Name:
    tcpcopy
    It is an online request replication tool and is mainly for testing tasks using netlink and raw sockets


Description:
    It can help you find bugs in your online project without actually being online. 
    And it can also be used to test the stress that a system could endure.

    For example, if your system already has "memcached" subsystem and you want to 
    use "membase" to replace it, tcpcopy can assist you to test "membase". While your 
    old memcached system is still running online, tcpcopy could copy the flow of packets 
    from memcached to membase. From the point view of membase, the flow is accessing 
    membase(just like membase online), and it will not affect memcached at all except 
    network bandwidth and a little cpu load.


Functionalities:
    1) Distributed Stress Test
        You can use online data to test the stress that your target machine can endure. It is better 
        than apache ab tool and you can find bugs that only occur during high-stress situations.
    2) Hot Backup
        It is very suitable for backup tasks if connections are short-lived and the request loss rate
        is very low(1/100000).
    3) Normal Online Test
        You can find whether the new system is stable and find bugs that only occur in actual 
        online environments.
    4) Comparison Test
        For example, you can use tcpcopy to compare the performances of apache and nginx.


Characteristics:
    1)real time
    2)realistic
    3)efficient
    4)easy to use
    5)distributed
    6)significant


How to use tcpcopy?
    preparing steps:
      1) download souce code
      2)./configure
      3)make
      4)make install

    running steps:
      the target machine(root privilege):
          modprobe ip_queue (if not running)
          iptables -I OUTPUT -p tcp --sport port -j QUEUE (if not set)
          ./interception 
      online machine(root privilege):
          ./tcpcopy local_ip1[:local_ip2:...] local_port  remote_ip  remote_port 
 

An example:
    Suppose 13 and 14 are online machines, 148 is a target machine which is similar to 
    the online machines, and 12321 is used both as local port and remote port. We 
    use tcpcopy to test if 148 can endure two times of current online stress.
    
    Using tcpcopy to perform the above test task.
    the target machine(148)
       # modprobe ip_queue (if not run up)
       # iptables -I OUTPUT -p tcp --sport 12321 -j QUEUE (if not set)
       # ./interception
    online machine(13):
       # ./tcpcopy xx.xx.xx.13 12321 xx.xx.xx.148 12321
    online machine(14):
       # ./tcpcopy xx.xx.xx.14 12321 xx.xx.xx.148 12321

    Cpu load and memory usage are as follows:
        13 cpu:
           11124 adrun 15 0 193m 146m 744 S 18.6 7.3 495:31.56 asyn_server
           11281 root 15 0 65144 40m 1076 S 12.3 2.0 0:47.89 tcpcopy
        14 cpu:
           16855 adrun 15 0 98.7m 55m 744 S 21.6 2.7 487:49.51 asyn_server
           16429 root 15 0 41156 17m 1076 S 14.0 0.9 0:33.63 tcpcopy
        148 cpu :
           25609 root 15 0 76892 59m 764 S 49.6 2.9 63:03.14 asyn_server
           20184 root 15 0 5624 4232 292 S 17.0 0.2 0:52.82 interception

    Access log analysis:
        13 online machine: grep 'Tue 11:08' access_0913_11.log |wc -l :89316,  1489 reqs/sec
        14 online machine: grep 'Tue 11:08' access_0913_11.log |wc -l :89309,  1488 reqs/sec
        148 test  machine: grep 'Tue 11:08' access_0913_11.log |wc -l :178175, 2969 reqs/sec
        request loss rate:
           (89316+89309-178175)/(89316+89309)=0.25%

    From the above, we can see that the target machine can endure two times of current 
    online stress.
    
    What about the cpu load ?
    tcpcopy on online machine 13 occupies 12.3% of cpu load, tcpcopy on online 14 
    occupies 14% and interception on target machine 148 occupies 17%. We can see 
    that the cpu load is very low here, and so is the memory usage.


Attention:
    1) It is tested on machines running linux (kernal 2.6 or above).
    2) tcpcopy is similar to udp, so sometimes it may lose requests.
    3) If you tcpcopy local request, please set lo MTU not more than 1500.
    4) Interception(tcpcopy server) is single threaded.
    5) tcpcopy needs root privilege.
    6) long request(such as uploading a large file) is not working well here(no retransmission when sending packets to the target test server)
    7) Check error.log if you have trouble and email to me(163.beijing@gmail.com or wangbin579@gmail.com).