nova scheduler: Failed to schedule_run_instance: No valid host was found

Asked by Sumit Sengupta on 2012-04-03

The nova-scheduler during creation of an instance is throwing issue 'Failed to schedule_run_instance: No valid host was found.' This is failing at when it checks that host passes filters or not. Any idea what could be the reason and how to resolve this?
2012-04-03 12:37:20 DEBUG nova.scheduler.host_manager [req-49ea5605-9e31-4db6-955c-8acd59cf0f82 baaa0b3c108b4626a083007a72d37b01 4eabbf34471d469a91234b769b5b2af3] Host filter function <bound method RamFilter.host_passes of <nova.scheduler.filters.ram_filter.RamFilter object at 0x4217150>> failed for mymachine-host from (pid=4567) passes_filters /home/myuser/openstack/nova/app/nova/scheduler/

2012-04-03 12:37:20 WARNING nova.scheduler.manager [req-49ea5605-9e31-4db6-955c-8acd59cf0f82 baaa0b3c108b4626a083007a72d37b01 4eabbf34471d469a91234b769b5b2af3] Failed to schedule_run_instance: No valid host was found.

2012-04-03 12:37:20 WARNING nova.scheduler.manager [req-49ea5605-9e31-4db6-955c-8acd59cf0f82 baaa0b3c108b4626a083007a72d37b01 4eabbf34471d469a91234b769b5b2af3] Setting instance c6ef30e4-ae64-46b8-aab9-700d3e68165a to ERROR state.

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John Garbutt (johngarbutt) said : #1

It is worth talking a look in the database service table to ensure the compute service is correctly reporting its stats.

It looks a bit like nova thinks you don't have enough RAM to launch your instance.

Vish Ishaya (vishvananda) said : #2

You can tell the scheduler to overcommit ram using ram_allocation_ratio:

###### (FloatOpt) virtual ram to physical ram allocation ratio
# ram_allocation_ratio=1.5

yong sheng gong (gongysh) said : #3

I am not sure about the host status. Maybe you should first run nova-manager service-list to check if there are nova-compute smiling. And then try a tiny flavor instance.

hope it can help.

Sumit Sengupta (sumit-sngpt) said : #4

Solved this by adding following in my nova.conf then restarting openstack. No issues yet but not sure about its side affects.


Let me know if there would be any issue.

drolfe (drolfe) said : #5

Issue fixed for me

I've had similar errors on my dev openstack deployment , adding


to nova.conf on the node running the scheduler service fixed the issue

I'm gussing the default filter didn't like the hypervisor for some reason ?

Hello, I tried adding --scheduler_default_filters=AllHostsFilter to nova.conf, reboot, no success...

Failed to schedule_run_instance: No valid host was found.

nova-manage host list
host zone
2012-07-16 15:13:17 DEBUG nova.utils [req-1bcaad5f-e732-4587-80a6-761ae93d79fa None None] backend <module 'nova.db.sqlalchemy.api' from '/usr/lib/python2.7/dist-packages/nova/db/sqlalchemy/api.pyc'> from (pid=2895) __get_backend /usr/lib/python2.7/dist-packages/nova/
XEN01 nova

Ubuntu 12.04
Followed setup of stackgeek

any developments?

Sampat Ponnaganti (sampat-p) said : #7

I had to set (Icehouse)
scheduler_default_filters = ComputeFilter
ComputeFilter by default returns all hosts so the scheduler will return some instance.

RamFiler as per my knowledge sums up Ram usage of running/suspended...etc except Error state instance flavors. So if you have bunch of suspended instances you cannot spawn any more instances.

Rupesh Chowdhary (rupeshrams) said : #8

There is two possibilities of this issue cause,

1. While launch the instance need to give the --availability-zone to specify the instance launch.

nova boot --image 52459jlrw4k4l --flavor small --nic net-id=540545lkjgd--dngg-lkjlkj52525 test01 --availability-zone kvm1

2. In controller node check the filter as updated properly or not . /etc/nova/nova.conf validate the information at scheduler_default_filters= ( filters must be mention here)

3. In last case check the filter is exist in filters directory or not in the following path, file should be there in the path

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