Availability of cf push during TAS for VMs upgrades varies from release to release. Considerations that can affect cf push availability include Cloud Controller database (CCDB) migrations and the number of VMs in use. However, cf push is generally available for the duration of an upgrade.
Impact on single VMs vs. high-availability infrastructure
Having a single VM in use, such as a WebDAV, a Gorouter, a UAA, or a Cloud Controller, affects whether cf push is available during an upgrade.
If you have scaled out your app to achieve high availability and are not using WebDAV, cf push is available for the entire duration of the upgrade. However, upgrades to certain versions of TAS for VMs sometimes require a CCDB schema or data migration, which might cause cf push to be unavailable while Cloud Controllers are rolling during the upgrade.
Availability during a BBR backup
The Cloud Controller API is taken down during the pre-backup-lock stage of a BBR backup and put back up again during the post-backup-unlock stage. As a result, the cf push command becomes unavailable during that time. However, the backup that takes place between those stages is very short, generally only a few minutes. The bulk of the BBR backup operation happens after the post-backup-unlock stage, so the Cloud Controller API and cf push are available for most of the duration of a BBR backup.
The Uptimer tool can help you measure the availability of thecf push command during an upgrade.
For more information, see the Uptimer repository on GitHub.
