Zero-Downtime Deployment
Zero-downtime deployment is a deployment strategy where software updates are applied without interrupting the running service – users do not notice the update.
Maintenance windows at 3 a.m., notices about planned outages, users clicking into nothing – that used to be normal. Modern web applications are updated without noticeable interruption. Zero-downtime deployment makes it possible: the new version is started alongside the old one, traffic is shifted gradually and if there are problems you roll back immediately. For business-critical applications this practice is essential.
What is Zero-Downtime Deployment?
Zero-downtime deployment (also no-downtime deployment) refers to deployment strategies that keep an application available during a software update. Approaches include: blue-green (two identical environments, traffic is switched), rolling (instances updated one after another), canary (new version only for a small fraction of users first) and feature flags (features turned on/off in code without a new deployment). Prerequisites are an architecture that supports multiple instances and backward-compatible database migrations.
How does Zero-Downtime Deployment work?
Example blue-green: Two identical production environments (blue and green) run in parallel. The current version runs on blue and receives live traffic. The new version is deployed to green and tested there. When all tests pass, the load balancer switches traffic from blue to green – in a fraction of a second. If there are problems, traffic is switched back to blue (instant rollback). With rolling deployment, instances are updated one by one: while one is updated, the others serve traffic. With canary, only 5–10% of traffic goes to the new version first; metrics are watched and the share is increased gradually.
Practical Examples
An online shop deploys new features daily with blue-green: customers notice nothing, and if something breaks rollback is under 30 seconds.
A SaaS vendor uses canary: new features go first to 5% of users. If error rates and performance are good, rollout goes to 100%.
A Kubernetes cluster does rolling updates: pods are updated one by one, with health checks ensuring only healthy pods receive traffic.
A banking portal uses feature flags: the new transfer feature is already deployed but disabled. After UAT approval it is enabled via a flag – no new deployment.
Typical Use Cases
E-commerce: Shops cannot afford to be offline during business hours – revenue loss per minute of downtime
SaaS: Global users in different time zones expect 24/7 availability
Financial services: Regulatory requirements for availability and fast rollback
Continuous delivery: Teams that deploy daily or more need strategies that avoid downtime
Microservices: Individual services are updated independently without affecting the whole system
Advantages and Disadvantages
Advantages
- No downtime: Users do not notice the deployment – the system stays available
- Instant rollback: If there are problems, switch back to the previous version in seconds
- Higher deployment frequency: When deployments are low-risk, teams can release more often
- Better user experience: No maintenance windows, no outage notices, no lost sessions
- Lower risk: Canary deployments find problems early before all users are affected
Disadvantages
- Infrastructure complexity: Blue-green needs double infrastructure; canary needs smart traffic routing
- Database migrations: Schema changes must be backward-compatible – that needs careful planning
- Monitoring: Automatic rollbacks need solid monitoring and clear health checks
- Cost: Extra infrastructure (blue-green) or more complex pipelines increase operating cost
Frequently Asked Questions about Zero-Downtime Deployment
Which deployment strategy is best?
How do you handle database migrations with zero downtime?
Do you need Kubernetes for zero-downtime deployment?
Related Terms
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