Website load testing with Apache Bench
For basic website load testing Apache Bench is a fantastic tool that is easy to use and can be integrated into your build/deployment processes. It is not limited to testing Apache webservers and can be used with any website.
To demonstrate Apache Bench (AB) I'm using two AWS EC2 instances, one with an out of the box install of Wordpress running on Apache and the other running Apache Bench.
I would highly recommend using a separate server to run AB.
Start by installing Apache Bench (AB):
apt-get install apache2-utils
or
yum install httpd-tools
Apace Bench (AB) usage:
ab [options] [http[s]://]hostname[:port]/path
More often that not you will use the following switches:
ab -n [number of requests to perform] -c [number of multiple requests to make] [http[s]://]hostname[:port]/path
You can include cookies, basic authentication, headers and more.
Let's get testing:
A very simple test, a single request:
ab -n 1 -c 1 http://10.75.33.123:80/
Output:
Server Software: Apache/2.2.22
Server Hostname: 10.75.33.123
Server Port: 80
Document Path: /
Document Length: 7412 bytes
Concurrency Level: 1
Time taken for tests: 0.281 seconds
Complete requests: 1
Failed requests: 0
Write errors: 0
Total transferred: 7681 bytes
HTML transferred: 7412 bytes
Requests per second: 3.56 [#/sec] (mean)
Time per request: 281.030 [ms] (mean)
Time per request: 281.030 [ms] (mean, across all concurrent requests)
Transfer rate: 26.69 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 0 0.0 0 0
Processing: 281 281 0.0 281 281
Waiting: 280 280 0.0 280 280
Total: 281 281 0.0 281 281
You can see very quickly from the output that the request took 0.281 seconds to complete.
A test levering more load, 500 requests with a concurrency level of 50:
ab -n 500 -c 50 http://10.75.33.123:80/
Output:
Concurrency Level: 50
Time taken for tests: 145.788 seconds
Complete requests: 500
Failed requests: 0
Write errors: 0
Total transferred: 3840500 bytes
HTML transferred: 3706000 bytes
Requests per second: 3.43 [#/sec] (mean)
Time per request: 14578.770 [ms] (mean)
Time per request: 291.575 [ms] (mean, across all concurrent requests)
Transfer rate: 25.73 [Kbytes/sec] received
Connection Times (ms)
min mean[+/-sd] median max
Connect: 0 1 1.8 0 12
Processing: 2519 14355 3368.7 14024 27403
Waiting: 2519 14348 3361.0 14023 27403
Total: 2520 14355 3368.6 14030 27404
Let's pick out some key lines in the output:
Time taken for tests: 145.788 seconds
The total time taken for the tests to complete.
Number of failed requests: 0
If you see any errors here it may indicate that the website you are testing is straining under the load of the test, either reduce the concurrency or number of requests.
Requests per second: 3.43 [#/sec] (mean)
The number of requests handled by the website per second, on average.
Time per request: 291.575 [ms] (mean, across all concurrent requests)
The average time per request handled by the website.
Time per request: 14578.770 [ms] (mean)
This is the average time per request factoring in concurrency (i.e. 291.575 * 50)
Connect Times (ms)
min mean[+/-sd] median max
Total: 2520 14355 3368.6 14030 27404
Min: The shortest request time during the test, 2,520ms (2.52s)
Mean[+/-sd]: The average request time during the test plus the standard deviation, 14,355ms (14.355s) with a deviation of +/- 3,368.6 (3.3686s)
Median: The 'middle' request time during the test, 14,030ms (14s)
Max: The longest request time during the test, 27,404ms (27.4s)
I guess with an average request time of ~14 seconds I should look into adding some layers of cache and optimising the Wordpress install :)
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