Isolating tenants in a multi-tenant cloud system includes identifying a plurality of tenants in the multi-tenant cloud system, assigning a domain to each tenant of the plurality of tenants based on a wavelength division multiplexing (WDM), for each wavelength set of the plurality of wavelength sets, associating each wavelength set with a different domain of the plurality of domains and with a different indicator identifying the domain for the wavelength set, and isolating each tenant using the associated wavelength sets and associated indicators. The plurality of tenants share computational resources in the multi-tenant cloud system and the domain includes the computational resources for each tenant. The WDM uses a plurality of wavelength sets and each wavelength set includes one or more wavelengths.