diff --git a/specs/newton/approved/async-live-migration-rest-check.rst b/specs/newton/approved/async-live-migration-rest-check.rst new file mode 100644 index 000000000..d3a96a7c8 --- /dev/null +++ b/specs/newton/approved/async-live-migration-rest-check.rst @@ -0,0 +1,166 @@ +.. + This work is licensed under a Creative Commons Attribution 3.0 Unported + License. + + http://creativecommons.org/licenses/by/3.0/legalcode + +======================================= +Make checks before live-migration async +======================================= + +https://blueprints.launchpad.net/nova/+spec/async-live-migration-rest-check + +The existing nova live-migration operation is complex: verification of +the environment is required before accepting and triggering the live-migration. +This verification is done in a synchronous manner with several RPC calls that +must all be successful before the process can begin and the REST API layer can +respond. It would be better to make the checks asynchronous and have the REST +API respond with an immediate `202 - Accepted`. + + +Problem description +=================== + +The existing workflow for the environment verification required before a +live-migration involves several steps: an RPC call is made to the conductor +which triggers two more RPC calls to the relevant compute nodes. Only once +those are okay is there an RPC cast to trigger the migration and a response to +the HTTP request. + + +Use Cases +--------- + +A user doing a live migration would like to have a fast response to a +live-migration request and use the `instance-actions` service to get valid +status. + +Proposed change +=============== + +Instead of doing all the checks in a block way, this spec proposes to record +the conductor's method with `wrap_instance_event` so it will be possible to +check live-migration status. Upon receiving a request for a live-migration +the Nova API will send an RPC cast to the conductor and then respond +immediately with the HTTP response. To separate blocking and non-blocking +live-migration types new method will be introduced to conductor's RPC API: +* migrate_server - existing general method for cold migration, resize and +live-migration. This will continue providing existing blocking behaviour, by +sending RPC call from Nova API to conductor. +* live_migrate_server - new method for live-migration only. This method will +implement non-blocking checks by using rpc cast from the Nova API layer. +Both methods should be decorated with `wrap_instance_event`, so events will be +recorded to database for blocking and non-blocking paths too. + + +Alternatives +------------ + +Leave things as they are. Another alternative would be to switch to +non-blocking rpc cast without maintaining previous behavior and bumping Nova +REST API microversion. + +Data model impact +----------------- + +None + +REST API impact +--------------- + +As this change will cause verification checks to be done in the background, the +number of cases in which the live-migration API will respond with +`badRequest(400)` will be limited to receipt of bad input. REST API +microversion should be bumped, to retain possibility of switching to previous +behaviour. + +Security impact +--------------- + +None + +Notifications impact +-------------------- + +None + +Other end user impact +--------------------- + +Users should check live-migration status, using `instance-actions` operation. + +Performance Impact +------------------ + +Nova REST API method becomes non-blocking, which should increase overall +throughput of the API layer. At the same time more writes to database should be +added(writing instance actions details on conductor's side). + +Other deployer impact +--------------------- + +None + +Developer impact +---------------- + +None + + +Implementation +============== + +Assignee(s) +----------- + +Primary assignee: + tdurakov + +Other contributors: + rpodolyaka + +Work Items +---------- + +* Add `wrap_instance_event` decorator to conductor's methods +* Make live-migration checks nonblocking +* Bump Nova REST API version. + + +Dependencies +============ + +None + + +Testing +======= + +Test for checking that conductor's part of live-migration is recorded by +instance-actions should be added to tempest. Also code should be covered by +unit and functional tests too. + + +Documentation Impact +==================== + +As this change changes workflow, docs should be updated. It's needed to +highlight to the end user that it's required to check live-migration process +over `instance-actions`. + +References +========== + +* https://review.openstack.org/#/c/314932/ - PoC + + +History +======= + +.. list-table:: Revisions + :header-rows: 1 + + * - Release Name + - Description + * - Newton + - Introduced

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