Both solve the same problem differently
Blue-green and canary deployments are both answers to the same question: how do you release new software without taking your service offline or exposing all your users to a change that might be broken?
They solve it differently, and the right choice depends on your traffic volume, rollback requirements, and how much operational complexity your team can absorb.
Blue-green: complete environment swap
In a blue-green deployment, you maintain two identical production environments — blue (currently live) and green (the new version). You deploy your new version to green, run your smoke tests, and then switch traffic from blue to green in a single step (typically by updating a load balancer or DNS record).
The advantages are straightforward. Rollback is instant: switch traffic back to blue, which is still running your previous version, unchanged. The transition is clean — users on blue stay on blue until the switch, users on green get the new version after it. There's no period where some users see version N and others see version N+1.
The costs are also straightforward. You're running two full production environments simultaneously, which doubles your infrastructure cost for the duration of the deployment window. For large infrastructure, this is expensive even if the window is short. You also need your application to handle schema changes that are backward-compatible, since blue and green may need to share a database during the transition.
Blue-green works best when: your deployments are infrequent (weekly or monthly), your infrastructure cost during the swap is acceptable, and clean rollback is a hard requirement (common in regulated industries or where transaction integrity matters).
Canary: gradual traffic shift
In a canary deployment, you route a small percentage of traffic to the new version while the majority continues to see the old version. You watch your error rates, latency, and business metrics. If everything looks good, you gradually increase the percentage — 1% → 5% → 20% → 50% → 100%. If something looks wrong, you route all traffic back to the old version.
The advantages: you expose real user traffic to the new version before committing to it. A bug that only manifests under specific user conditions or at specific traffic volumes will appear at 5% before it affects 100% of your users. Infrastructure cost is minimal — you're running a small number of canary instances, not a full duplicate environment.
The costs: the implementation is more complex. You need traffic splitting at the load balancer or ingress layer (Kubernetes ingress controllers, AWS Application Load Balancer weighted target groups, Istio, or ArgoCD Rollouts all support this). You need metrics that you trust and alert thresholds that are calibrated. You need an automated or manual process to progress or abort the rollout. And you need to accept that during the canary window, some users are getting a different experience than others — this matters more for some applications than others.
Canary works best when: you deploy frequently (daily or multiple times per day), you have strong observability and can detect problems quickly, and your application doesn't require a clean all-or-nothing transition.
The database migration question
Both strategies share a constraint that often drives the choice: database schema changes.
A deployment that adds a new column to a table needs the database to support the new schema before the new code runs, and the old code needs to still work against the new schema during the transition. "Expand-contract" migrations — first expand the schema (add the column, keep it nullable), deploy the new code, then contract (add the NOT NULL constraint once all instances are running new code) — handle this for both strategies, but they require discipline and a two-phase deployment process.
If your team doesn't have a mature database migration practice, this complexity is the same regardless of whether you choose blue-green or canary. Solve the migration problem first; then the deployment strategy choice becomes about infrastructure cost and rollback requirements.
How we decide
When advising teams on which to use, we ask four questions:
How often do you deploy? More than once a day: canary. Weekly or less: blue-green is often simpler.
What's your rollback requirement? If you need to be able to roll back in under two minutes with certainty, blue-green's "flip the switch" is safer than canary's "drain traffic and wait."
What's your traffic volume? Canary at very low traffic (tens of requests per minute) may not give you enough signal to detect problems before you've progressed the rollout. Blue-green doesn't have this problem.
What's your observability maturity? Canary requires metrics you trust. If you're not confident in your error rate and latency measurements, canary may give you a false sense of safety. Blue-green just requires the new environment to pass a smoke test.
For teams early in their deployment maturity, blue-green with good smoke tests is often the right starting point. As observability matures and deploy frequency increases, canary becomes increasingly valuable. The two strategies are also composable: some teams run blue-green at the environment level with canary routing within each environment.
There's no universally correct answer. There is, however, usually a clearly better answer given your specific constraints — and the questions above will surface it.