27 Jan 2013

600k concurrent HTTP connections, with Clojure & http-kit

Inspired by Scaling node.js to 100k concurrent connections! and Node.js w/250k concurrent connections!. I did some test for http-kit!

http-kit manages to make 600k concurrent connections, on PC!

Server’s logic

The server read the length param from the request, generate a string of that length.

;; main.clj
;; ~20k string
(def const-str (apply str (repeat 200 "http-kit is a http server & client written from scrach for high performance clojure web applications, support async and websocket")))

(defn handler [req]
  (let [length (to-int (or (-> req :params :length) 1024))]
    {:status 200
     :headers {"Content-Type" "text/plain"}
     :body (subs const-str 0 (max (min 10240 length) 1))}))

(defn -main [& args]
  (run-server (-> handler wrap-keyword-params wrap-params)
              {:port 8000})
  (println (str "Server started. listen at")))

Start the server:

java -server -Xms3072m -Xmx3072m -cp `lein classpath` clojure.main -m main

Linux config

The server need to set max allowed open file to a much larger value. The default value is ~1024

echo 9999999 | sudo tee /proc/sys/fs/nr_open
echo 9999999 | sudo tee /proc/sys/fs/file-max

# edit /etc/security/limits.conf, add the following line, need logout and login again
* - nofile 4999999

# set before run the server and test code
ulimit -n 4999999

More ports for test code to use

sudo sysctl -w net.ipv4.ip_local_port_range="1025 65535"

Hardware & Software

The server and test code are both run on my desktop:

How to make 600k concurrent connections on a single PC

A IP can only issue most 65536 connections to a server, since socket port is unsigned short. But we can bypass this limit. On Linux, it’s quite easy to set up virtual network interface:

for i in `seq 200 230`; do sudo ifconfig eth0:$i 192.168.1.$i up ; done

Then your computer have many IPs, from to The server bind to, the client can connect, or, etc. Per IP can have about 60K concurrent connections. Then the client can issue as many concurrent connections as it needed.

Concurrency test code

The client opens 600k concurrent keep-alived connections to the server, request the server to return string of length randomly between 1 ~ 4096 bytes, read the response, idle 5s ~ 45s (randomly pick a value between), request again.


time 0s, concurrency: 100, total requests: 0, thoughput: 0.00M/s, 0.00 requests/seconds
time 40s, concurrency: 164000, total requests: 230142, thoughput: 11.78M/s, 5688.28 requests/seconds
time 89s, concurrency: 340100, total requests: 788985, thoughput: 18.23M/s, 8812.23 requests/seconds
time 179s, concurrency: 595166, total requests: 2483174, thoughput: 28.61M/s, 13837.77 requests/seconds
time 180s, concurrency: 597853, total requests: 2506378, thoughput: 28.71M/s, 13888.67 requests/seconds
time 183s, concurrency: 600000, total requests: 2529020, thoughput: 28.52M/s, 13788.14 requests/seconds
time 185s, concurrency: 600000, total requests: 2537212, thoughput: 28.20M/s, 13680.42 requests/seconds
time 930s, concurrency: 600000, total requests: 17457773, thoughput: 38.64M/s, 18763.53 requests/seconds
time 931s, concurrency: 600000, total requests: 17477678, thoughput: 38.69M/s, 18764.73 requests/seconds

How about ab test when 600k connections are kept

Issue this command from command line:

ab -n 100000 -c 10 -k

output: ab output

Server Software:        http-kit
Server Hostname:
Server Port:            8000

Document Path:          /
Document Length:        1024 bytes

Concurrency Level:      10
Time taken for tests:   3.184 seconds
Complete requests:      100000
Failed requests:        0
Write errors:           0
Keep-Alive requests:    100000
Total transferred:      117000000 bytes
HTML transferred:       102400000 bytes
Requests per second:    31405.53 [#/sec] (mean)
Time per request:       0.318 [ms] (mean)
Time per request:       0.032 [ms] (mean, across all concurrent requests)
Transfer rate:          35883.27 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.0      0       0
Processing:     0    0   9.3      0     913
Waiting:        0    0   9.3      0     913
Total:          0    0   9.3      0     913

Percentage of the requests served within a certain time (ms)
  50%      0
  66%      0
  75%      0
  80%      0
  90%      0
  95%      0
  98%      0
  99%      0
 100%    913 (longest request)

The Clojure Server’s CPU usage

jvisualvm’s snapshot file.

cpu usage

The Clojure Server’s heap usage

heap memory usage

Run it yourself

The complete test code is available on github. Checkout and run it yourself!

To report a bug, or general discussion: https://github.com/http-kit/scale-clojure-web-app/issues

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