Translating Diego Resource to Mesos Resource

[ilackarms]

There's no clear translation between Diego's concept of a Resource, and Mesos' concept of a resource:

cloudfoundry-mesos/scheduler/scheduler_interface.go

Line 9 in 85dcd82

// TODO: how to allocate cpu since no cpu requirement in diego auction

We should look into ways to determine the CPU requirement of a Diego task and the Container Capacity of a Mesos Resource Offer.

[jianhuiz]

Diego calculates CPU weights based on app memory usage (256MB8192MB => 1100).

In order to mimic this situation, a possible solution could be allocate the CPU at the same proportion of the memory required vs. memory Offered. E.g. allocate 0.5 CPU for a app that requires 1GB memory against an offer with 4 CPUs and 8GB memory, as a result this app gets 1/8 of CPUs and 1/8 of memory. A second app that requires 2GB memory will get 1 CPU, or let's say 0.5 CPU per GB memory.

In Mesos environment, the resource could be used by other frameworks, which means the free CPU Memory ratio will change, in order to get a fairness CPU allocation for all the Diego apps (on the same slave), the CPU allocation per GB memory should be calculated and remain constant when the first task was launched on a slave.