Simon Willison's Weblog: nginx

New tool: an nginx playground

2021-09-24T18:44:12+00:00

Julia Evans built a sandbox tool for interactively trying out an nginx configuration and executing test requests through it. I love this kind of tool, and Julia’s explanation of how they built it using a tiny fly.io instance and a network namespace to reduce the amount of damage any malicious usage could cause is really interesting.

Tags: nginx, security, julia-evans, fly

Weeknotes: Getting my personal Dogsheep up and running again

2021-08-22T04:46:13+00:00

I gave a talk about Dogsheep at Noisebridge's Five Minutes of Fame on Thursday. Just one problem: my regular Dogsheep demo was broken, so I ended up building it from scratch again. In doing so I fixed a few bugs in some Dogsheep tools.

Dogsheep on a Digital Ocean droplet

The latest iteration of my personal Dogsheep runs on a $20/month 4GB/2CPU Digital Ocean Droplet running Ubuntu 20.04 LTS.

It runs a private Datasette instance and a bunch of cron jobs to fetch data from Twitter, GitHub, Foursquare Swarm, Pocket and Hacker News.

It also has copies of my Apple Photos and Apple HealthKit data which I upload manually - plus a copy of my genome for good measure.

Some abbreviated notes on how I set it up, copied from a private GitHub Issues thread:

Create a new Ubuntu droplet, and configure its IP address as the A record for dogsheep.simonwillison.net
Install Python 3 and NGINX and SQLite: apt-get install python3 python3-venv nginx sqlite -y
Use letsencrypt to get an HTTPS certificate for it: apt-get update and then apt install certbot python3-certbot-nginx -y, then certbot --nginx -d dogsheep.simonwillison.net
I had to remove the ipv6only=on; bit from the NGINX configuration due to this bug
Created a dogsheep user, useradd -s /bin/bash -d /home/dogsheep/ -m -G
As that user, created a virtual environment: python3 -mvenv datasette-venv and then datasette-venv/bin/pip install wheel and datasette-venv/bin/pip install datasette datasette-auth-passwords
Created a /etc/systemd/system/datasette.service file with this contents

Created a set of blank SQLite database files in WAL mode in /home/dogsheep using the following:

for f in beta.db twitter.db healthkit.db github.db \
  swarm.db photos.db genome.db simonwillisonblog.db \
  pocket.db hacker-news.db memories.db
do
  sqlite3 $f vacuum
  # And enable WAL mode:
  sqlite3 $f 'PRAGMA journal_mode=WAL;'
done

Started the Datasette service: service datasette start
Configured NGINX to proxy to localhost port 8001, using this configuration

It's a few more steps than I'd like, but the end result was a password-protected Datasette instance running against a bunch of SQLite database files on my new server.

With Datasette up and running, the next step was to start loading in data.

Importing my tweets

I started with Twitter. I dropped my Twitter API access credentials into an auth.json file (as described here) and ran the following:

source /home/dogsheep/datasette-venv/bin/activate
pip install twitter-to-sqlite
twitter-to-sqlite user-timeline /home/dogsheep/twitter.db \
  -a /home/dogsheep/auth.json
@simonw [###############################-----] 26299/29684 00:02:06

That pulled in all 29,684 of my personal tweets.

(Actually, first it broke with an error, exposing a bug that had already been reported. I shipped a fix for that and tried again and it worked.)

Favourited tweets were a little harder - I have 39,904 favourited tweets, but the Twitter API only returns the most recent 3,200. I grabbed those more recent ones with:

twitter-to-sqlite favorites /home/dogsheep/twitter.db \
  -a /home/dogsheep/auth.json

Then I requested my Twitter archive, waited 24 hours and uploaded the resulting like.js file to the server, then ran:

twitter-to-sqlite import twitter.db /tmp/like.js

This gave me an archive_like table with the data from that file - but it wasn't the full tweet representation, just the subset that Twitter expose in the archive export.

The README shows how to inflate those into full tweets:

twitter-to-sqlite statuses-lookup twitter.db \
  --sql='select tweetId from archive_like' \
  --skip-existing
Importing 33,382 tweets [------------------------------------] 0% 00:18:28

Once that was done I wrote additional records into the favorited_by table like so:

sqlite3 twitter.db '
  INSERT OR IGNORE INTO favorited_by (tweet, user)
  SELECT tweetId, 12497 FROM archive_like
'

(12497 is my Twitter user ID.)

