The maximum number of job instances that a Worker can run is specified by the worker_cpus parameter. This value can be set in either the worker's local qb.conf file, or the centrally-managed qbwrk.conf file.
By default, Qube sets the number of job slots equal to the number of CPU cores on the system.
In this example, set the number of job slots to 2:
worker_cpus = 2