This is a specification draft of a blueprint proposed for OpenStack Nova Liberty. It was written by project member(s) and agreed within the project before submitting it upstream. No further changes to its content will be made here anymore; please follow it upstream:

Original draft is as follow:

1.1.1. Report host fault to update server state immediately

A new API is needed to report a host fault to change the state of the instances and compute node immediately. This allows usage of evacuate API without a delay. The new API provides the possibility for external monitoring system to detect any kind of host failure fast and reliably and inform OpenStack about it. Nova updates the compute node state and states of the instances. This way the states in the Nova DB will be in sync with the real state of the system. Problem description

  • Nova state change for failed or unreachable host is slow and does not reliably state compute node is down or not. This might cause same instance to run twice if action taken to evacuate instance to another host.

  • Nova state for instances on failed compute node will not change, but remains active and running. This gives user a false information about instance state. Currently one would need to call “nova reset-state” for each instance to have them in error state.

  • OpenStack user cannot make HA actions fast and reliably by trusting instance state and compute node state.

  • As compute node state changes slowly one cannot evacuate instances. Use Cases

Use case in general is that in case there is a host fault one should change compute node state fast and reliably when using DB servicegroup backend. On top of this here is the use cases that are not covered currently to have instance states changed correctly: * Management network connectivity lost between controller and compute node. * Host HW failed.

Generic use case flow:

  • The external monitoring system detects a host fault.

  • The external monitoring system fences the host if not down already.

  • The external system calls the new Nova API to force the failed compute node into down state as well as instances running on it.

  • Nova updates the compute node state and state of the effected instances to Nova DB.

Currently nova-compute state will be changing “down”, but it takes a long time. Server state keeps as “vm_state: active” and “power_state: running”, which is not correct. By having external tool to detect host faults fast, fence host by powering down and then report host down to OpenStack, all these states would reflect to actual situation. Also if OpenStack will not implement automatic actions for fault correlation, external tool can do that. This could be configured for example in server instance METADATA easily and be read by external tool. Project Priority

Liberty priorities have not yet been defined. Proposed change

There needs to be a new API for Admin to state host is down. This API is used to mark compute node and instances running on it down to reflect the real situation.

Example on compute node is:

  • When compute node is up and running: vm_state: active and power_state: running nova-compute state: up status: enabled

  • When compute node goes down and new API is called to state host is down: vm_state: stopped power_state: shutdown nova-compute state: down status: enabled

vm_state values: soft-delete, deleted, resized and error should not be touched. task_state effect needs to be worked out if needs to be touched. Alternatives

There is no attractive alternatives to detect all different host faults than to have a external tool to detect different host faults. For this kind of tool to exist there needs to be new API in Nova to report fault. Currently there must have been some kind of workarounds implemented as cannot trust or get the states from OpenStack fast enough. Data model impact

None REST API impact

  • Update CLI to report host is down

    nova host-update command

    usage: nova host-update [–status <enable|disable>]

    [–maintenance <enable|disable>] [–report-host-down] <hostname>

    Update host settings.

    Positional arguments

    <hostname> Name of host.

    Optional arguments

    –status <enable|disable> Either enable or disable a host.

    –maintenance <enable|disable> Either put or resume host to/from maintenance.

    –down Report host down to update instance and compute node state in db.

  • Update Compute API to report host is down:


    Normal response codes: 200 Request parameters

    Parameter Style Type Description host_name URI xsd:string The name of the host of interest to you.

    “host”: {

    “status”: “enable”, “maintenance_mode”: “enable” “host_down_reported”: “true”



    “host”: {

    “host”: “65c5d5b7e3bd44308e67fc50f362aee6”, “maintenance_mode”: “enabled”, “status”: “enabled” “host_down_reported”: “true”



  • New method to nova.compute.api module HostAPI class to have a to mark host related instances and compute node down: set_host_down(context, host_name)

  • class novaclient.v2.hosts.HostManager(api) method update(host, values) Needs to handle reporting host down.

  • Schema does not need changes as in db only service and server states are to be changed. Security impact

API call needs admin privileges (in the default policy configuration). Notifications impact

None Other end user impact

None Performance Impact

Only impact is that user can get information faster about instance and compute node state. This also gives possibility to evacuate faster. No impact that would slow down. Host down should be rare occurrence. Other deployer impact

Developer can make use of any external tool to detect host fault and report it to OpenStack. Developer impact

None Implementation Assignee(s)

Primary assignee: Tomi Juvonen Other contributors: Ryota Mibu Work Items

  • Test cases.

  • API changes.

  • Documentation. Dependencies

None Testing

Test cases that exists for enabling or putting host to maintenance should be altered or similar new cases made test new functionality. Documentation Impact

New API needs to be documented: References