I also came up with a SQL view that lets me see just media attached to tweets:

sqlite-utils create-view twitter.db media_details "
select
  json_object('img_src', media_url_https, 'width', 400) as img,
  tweets.full_text,
  tweets.created_at,
  tweets.id as tweet_id,
  users.screen_name,
  'https://twitter.com/' || users.screen_name || '/status/' || tweets.id as tweet_url
from
  media
  join media_tweets on media.id = media_tweets.media_id
  join tweets on media_tweets.tweets_id = tweets.id
  join users on tweets.user = users.id
order by
  tweets.id desc
"

Now I can visit /twitter/media_details?_where=tweet_id+in+(select+tweet+from+favorited_by+where+user+=+12497) to see the most recent media tweets that I've favourited!

Swarm checkins

Swarm checkins were a lot easier. I needed my previously-created Foursquare API token, and swarm-to-sqlite:

pip install swarm-to-sqlite
swarm-to-sqlite /home/dogsheep/swarm.db --token=...

This gave me a full table of my Swarm checkins, which I can visualize using datasette-cluster-map:

Apple HealthKit

I don't yet have full automation for my Apple HealthKit data (collected by my Apple Watch) or my Apple Photos - both require me to run scripts on my laptop to create the SQLite database file and then copy the result to the server via scp.

healthkit-to-sqlite runs against the export.zip that is produced by the Apple Health app on the iPhone's export data button - for me that was a 158MB zip file which I AirDropped to my laptop and converted (after fixing a new bug) like so:

healthkit-to-sqlite ~/Downloads/export.zip healthkit.db
Importing from HealthKit  [-----------------------------]    2%  00:02:25

I uploaded the resulting 1.5GB healthkit.db file and now I can do things like visualize my 2017 San Francisco Half Marathon run on a map:

Apple Photos

For my photos I use dogsheep-photos, which I described last year in Using SQL to find my best photo of a pelican according to Apple Photos. The short version: I run this script on my laptop:

# Upload original photos to my S3 bucket
dogsheep-photos upload photos.db \
  ~/Pictures/Photos\ Library.photoslibrary/originals
dogsheep-photos apple-photos photos.db \
  --image-url-prefix "https://photos.simonwillison.net/i/" \
  --image-url-suffix "?w=600"
scp photos.db dogsheep:/home/dogsheep/photos.db

photos.db is only 171MB - it contains the metadata, including the machine learning labels, but not the photos themselves.

And now I can run queries for things like photos of food I've taken in 2021:

Automation via cron

I'm still working through the last step, which involves setting up cron tasks to refresh my data periodically from various sources. My crontab currently looks like this:

# Twitter
1,11,21,31,41,51 * * * * /home/dogsheep/datasette-venv/bin/twitter-to-sqlite user-timeline /home/dogsheep/twitter.db -a /home/dogsheep/auth.json --since
4,14,24,34,44,54 * * * * run-one /home/dogsheep/datasette-venv/bin/twitter-to-sqlite mentions-timeline /home/dogsheep/twitter.db -a /home/dogsheep/auth.json --since
11 * * * * run-one /home/dogsheep/datasette-venv/bin/twitter-to-sqlite user-timeline /home/dogsheep/twitter.db cleopaws -a /home/dogsheep/auth.json --since
6,16,26,36,46,56 * * * * run-one /home/dogsheep/datasette-venv/bin/twitter-to-sqlite favorites /home/dogsheep/twitter.db -a /home/dogsheep/auth.json --stop_after=50

# Swarm
25 */2 * * * /home/dogsheep/datasette-venv/bin/swarm-to-sqlite /home/dogsheep/swarm.db --token=... --since=2w

# Hacker News data every six hours
35 0,6,12,18 * * * /home/dogsheep/datasette-venv/bin/hacker-news-to-sqlite user /home/dogsheep/hacker-news.db simonw

# Re-build dogsheep-beta search index once an hour
32 * * * * /home/dogsheep/datasette-venv/bin/dogsheep-beta index /home/dogsheep/beta.db /home/dogsheep/dogsheep-beta.yml

I'll be expanding this out as I configure more of the Dogsheep tools for my personal instance.

