Scenarios start with clients (Tsung cluster) and server definitions:
For non distributed load, you can use a basic setup like:
<clients> <client host="localhost" use_controller_vm="true"/> </clients> <servers> <server host="192.168.1.1" port="80" type="tcp"></server> </servers>
This will start the load on the same host and on the same Erlang virtual machine as the controller.
The server is the entry point into the cluster. You can add several servers, by default each server will have a weight of 1, and each session will choose a server randomly according to the weight. You can set a weight for each server like this (weight can be an integer or a float):
<servers> <server host="server1" port="80" type="tcp" weight="4"></server> <server host="server2" port="80" type="tcp" weight="1"></server> </servers>
(in version older than 1.5.0, the weight option was not implemented and a round robin algorithm was used to choose the server).
Type can be tcp, ssl, udp (for IPv6, use tcp6, ssl6 or udp6 ; only available in version 1.4.2 and newer) or websocket (only available in version 1.5.0 and newer))
The next example is more complex, and use several features for advanced distributed testing:
<clients> <client host="louxor" weight="1" maxusers="800"> <ip value="10.9.195.12"></ip> <ip value="10.9.195.13"></ip> </client> <client host="memphis" weight="3" maxusers="600" cpu="2"/> </clients> <servers> <server host="10.9.195.1" port="8080" type="tcp"></server> </servers>
Several virtual IP can be used to simulate more machines. This is very useful when a load-balancer use the client’s IP to distribute the traffic among a cluster of servers. New in 1.1.1: IP is no longer mandatory. If not specified, the default IP will be used.
New in 1.4.0: You can use <ip scan="yes" value="eth0"/> to scan for all the IP aliases on a given interface (eth0 in this example).
In this example, a second machine is used in the Tsung cluster, with a higher weight, and 2 cpus. Two Erlang virtual machines will be used to take advantage of the number of CPU.
Even if an Erlang VM is now able to handle several CPUs (erlang SMP), benchmarks shows that it’s more efficient to use one VM per CPU (with SMP disabled) for tsung clients. Only the controller node is using SMP erlang. Therefore, cpu should be equal to the number of cores of your nodes. If you prefer to use erlang SMP, add the -s option when starting tsung (and don’t set cpu in the config file).
By default, the load is distributed uniformly on all CPU (one CPU per client by default). The weight parameter (integer) can be used to take into account the speed of the client machine. For instance, if one real client has a weight of 1 and the other client has a weight of 2, the second one will start twice the number of users as the first (the proportions will be 1/3 and 2/3). In the earlier example where for the second client has 2 CPU and weight=3, the weight is equal to 1.5 for each CPU.
The maxusers parameter is used to bypass the limit of maximum number of sockets opened by a single process (1024 by default on many OS) and the lack of scalability of the select system call. When the number of users is higher than the limit, a new erlang virtual machine will be started to handle new users. The default value of maxusers is 800. Nowadays, with kernel polling enable, you can and should use a very large value for maxusers (30000 for example) without performance penalty (but don’t forget to raise the limit of the OS with ulimit -n, see also Why do i have error_connect_emfile errors?).
If you are using a tsung master with slaves, the master distributes sessions to slaves. If a session contains multiples requests, a slave will execute each of these requests in order.
Tsung is able to get its client node list from a batch/job scheduler. It currently handle PBS/torque, LSF and OAR. To do this, set the type attribute to batch, e.g.:
<client type="batch" batch="torque" maxusers="30000">
If you need to scan IP aliases on nodes given by the batch scheduler, use scan_intf like this:
<client type="batch" batch="torque" scan_intf='eth0' maxusers="30000">