A computer apparatus for associating a virtual machine, VM, with a computing resource, the apparatus comprising: a memory arranged to store: an anti-affinity rule indicating that a first VM (235 1) is to be separated from a second VM (235 2) during execution of the first and second VMs (235 1, 235 2), wherein the first VM (235 1) is associated with a first computing resource (305 1) of a plurality of computing resources (305, 340); and a processor coupled to the memory, the apparatus characterized in that: the memory is further arranged to store a first failure correlation between the first computing resource (305 1) and a second computing resource (305 2) of the plurality of computing resources, the first failure correlation representing a probability that a failure of the first computing resource (305 1) will be concurrent with a failure of the second computing resource (305 2); and the processor is programmed to: determine a second failure correlation between the first computing resource (305 1) and a third computing resource (305 3) of the plurality of computing resources, the second failure correlation representing a probability that a failure of the first computing resource (305 1) will be concurrent with a failure of the third computing resource (305 3), wherein the second failure correlation is less than the first failure correlation; and associate the second VM (235 2) with the third computing resource (305 3) based on the anti-affinity rule and the second failure correlation being less than the first failure correlation. a memory arranged to store: an anti-affinity rule indicating that a first VM (235 1) is to be separated from a second VM (235 2) during execution of the first and second VMs (235 1, 235 2), wherein the first VM (235 1) is associated with a first computing resource (305 1) of a plurality of computing resources (305, 340); and a processor coupled to the memory, an anti-affinity rule indicating that a first VM (235 1) is to be separated from a second VM (235 2) during execution of the first and second VMs (235 1, 235 2), wherein the first VM (235 1) is associated with a first computing resource (305 1) of a plurality of computing resources (305, 340); and a processor coupled to the memory, the apparatus characterized in that: the memory is further arranged to store a first failure correlation between the first computing resource (305 1) and a second computing resource (305 2) of the plurality of computing resources, the first failure correlation representing a probability that a failure of the first computing resource (305 1) will be concurrent with a failure of the second computing resource (305 2); and the processor is programmed to: determine a second failure correlation between the first computing resource (305 1) and a third computing resource (305 3) of the plurality of computing resources, the second failure correlation representing a probability that a failure of the first computing resource (305 1) will be concurrent with a failure of the third computing resource (305 3), wherein the second failure correlation is less than the first failure correlation; and associate the second VM (235 2) with the third computing resource (305 3) based on the anti-affinity rule and the second failure correlation being less than the first failure correlation. the memory is further arranged to store a first failure correlation between the first computing resource (305 1) and a second computing resource (305 2) of the plurality of computing resources, the first failure correlation representing a probability that a failure of the first computing resource (305 1) will be concurrent with a failure of the second computing resource (305 2); and the processor is programmed to: determine a second failure correlation between the first computing resource (305 1) and a third computing resource (305 3) of the plurality of computing resources, the second failure correlation representing a probability that a failure of the first computing resource (305 1) will be concurrent with a failure of the third computing resource (305 3), wherein the second failure correlation is less than the first failure correlation; and associate the second VM (235 2) with the third computing resource (305 3) based on the anti-affinity rule and the second failure correlation being less than the first failure correlation. determine a second failure correlation between the first computing resource (305 1) and a third computing resource (305 3) of the plurality of computing resources, the second failure correlation representing a probability that a failure of the first computing resource (305 1) will be concurrent with a failure of the third computing resource (305 3), wherein the second failure correlation is less than the first failure correlation; and associate the second VM (235 2) with the third computing resource (305 3) based on the anti-affinity rule and the second failure correlation being less than the first failure correlation.