TIL this week

Releases this week

healthkit-to-sqlite: 1.0.1 - (9 releases total) - 2021-08-20
Convert an Apple Healthkit export zip to a SQLite database
twitter-to-sqlite: 0.21.4 - (27 releases total) - 2021-08-20
Save data from Twitter to a SQLite database
datasette-block-robots: 1.0 - (5 releases total) - 2021-08-19
Datasette plugin that blocks robots and crawlers using robots.txt
sqlite-utils: 3.16 - (85 releases total) - 2021-08-18
Python CLI utility and library for manipulating SQLite databases
datasette-debug-asgi: 1.1 - (3 releases total) - 2021-08-17
Datasette plugin for dumping out the ASGI scope

Tags: linux, nginx, datasette, dogsheep, weeknotes

Client-Side Certificate Authentication with nginx

2019-10-05T17:26:35+00:00

Client-Side Certificate Authentication with nginx

I’m intrigued by client-side browser certificates, which allow you to lock down a website such that only browsers with a specific certificate installed can access them. They work on both laptops and mobile phones. I followed the steps in this tutorial and managed to get an nginx instance running which only allows connections from my personal laptop and iPhone.

Tags: certificates, nginx, security, dogsheep

NGINX: Authentication Based on Subrequest Result

2019-10-04T15:36:33+00:00

NGINX: Authentication Based on Subrequest Result

TIL about this neat feature of NGINX: you can use the auth_request directive to cause NGINX to make an HTTP subrequest to a separate authentication server for each incoming HTTP request. The authentication server can see the cookies on the incoming request and tell NGINX if it should fulfill the parent request (via a 2xx status code) or if it should be denied (by returning a 401 or 403). This means you can run NGINX as an authenticating proxy in front of any HTTP application and roll your own custom authentication code as a simple webhook-recieving endpoint.

Via Ishan Anand

Tags: authentication, nginx, webhooks

Mozilla Telemetry: In-depth Data Pipeline

2018-04-12T15:44:42+00:00

Mozilla Telemetry: In-depth Data Pipeline

Detailed behind-the-scenes look at an extremely sophisticated big data telemetry processing system built using open source tools. Some of this is unsurprising (S3 for storage, Spark and Kafka for streams) but the details are fascinating. They use a custom nginx module for the ingestion endpoint and have a “tee” server written in Lua and OpenResty which lets them route some traffic to alternative backend.

Via @reid_write

Tags: analytics, lua, mozilla, nginx, big-data, kafka

Andrew Godwin's www-router Docker container

2018-02-21T05:04:02+00:00

Andrew Godwin's www-router Docker container

Really clever Docker trick: a container that runs Nginx and uses it to route traffic to other containers based on the hostname—but the hostnames to be routed are configured using environment variables which the run-nginx.py CMD script uses to dynamically construct an nginx config when the container starts.

Via @andrewgodwin on Twitter

Tags: andrew-godwin, nginx, docker

nginx proxy-cache-lock

2017-11-14T21:53:07+00:00

nginx proxy-cache-lock

Crucially important feature hidden away in the nginx documentation: proxy_cache_lock enables request coalescing, or dog-pile protection: it means that if a hundred simultaneous requests all suffer the same cache miss, only one request is made to the backend and the answer is then sent back to all hundred requests at once. I’ve leaned heavily on this feature in Varnish for years—useful to know that nginx has the same capability.

Via How Discord Resizes 150 Million Images Every Day with Go and C++

Tags: caching, dogpile, nginx, varnish

Running gunicorn behind nginx on Heroku for buffering and logging

2017-10-02T01:57:20+00:00

Heroku's default setup for Django uses the gunicorn application server. Each Heroku dyno can only run a limited number of gunicorn workers, which means a limited number of requests can be served in parallel (around 4 per dyno is a good rule of thumb).

Where things get nasty is when you have devices on slow connections - like mobile phones. Heroku's router buffers headers but it does not buffer response bodies, so a slow device could hold up a gunicorn worker for several seconds. Too many slow devices at once and the site will become unavailable to other users.

This issue is explained and discussed here: Don't use Gunicorn to host your Django sites on Heroku

That article recommends using waitress as an alternative to gunicorn, but in the comments at the bottom of the article people suggest using a Heroku nginx-buildpack as an alternative.

