Add Support for DB2 (v10.5+)

https://blueprints.launchpad.net/nova/+spec/db2-database

The community currently supports MySQL and PostgreSQL production databases. Several other core projects already support DB2 (Keystone, Glance, Neutron, Ceilometer, Heat). This blueprint adds support to Nova for DB2 as a production database.

Problem description

  • Currently there is no support in the community for a deployer to run Nova against a DB2 backend database.
  • For anyone running applications against an existing DB2 database that wants to move to OpenStack, they’d have to use a different database engine to run Nova in OpenStack.
  • There is currently an inconsistent support matrix across the core projects since the majority of core projects support DB2 but Nova does not yet.

Proposed change

Add code to support migrating the Nova database against a DB2 backend. This would require a fresh deployment of Nova since there are no plans to migrate an existing Nova database from another engine, e.g. MySQL, to DB2.

Unit test code would also be updated to support running tests against a DB2 backend with the ibm_db_sa driver and all Nova patches will be tested against a Tempest full run with 3rd party CI running DB2 that IBM will maintain.

There is already some code in Oslo’s db.api layer to support common function with DB2 like duplicate entry error handling and connection trace, so that is not part of this spec.

Alternatives

Deployers can use other supported database backends like MySQL or PostgreSQL, but this may not be an ideal option for customers already running applications with DB2 that want to integrate with OpenStack. In addition, you could run other core projects with multiple schemas in a single DB2 OpenStack database, but you’d have to run Nova separately which is a maintenance/configuration problem.

Data model impact

  1. The 216 migration will be updated to handle conditions with DB2 like index and foreign key creation. The main issue here is that DB2 does not support unique constraints over nullable columns, it will instead create a unique index that excludes null keys. Most unique constraints created in Nova are on non-nullable columns, but the instances.uuid column is nullable and the 216 migration creates a unique index on it, but this will not allow any foreign keys on the instances.uuid column to be created with DB2 since the reference column has to be a unique or primary key constraint.
  2. In order to support creating the same foreign keys that reference the instances.uuid column as other database engines, the instances.uuid column must be made non-nullable and a unique constraint must be created on it. The dependent blueprint “Enforce unique instance uuid in data model” is used to handle this change.
  3. Finally, add another migration script which creates the previously excluded foreign keys from the 216 migration script for DB2.

REST API impact

None.

Security impact

None.

Notifications impact

None.

Other end user impact

None.

Performance Impact

The only performance impact on existing deployments is in the migration script changes which would be tested with turbo-hipster.

Other deployer impact

The new database migration which creates the missing foreign keys since the control node needs to be down when running the migration. However, the new migration only creates foreign keys if the backend is DB2, which would be a new installation as noted in the “Proposed change” section so the impact should be minimal.

Developer impact

The only impact on developers is if they are adding DB API code or migrations that do not work with DB2 they will have to adjust those appropriately, just like we do today with MySQL and PostgreSQL. IBM active technical contributors would provide support/guidance on issues like this which require specific conditions for DB2, although for the most part the DB2 InfoCenter provides adequate detail on how to work with the engine and provides details on error codes.

Implementation

Assignee(s)

Primary assignee:
mriedem@us.ibm.com

Work Items

  1. Change the 216 migration to work with DB2.
  2. Add a new migration to create the excluded foreign keys from the 216 script for DB2.
  3. Make the test_migrations.py module work with a configured DB2 backend for running unit tests.

See the WIP patch for details: https://review.openstack.org/#/c/69047/

Dependencies

  • Blueprint “Enforce unique instance uuid in data model”: https://blueprints.launchpad.net/nova/+spec/enforce-unique-instance-uuid-in-db
  • DB2 10.5 support was added to sqlalchemy-migrate 0.9 during Icehouse: https://blueprints.launchpad.net/sqlalchemy-migrate/+spec/add-db2-support
  • There are no requirements changes in Nova for the unit tests to work. The runtime requirements are the ibm-db-sa and ibm_db modules, which are both available from pypi. sqlalchemy-migrate optionally imports ibm-db-sa. The ibm-db-sa module requires a natively compiled ibm_db which has the c binding that talks to the DB2 ODBC/CLI driver.
  • Note that only DB2 10.5+ is supported since that’s what added unique index support over nullable columns which is how sqlalchemy-migrate handles unique constraints over nullable columns.

Testing

There are three types of testing requirements, Tempest, unit test and turbo-hipster performance/scale tests. Each have different timelines for when they are proposed to be implemented.

  • IBM is already running 3rd party CI for DB2 on the existing Nova WIP patch that adds DB2 support. The same 3rd party CI is running against all sqlalchemy-migrate changes with DB2 on py26/py27 and runs Tempest against Keystone/Glance/Cinder/Heat patches with a DB2 backend. Once the DB2 support is merged the DB2 3rd party CI would run against all Nova patches with a full Tempest run. This is considered required testing for this blueprint to merge in the Juno release.
  • While code will be added to make the Nova unit tests work against a DB2 backend, running Nova unit tests against DB2 with third party CI is not considered in the scope of this blueprint for Juno, but long-term this is something IBM wants to get running for additional QA coverage for DB2 in Nova. This is something that would be worked on after getting Tempest running. The plan for delivering third party unit test coverage is in the K release.
  • Running 3rd party turbo-hipster CI against DB2 is not in plan for this blueprint in Juno but like running unit tests against DB2 in 3rd party CI, running turbo-hipster against DB2 in 3rd party CI would be a long-term goal for QA and the IBM team will work on that after Tempest is running and after unit test CI is worked on. The plan for delivering third party turbo-hipster performance test coverage is in the K release.
  • The proposed penalty for failing to deliver third party unit test and/or turbo-hipster performance test coverage in the K release is that the Nova team will turn off voting/reporting of DB2 third party CI and not allow DB2 fixes to Nova until the third party CI is available.
  • More discussion in the mailing list here: http://lists.openstack.org/pipermail/openstack-dev/2014-May/035009.html

Documentation Impact

References