ab的原理：ab命令会创建多个并发访问线程，模拟多个访问者同时对摸一个URL地址进行访问。它的测试目标是基于URL的，因此它既可以用来测试apache的负载压力，也可以测试nginx、lighthttp、tomcat、IIS等其他web服务器的压力。

$ ab -n1000 -c10 http://localhost:3000/

1000条请求，10个并发

相关参数：

-n requests     Number of requests to perform
-c concurrency  Number of multiple requests to make at a time
-t timelimit    Seconds to max. to spend on benchmarkingThis implies -n 50000
-s timeout      Seconds to max. wait for each responseDefault is 30 seconds
-b windowsize   Size of TCP send/receive buffer, in bytes
-B address      Address to bind to when making outgoing connections
-p postfile     File containing data to POST. Remember also to set -T
-u putfile      File containing data to PUT. Remember also to set -T
-T content-type Content-type header to use for POST/PUT data, eg.'application/x-www-form-urlencoded'Default is 'text/plain'
-v verbosity    How much troubleshooting info to print
-w              Print out results in HTML tables
-i              Use HEAD instead of GET
-x attributes   String to insert as table attributes
-y attributes   String to insert as tr attributes
-z attributes   String to insert as td or th attributes
-C attribute    Add cookie, eg. 'Apache=1234'. (repeatable)
-H attribute    Add Arbitrary header line, eg. 'Accept-Encoding: gzip'Inserted after all normal header lines. (repeatable)
-A attribute    Add Basic WWW Authentication, the attributesare a colon separated username and password.
-P attribute    Add Basic Proxy Authentication, the attributesare a colon separated username and password.
-X proxy:port   Proxyserver and port number to use
-V              Print version number and exit
-k              Use HTTP KeepAlive feature
-d              Do not show percentiles served table.
-S              Do not show confidence estimators and warnings.
-q              Do not show progress when doing more than 150 requests
-l              Accept variable document length (use this for dynamic pages)
-g filename     Output collected data to gnuplot format file.
-e filename     Output CSV file with percentages served
-r              Don't exit on socket receive errors.
-m method       Method name
-h              Display usage information (this message)
-Z ciphersuite  Specify SSL/TLS cipher suite (See openssl ciphers)
-f protocol     Specify SSL/TLS protocol