Zero-Downtime Deployments: A Practical Guide

Downtime during deployments is no longer acceptable. Users expect applications to be available 24/7, and even a few minutes of downtime can result in lost revenue, damaged trust, and frustrated customers. The good news is that achieving zero-downtime deployments is more accessible than ever.

Rolling Deployments

Rolling deployments gradually replace old instances with new ones. At any point during the deployment, some instances run the old version while others run the new version. The load balancer ensures traffic only reaches healthy instances.

• Advantages: Simple to implement, minimal resource overhead
• Risks: Two versions run simultaneously, requiring backward-compatible changes
• Best for: Stateless web applications and API servers

Blue-Green Deployments

Blue-green deployments maintain two identical environments. The “blue” environment runs the current version, while the “green” environment is updated with the new version. Once the green environment is tested and verified, traffic is switched instantly.

• Advantages: Instant rollback by switching traffic back, full testing before go-live
• Risks: Requires double the infrastructure during deployment
• Best for: Critical applications where rollback speed is paramount

Canary Releases

Canary releases route a small percentage of traffic to the new version while monitoring for errors. If metrics look good, traffic is gradually shifted until 100% reaches the new version. If problems are detected, traffic is immediately rolled back.

• Advantages: Minimal blast radius, real-world testing with actual users
• Risks: Requires sophisticated traffic routing and monitoring
• Best for: Large-scale applications with significant user impact

Database Migrations

The trickiest part of zero-downtime deployments is database migrations. The golden rule: never make breaking schema changes in a single deployment. Instead, use a multi-step approach. First deploy code that works with both old and new schemas. Then run the migration. Finally, deploy code that uses only the new schema.

How CloudNest Handles It

CloudNest implements rolling deployments by default for all applications. Each deployment creates new instances, waits for health checks to pass, and then gradually shifts traffic. If any instance fails its health check, the deployment is automatically rolled back.

With instant rollbacks, preview deployments, and built-in health checks, zero-downtime deployments are not a luxury — they are the default experience on CloudNest.