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diff --git a/design_docs/report-host-fault-to-update-server-state-immediately.rst b/design_docs/report-host-fault-to-update-server-state-immediately.rst new file mode 100644 index 00000000..0ee02064 --- /dev/null +++ b/design_docs/report-host-fault-to-update-server-state-immediately.rst @@ -0,0 +1,233 @@ +==================================================== +Report host fault to update server state immediately +==================================================== + +https://blueprints.launchpad.net/nova/+spec/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: + + /v2.1/{tenant_id}/os-hosts/{host_name} + + 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: + +* Compute API extensions documentation. + http://developer.openstack.org/api-ref-compute-v2.1.html +* Nova commands documentation. + http://docs.openstack.org/user-guide-admin/content/novaclient_commands.html +* Compute command-line client documentation. + http://docs.openstack.org/cli-reference/content/novaclient_commands.html +* nova.compute.api documentation. + http://docs.openstack.org/developer/nova/api/nova.compute.api.html +* High Availability guide might have page to tell external tool could provide + ability to provide faster HA as able to update states by new API. + http://docs.openstack.org/high-availability-guide/content/index.html + +References +========== +* OPNFV Doctor project: https://wiki.opnfv.org/doctor +* OpenStack Instance HA Proposal: + http://blog.russellbryant.net/2014/10/15/openstack-instance-ha-proposal/ +* The Different Facets of OpenStack HA: + http://blog.russellbryant.net/2015/03/10/ + the-different-facets-of-openstack-ha/ |