Here is a slightly out-of-date tutorial on getting this all set up: https://koed00.github.io/Heroku_setups/

I used the following commands to set up the buildpacks:

heroku stack:set cedar-14
heroku buildpacks:clear
heroku buildpacks:add https://github.com/beanieboi/nginx-buildpack.git
heroku buildpacks:add https://github.com/heroku/heroku-buildpack-python.git

Unfortunately the nginx buildpack is not yet compatible with the new heroku-16 stack, so until the nginx buildpack has been updated it's necessary to run the application on the older cedar-14 stack. See this discussion for details: ryandotsmith/nginx-buildpack#68

Adding nginx in this way also gives us the opportunity to fix another limitation of Heroku: its default logging configuration. By default, log lines produced by Heroku (visible using heroku logs --tail or with a logging addon such as Papertrail) look like this:

    Oct 01 18:01:06 simonwillisonblog heroku/router: at=info
        method=GET path="/2017/Oct/1/ship/" host=simonwillison.net
        request_id=bb22f67e-6924-4e81-b6ad-74d1f465cda7
        fwd="2001:8003:74c5:8b00:79e4:80ed:fa85:7b37,108.162.249.198"
        dyno=web.1 connect=0ms service=338ms status=200 bytes=4523 protocol=http

Notably missing here is both the user-agent string and the referrer header sent by the browser! If you're a fan of tailing log files these omissions are pretty disappointing.

The nginx buildback I'm using loads a default configuration file at config/nginx.conf.erb. By including my own copy of this file I can override the original and define my own custom log format.

Having applied this change, the new log lines look like this:

    2017-10-02T01:44:38.762845+00:00 app[web.1]:
        measure#nginx.service=0.133 request="GET / HTTP/1.1" status_code=200
        request_id=8b6402de-d072-42c4-9854-0f71697b30e5 remote_addr="10.16.227.159"
        forwarded_for="199.188.193.220" forwarded_proto="http" via="1.1 vegur"
        body_bytes_sent=12666 referer="-" user_agent="Mozilla/5.0 (Macintosh;
        Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko)
        Chrome/61.0.3163.100 Safari/537.36"

This blog entry started life as a commit message.

Tags: django, logging, nginx, user-agents, heroku, gunicorn

What exactly the error meaning client closed prematurely connection while sending to client from upstream in nginx?

2013-10-27T13:33:00+00:00

My answer to What exactly the error meaning client closed prematurely connection while sending to client from upstream in nginx? on Quora

I think it means that the connection to the user's browser was lost before the request had been fully transferred - for example due to the user hitting the stop button in their browser or switching off their wifi connection.

Tags: nginx, quora

How can I determine which web server a particular website is using (Apache, IIS, Nginx, etc)?

2011-01-05T13:37:00+00:00

My answer to How can I determine which web server a particular website is using (Apache, IIS, Nginx, etc)? on Quora

If you're on Linux or OS X, use curl with the -I option (to make a HEAD request and see the HTTP headers):

$ curl -I www.op3intl.com
HTTP/1.1 200 OK
Date: Thu, 06 Jan 2011 03:31:28 GMT
Server: Microsoft-IIS/6.0

...

Tags: apache, iis, nginx, servers, web-development, webservers, quora

What are the advantages of running Apache behind nginx as opposed to just Apache by itself?

2010-10-12T14:09:00+00:00

My answer to What are the advantages of running Apache behind nginx as opposed to just Apache by itself? on Quora

I do this for all of my Django stuff - I have Django running on modwsgi on a stripped down Apache (almost no configuration except for the modwsgi stuff), then I put an nginx on port 80 which serves the static files directly and proxies dynamic requests back to Apache.

There are a few advantages to this. Firstly, I use non-threaded Apache so each Apache worker process tends to be pretty big (having a full Python interpreter + Django application running in it). It's a horrible waste of resources for one of those fat processes to sit around serving up a static file instead of serving a dynamic request. Secondly, nginx deals with slow connections for me - if someone on a modem (or 3G phone) hits my site I don't tie up an Apache process for several seconds to respond to their request. Instead, nginx sucks the response in from Apache in a few ms and then spools it out to the slow client at whatever rate they can handle. Since nginx is evented it can handle hundreds or even thousands of slow clients at once using very little memory.

Finally, if I'm running an nginx proxy at the "front" of my stack it's trivial for me to start load balancing to more than one Apache servers if I need to.

