Cloned from launchpad blueprint https://blueprints.launchpad.net/nova/+spec/internal-scheduler.

Description:

Currently, NoValidHost exception happend without any detail information.
The only way to find out the reason is looking through nova logs. But if there 
are thousands of host, it will make sysadmin crazy.

So the blueprint propose an API to show internal information of scheduler process.
The API shows the filter result of each host and the reason why the host is failed.

The API looks like bellow:

GET /v2/{tenant}/servers/{instance}/os-schedule-info

{
    "schedule_info": [
        {
            "host": "ops1",
            "result": "failed",
            "reason": "does not have 16384 MB usable ram, it only has -106745.0 MB usable ram",
            "created_at": "2013-06-01 01:01:02.000"
        },
        {
            "host": "ops2",
            "result": "failed",
            "reason": "blablabla",
           "created_at": "2013-06-01 01:01:03.000"
        },
        {
            "host": "ops3",
            "result": "passed",
           "created_at": "2013-06-01 01:01:04.000"
        }
    ]
}

Specification URL (additional information):

None