CPU instance constraints not working as expected

[Tom Haddon]

--constraints "cpu-cores=1 mem=4G arch=amd64" gets 4 core machine, even when a flavor matching the exact instance exists:

(clupdown)prodstack-u1@wekufe:~$ nova flavor-list | grep cpu1-ram4-disk50-ephemeral20
| 1103 | cpu1-ram4-disk50-ephemeral20 | 4096 | 50 | 20 | | 1 | 1.0 | True | {} |

[Sidnei da Silva (sidnei)]

Initial findings:

In the openstack provider, 'Cost' is set to RAM:

    Cost: uint64(flavor.RAM),

When finding instance types, we are sorting by Cost:

   sort.Sort(byCost(itypes))

But all costs being the same, it's actually taking the original order into account, which I assume might be busting the computation.

A suggestion is to include the number of cores into the cost for the openstack provider, such that if two machines have the same amount of RAM, the one with the less number of cores that matches the cpu-cores constraint is picked first.

[Sidnei da Silva (sidnei)]

Verification:

$ nova flavor-list | grep ram4
| 1003 | cpu1-ram4-disk10-ephemeral20 | 4096 | 10 | 20 | | 1 | 1.0 | True | {} |
| 1013 | cpu2-ram4-disk10-ephemeral20 | 4096 | 10 | 20 | | 2 | 1.0 | True | {} |
| 1023 | cpu3-ram4-disk10-ephemeral20 | 4096 | 10 | 20 | | 3 | 1.0 | True | {} |
| 1033 | cpu4-ram4-disk10-ephemeral20 | 4096 | 10 | 20 | | 4 | 1.0 | True | {} |

$ juju deploy --constraints="cpu-cores=1 mem=4G" ubuntu
$ nova show 93bf2782-701a-44ec-8632-04215f94b2ab | grep flavor
| flavor | cpu1-ram4-disk10-ephemeral20 (1003)

$ juju deploy --constraints="cpu-cores=2 mem=4G" ubuntu ubuntu2
$ nova show e5b40610-f796-4860-aa7f-97d75ffe63e0 | grep flavor
| flavor | cpu2-ram4-disk10-ephemeral20 (1013)

Seems good to go.

[Sidnei da Silva (sidnei)]

Double checking. Without the fix, got:

$ juju -v deploy --constraints="cpu-cores=1 mem=4G" ubuntu ubuntu1
$ nova show 7c99e0ce-5044-4e50-aeab-7f15e9b79c65 | grep flavor
| flavor | cpu3-ram4-disk10-ephemeral20 (1023)

$ juju deploy --constraints="cpu-cores=2 mem=4G" ubuntu ubuntu2
$ nova show ca0383cf-b553-4052-8056-d3793aedde5b
| flavor | m1.medium (3)

With the attached branch, confirmed working per previous comment.