On Thu, Aug 25, 2016 at 1:13 PM, Steve Martinelli <s.martine...@gmail.com> wrote:
> The keystone team is pursuing a trigger-based approach to support rolling, > zero-downtime upgrades. The proposed operator experience is documented here: > > http://docs.openstack.org/developer/keystone/upgrading.html > > This differs from Nova and Neutron's approaches to solve for rolling > upgrades (which use oslo.versionedobjects), however Keystone is one of the > few services that doesn't need to manage communication between multiple > releases of multiple service components talking over the message bus (which > is the original use case for oslo.versionedobjects, and for which it is > aptly suited). Keystone simply scales horizontally and every node talks > directly to the database. > > Database triggers are obviously a new challenge for developers to write, > honestly challenging to debug (being side effects), and are made even more > difficult by having to hand write triggers for MySQL, PostgreSQL, and > SQLite independently (SQLAlchemy offers no assistance in this case), as > seen in this patch: > > https://review.openstack.org/#/c/355618/ > > However, implementing an application-layer solution with > oslo.versionedobjects is not an easy task either; refer to Neutron's > implementation: > > https://review.openstack.org/#/q/topic:bp/adopt-oslo- > versioned-objects-for-db > > Our primary concern at this point are how to effectively test the triggers > we write against our supported database systems, and their various > deployment variations. We might be able to easily drop SQLite support (as > it's only supported for our own test suite), but should we expect variation > in support and/or actual behavior of triggers across the MySQLs, MariaDBs, > Perconas, etc, of the world that would make it necessary to test each of > them independently? If you have operational experience working with > triggers at scale: are there landmines that we need to be aware of? What is > it going to take for us to say we support *zero* dowtime upgrades with > confidence? > > Steve & Dolph > > No experience to add for triggers, but I'm happy to help test this on a MySQL Galera cluster. I'd also like to add thanks for looking into this. A keystone outage is a cloud outage and being able to eliminate them from upgrades will be beneficial to everyone.
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