Running Locust distributed¶

Once a single machine isn’t enough to simulate the number of users that you need, Locust supports running load tests distributed across multiple machines.

To do this, you start one instance of Locust in master mode using the --master flag. This is the instance that will be running Locust’s web interface where you start the test and see live statistics. The master node doesn’t simulate any users itself. Instead you have to start one or —most likely—multiple slave Locust nodes using the --slave flag, together with the --master-host (to specify the IP/hostname of the master node).

A common set up is to run a single master on one machine, and then run one slave instance per processor core on the slave machines.

Note

Both the master and each slave machine, must have a copy of the locust test scripts when running Locust distributed.

Note

It’s recommended that you start a number of simulated users that are greater than number of locust classes * number of slaves when running Locust distributed.

Otherwise - due to the current implementation - you might end up with a distribution of the Locust classes that doesn’t correspond to the Locust classes’ weight attribute. And if the hatch rate is lower than the number of slave nodes, the hatching would occur in “bursts” where all slave node would hatch a single user and then sleep for multiple seconds, hatch another user, sleep and repeat.

Example¶

To start locust in master mode:

locust -f my_locustfile.py --master

And then on each slave (replace 192.168.0.14 with IP of the master machine):

locust -f my_locustfile.py --slave --master-host=192.168.0.14

Options¶

`--master`¶

Sets locust in master mode. The web interface will run on this node.

`--slave`¶

Sets locust in slave mode.

`--master-host=X.X.X.X`¶

Optionally used together with --slave to set the hostname/IP of the master node (defaults to 127.0.0.1)

`--master-port=5557`¶

Optionally used together with --slave to set the port number of the master node (defaults to 5557).

`--master-bind-host=X.X.X.X`¶

Optionally used together with --master. Determines what network interface that the master node will bind to. Defaults to * (all available interfaces).

`--master-bind-port=5557`¶

Optionally used together with --master. Determines what network ports that the master node will listen to. Defaults to 5557.

`--expect-slaves=X`¶

Used when starting the master node with --no-web. The master node will then wait until X slave nodes has connected before the test is started.

Running distributed with Docker¶

See Running Locust with Docker