What are the different deployment strategies used in CI/CD? When would you use each one?

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Different deployment strategies offer various tradeoffs between risk, speed, and resource usage. Choosing the right one depends on your application and risk tolerance.

Recreate deployment is the simplest approach. You stop the old version, then start the new version. There is downtime during the switch. This works for development environments or applications where brief downtime is acceptable, but it is not suitable for production systems requiring high availability.

Rolling deployment updates instances gradually. If you have ten servers, you might update two at a time. Traffic shifts to updated instances as they become healthy. This minimizes downtime and uses no extra resources. However, during the rollout, both versions run simultaneously, which can cause issues if they are incompatible.

Blue-green deployment maintains two identical production environments, called blue and green. One serves live traffic while the other is idle. You deploy the new version to the idle environment, test it, then switch traffic by updating the load balancer. Rollback is instant because you just switch back. The downside is that it requires double the infrastructure.

Canary deployment releases changes to a small subset of users first. You might send five percent of traffic to the new version. If metrics look good, you gradually increase to twenty-five, fifty, then one hundred percent. This limits the blast radius of problems. If something goes wrong, only a small percentage of users are affected.

A/B testing is similar to canary but focuses on user experience rather than stability. Different user segments see different versions to measure feature impact. This is often managed by feature flags rather than deployment infrastructure.

Feature flags are not a deployment strategy per se, but they complement all strategies. You deploy code with new features disabled, then enable them for specific users or percentages. This separates deployment from release and allows instant rollback without redeploying.

For most teams starting out, rolling deployments offer a good balance. As you mature, blue-green provides safer rollbacks. Canary deployments are valuable for high-traffic applications where you want to validate changes with real users before full rollout.