Tags: apache, nginx, webservers, quora

Multi-node: Concurrent NodeJS HTTP Server

2010-07-15T08:22:00+00:00

Multi-node: Concurrent NodeJS HTTP Server

Kris Zyp’s library for spawning multiple Node child processes (one per core is suggested) for concurrent request handling, taking advantage of Node’s child_process module. This alleviates the need to run multiple Node instances behind an nginx load balancer in order to take advantage of multiple cores.

Tags: javascript, kriszyp, nginx, nodejs, recovered

Introduction to nginx.conf scripting

2010-04-21T23:40:46+00:00

Introduction to nginx.conf scripting

Slideshow—hit left arrow to navigate through the slides. The nginx community is officially nuts. Starts out with a simple “Hello world” using the echo module, then rapidly descends down the rabbit hole in to array operations, sub-requests, memcached connection pooling and eventually non-blocking Drizzle SQL execution against a sharded cluster—all implemented in the nginx.conf configuration file.

Tags: drizzle, http, memcached, nginx

jacobian's django-deployment-workshop

2010-02-19T14:28:35+00:00

jacobian's django-deployment-workshop

Notes and resources from Jacob’s 3 hour Django deployment workshop at PyCon, including example configuration files for Apache2 + mod_wsgi, nginx, PostgreSQL and pgpool.

Tags: apache, deployment, django, jacob-kaplan-moss, modwsgi, nginx, pgpool, postgresql, pycon, python, sysadmin

Round-robin Django setup with nginx

2009-12-21T15:43:42+00:00

Round-robin Django setup with nginx

An nginx trick I didn’t know: a low proxy_connect_timeout value (e.g. 2 seconds) combined with the proxy_next_upstream setting means that if one of your backends breaks a user won’t even see an error, they’ll just have a short delay before getting a response from a working server.

Tags: django, load-balancing, nginx, ops, sysadmin

Simple CouchDB multi-master clustering via Nginx

2009-11-19T16:37:36+00:00

Simple CouchDB multi-master clustering via Nginx

An impressive combination. CouchDB can be easily set up in a multi-master configuration, where writes to one master are replicated to the other and vice versa. This makes setting up a reliable CouchDB cluster is as simple as putting two such servers behind a single nginx proxy.

Tags: cluster, couchdb, load-balancing, multimaster, nginx, replication

How We Made GitHub Fast

2009-10-21T21:14:38+00:00

How We Made GitHub Fast

Detailed overview of the new GitHub architecture. It’s a lot more complicated than I would have expected—lots of moving parts are involved in ensuring they can scale horizontally when they need to. Interesting components include nginx, Unicorn, Rails, DRBD, HAProxy, Redis, Erlang, memcached, SSH, git and a bunch of interesting new open source projects produced by the GitHub team such as BERT/Ernie and ProxyMachine.

Tags: drbd, erlang, ernie, git, github, haproxy, memcached, nginx, proxymachine, rails, redis, replication, ruby, scaling, ssh, unicorn

nginx_http_push_module

2009-10-17T16:48:31+00:00

nginx_http_push_module

More clever design with webhooks—here’s an nginx module that provides a comet endpoint URL which will hang until a back end process POSTs to another URL on the same server. This makes it much easier to build asynchronous comet apps using regular synchronous web frameworks such as Django, PHP and Rails.

Tags: comet, django, nginx, php, rails, webhooks

Ravelry

2009-09-03T18:50:20+00:00

Ravelry

Tim Bray interviews Casey Forbes, the single engineer behind Ravelry, the knitting community that serves 10 million Rails requests a day using just seven physical servers, MySQL, Sphinx, memcached, nginx, haproxy, passenger and Tokyo Cabinet.

Tags: caseyforbes, haproxy, memcached, mysql, nginx, passenger, rails, ravelry, scaling, sphinx-search, tim-bray, tokyocabinet, tokyotyrant

Phusion Passenger for nginx

2009-04-20T04:53:55+00:00

Phusion Passenger for nginx

Passenger (aka mod_rails / mod_rack) enables easy deployment of Rails and Ruby apps under Apache... and the latest version adds support for nginx as well. It works as an HTTP proxy and process manager, spawning worker processes and forwarding HTTP requests to them via a request queue. It can also handle Python WSGI applications—anyone tried it out for that yet?

