This tag is part of the assert category of tags, which are assertions made by the project team themselves about the maturity of their deliverables.

The assert:supports-zero-downtime-upgrade tag asserts that in addition to a deliverable supporting minimal rolling upgrade capabilities, it does so without incurring any disruption to API availability.

Application to current deliverables


No projects are using assert:supports-zero-downtime-upgrade, yet.


OpenStack components represent code that is installed and deployed on many distributed systems in order to provide services to users. Operators need to know what services support an upgrade process that eliminates downtime of the control plane entirely.


  • The deliverable is a software component of an OpenStack cloud (openstack, openstack-operations on the map) delivering a long-lived service with an API.

  • The deliverable has already successfully asserted both the assert:supports-upgrade and assert:supports-rolling-upgrade tags. All the requirements for those tags are requirements for this tag, and assertion of both those tags are requirements to assert this tag.

  • In addition to the plan required by the assert:supports-rolling-upgrade tag which allows for minimal downtime, this tag requires services to completely eliminate API downtime of the control plane during the upgrade. In other words, requiring operators to “restart all API services together” is not reasonable under this tag. Additionally, it is not reasonable for services to respond to requests with HTTP 5xx codes when they otherwise would have returned successful responses, even intermittently.

  • While all requests to the control plane must be eventually processed, performance degradation during the upgrade is acceptable. This may include slow HTTP responses and delayed request handling (such as messages queuing up on the message bus).

  • In addition to the full stack integration testing required by the assert:supports-rolling-upgrade tag, services should be capable of receiving and handling requests throughout the rolling upgrade process with a normal success rate. In order to assert this tag, services should prevent regression by implementing a zero-downtime gate job wherein both a new version of the service and an old version of the service are run concurrently.