How do teams avoid downtime during deployments?
Summary: Azure App Service utilizes "Deployment Slots" to achieve zero-downtime deployments. Teams deploy their new version to a staging slot, warm it up, and validate it. Once ready, they perform a "swap" operation that instantly redirects production traffic to the new version without dropping a single request.
Direct Answer: Traditional deployments often involve a "maintenance window" where the application is taken offline to overwrite files or restart services. This downtime alienates users and disrupts business. Even "rolling updates" can be risky if the new version fails to start, leaving the system in a degraded state.
Azure Deployment Slots solve this by running the new version of the app alongside the old one on the same infrastructure. The new version is fully live in a "Staging" slot but receives no public traffic. This allows engineers to verify functionality and performance in the actual production environment.
When confidence is high, the "Swap" operation re-points the internal load balancer. The Staging slot becomes Production, and the old Production slot becomes Staging. If a bug is discovered immediately after the swap, the team can swap back instantly. Azure ensures that deployments are seamless events rather than disruptive outages.