT
Etag: "1355334762-0-gzip"
Content-Language: en
X-Generator: Drupal 7 (http://drupal.org)
Cache-Control: public, max-age=900
Last-Modified: Wed, 12 Dec 2012 17:52:42 +0000
Expires: Sun, 19 Nov 1978 05:00:00 GMT
Vary: Cookie,Accept-Encoding
Content-Encoding: gzip

How things can go wrong: Vary!
$ curl -D - -o /dev/null -s http://10.118.73.168/
HTTP/1.1 200 OK
Note: no gzip support
Server: nginx/1.3.9
Date: Wed, 12 Dec 2012 18:00:57 GMT
Content-Type: text/html; charset=utf-8
Content-Length: 8051
Connection: keep-alive
X-Powered-By: PHP/5.4.9
X-Drupal-Cache: HIT
Etag: "1355334762-0-gzip"
Content-Language: en
X-Generator: Drupal 7 (http://drupal.org)
Cache-Control: public, max-age=900
Last-Modified: Wed, 12 Dec 2012 17:52:42 +0000
Expires: Sun, 19 Nov 1978 05:00:00 GMT
Vary: Cookie,Accept-Encoding
Content-Encoding: gzip

EPIC FAIL!

What type of proxy do you need?
• Of our candidates, only two fully supports all
proxy modes!

CoAdvisor HTTP protocol quality tests
for reverse proxies
Varnish 3.0.3
49%

Squid 3.2.5
81%

Nginx 1.3.9
51%

ATS 3.3.1
68%
0 100 200 300 400 500 600

Failures Violations Success

CoAdvisor HTTP protocol quality tests
for reverse proxies
Varnish 3.0.3 25%

Squid 3.2.5 6%

Nginx 1.3.9 27%

ATS 3.3.1 15%

0 100 200 300 400 500 600

Failures Violations Success


Ease of use
Extensible

ATS – The good
• Good HTTP/1.1 support, including SSL
• Tunes itself very well to the system / hardware
at hand
• Excellent cache features and performance
– Raw disk cache is fast and resilient
• Extensible plugin APIs, quite a few plugins
• Used and developed by some of the largest
Web companies in the world

ATS – The bad
• Load balancing is incredibly lame
• Seen as difficult to setup (I obviously disagree)
• Developer community is still too small
• Code is complicated
– By necessity? Maybe …

ATS – The ugly
• Too many configuration files!
• There’s still legacy code that has to be
replaced or removed
• Not a whole lot of commercial support
– But there’s hope (e.g. OmniTI recently announced
packaged support)

Nginx – The good
• Easy to understand the code base, and
software architecture
– Lots of plugins available, including SPDY
• Excellent Web and Application server
– E.g. Nginx + fpm (fcgi) + PHP is the
awesome, according to a very reputable source
• Commercial support available from the people
who wrote and know it best. Huge!

Nginx – The bad
• Adding extensions implies rebuilding the
binary
• By far the most configurations required “out
of the box” to even do anything remotely
useful
• It does not make good attempts to tune itself
to the system
• No good support for conditional requests

Nginx – The ugly
• The cache is a joke! Really
• The protocol support as an HTTP proxy is
rather poor. It fares the worst in the tests, and
can be outright wrong if you are not very
careful
• From docs: “nginx does not handle "Vary"
headers when caching.” Seriously?

Squid – The Good
• Has by far the most HTTP features of the
bunch. I mean, by far, nothing comes even
close
• It also is the best HTTP conformant proxy
today. It has the best scores in the CoAdvisor
tests, by a wide margin
• The features are mature, and used pretty
much everywhere
• Works pretty well out of the box

Squid – The Bad
• Old code base
• Cache is not particularly efficient
• Has traditionally been prone to instability
• Complex configurations
– At least IMO, I hate it

Squid – The Ugly
• SMP is quite an afterthought
– Duct tape
• Why spend so many years rewriting from v2.x to
v3.x without actually addressing some of the real
problems? Feels like a boat has been missed…
• Not very extensible
– Typically you write external “helper”
processes, similar to fcgi. This is not particularly
flexible, nor powerful (can not do everything you’d
want as a helper, so might have to rewrite the Squid
core)

Varnish – The Good
• VCL
• And did I mention VCL? Pure genius!
• Very clever logging mechanism
• ESI is cool, even with its limited subset
– Not unique to Varnish though
• Support from several good commercial
entities

Varnish – The Bad
• Letting the kernel do the hard work might
seem like a good idea on paper, but perhaps
not so great in the real world. But lets not go
into a BSD vs Linux kernel war …
• Persistent caching seems like an after thought
at best
• No good support for conditional requests
• What impact does “real” logging have on
performance?

Varnish – The Ugly
• There are a lot of threads in this puppy!
• No SSL. And presumably, there never will be?
– So what happens with SPDY / HTTP2 ?
• Protocol support is weak, without a massive
amount of VCL.
• And, you probably will need a PhD in VCL!
– There’s a lot of VCL hacking to do to get it to
behave well

Summary
• Please understand your problem`
– Don’t listen to @zwoop on twitter…
• Performance in itself is rarely a key
differentiator; latency, features and
correctness are
• But most important, use a proxy, preferably a
good one, if you run a serious web server

10,000 50.0
9,000 45.87 45.0

Time to firt res p onse (ms)
8,000 40.0
7,000 35.0
Throughput

6,000 30.0
5,000 25.0
22.81
4,000 20.0

s
3,000 15.0
12.16
2,000 9.20 10.0
7.40 7.92
1,000 5.0
0 0.0
ATS 3.3.1 Nginx 1.3.9 Squid 3.2.5 Varnish Varnish Nginx 1.3.9
hack 3.0.3 3.0.3
varnishlog -
w

QPS Latency

If it ain’t broken, don’t fix it
But by all means, make it less sucky!

However, when all you have is a
hammer…

Usenix LISA 2012 - Choosing a Proxy

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