Tags: apache, deployment, nginx, passenger, python, rails, ruby

Paul Buchheit: Make your site faster and cheaper to operate in one easy step

2009-04-17T17:19:44+00:00

Paul Buchheit: Make your site faster and cheaper to operate in one easy step

Paul promotes gzip encoding using nginx as a proxy, and mentions that FriendFeed use a “custom, epoll-based python server” as their application server. Does that mean that they’re serving their real-time comet feeds directly from Python?

Tags: comet, epoll, friendfeed, gzip, nginx, paul-buchheit, python

How to use Django with Apache and mod_wsgi

2009-04-01T00:24:04+00:00

How to use Django with Apache and mod_wsgi

My favourite deployment option is now included in the official Django docs, thanks to Alex Gaynor. I tend to run a stripped down Apache with mod_wsgi behind an nginx proxy, and have nginx serve static files directly. This avoids the need for a completely separate media server (although a separate media domain is still a good idea for better client-side performance).

Tags: alex-gaynor, deployment, django, modwsgi, nginx, proxies, python, wsgi

Future roadmap for mod_wsgi

2009-03-19T17:27:01+00:00

Future roadmap for mod_wsgi

mod_wsgi 3.0 isn’t too far off, and will include Python 3.0 support, WSGI application preloading and internal web server redirection (similar to nginx X-Accel-Redirect). Version 4.0 plans a major architectural change that will allow multiple versions of Python to be run from the same Apache.

Tags: apache, graham-dumpleton, modwsgi, nginx, python, wsgi

The Django and Ubuntu Intrepid Almanac

2009-02-14T15:42:58+00:00

The Django and Ubuntu Intrepid Almanac

Will Larson’s impressively comprehensive guide to configuring and securing an Ubuntu VPS from scratch to run Django, using PostgreSQL and Apache/mod_wsgi behind nginx.

Tags: apache, django, modwsgi, nginx, postgresql, sysadmin, ubuntu, vps, will-larson

Minimal nginx conf to split get/post requests

2008-10-14T16:33:38+00:00

Minimal nginx conf to split get/post requests

Interesting idea for master-slave replication balancing where GET v.s. POST is load-balanced by nginx, presumably to different backend servers that are configured to talk to either a slave or a master. This won’t deal very will with replication lag though—you really want a user’s session to be bound to the master server for the next few GET requests after data is modified to ensure they see the effects of their updates. UPDATE: Amit fixed my complaint with a neat hack based around a cookie with a max age of 10 seconds.

Tags: load-balancing, masterslave, mysql, nginx, replication

ncache

2008-06-18T20:09:48+00:00

ncache

A squid-style caching system built on top of nginx. Supports the HTTP PURGE method for cache invalidation.

Tags: cache, http, ncache, nginx, purge, squid

Load Balancer Update

2008-05-01T10:06:13+00:00

Load Balancer Update

WordPress.com has switched from Pound to nginx for load balancing, resulting in a significant drop in CPU usage. I’ve been using nginx on my little VPS for over a year now with no complaints, nice to know it scales up as well as down.

Tags: load-balancing, nginx, pound, wordpress, wordpresscom

Nginx and Memcached, a 400% boost!

2008-02-11T22:05:11+00:00

Nginx and Memcached, a 400% boost!

Ilya Grigorik wrote up my current favourite nginx trick—you set nginx to check memcached for a cache entry matching the current URL on every hit, then invalidate your cache by pushing a new cache record straight in to memcached from your application server.

Tags: caching, ilyagrigorik, memcached, nginx, performance

NginxMemcachedModule

2007-12-15T01:59:23+00:00

NginxMemcachedModule

nginx can be set up to directly serve a URL from memcache if the corresponding cache key is set, and fall back to a backend application server otherwise. Application servers can then write directly to memcache when content needs to be cached or goes stale.

Tags: caching, memcache, memcached, nginx, scaling

A Fair Proxy Balancer for Nginx and Mongrel

2007-12-09T14:57:44+00:00

A Fair Proxy Balancer for Nginx and Mongrel

nginx uses round robin for proxying by default; this extension module ensures requests are queued up and sent through to backend mongrel servers that aren’t currently busy. I don’t see any reason this wouldn’t work with servers other than mongrel.

Tags: fair, load-balancing, mongrel, nginx, proxies