# Canary release

> Releasing a new version to a small slice of users first, and widening only if it behaves.

- Level: Intermediate
- Topics: Cloud
- URL: https://tidbit.legios.com.ar/canary-release/
- In Spanish: [Canary release](https://tidbit.legios.com.ar/es/canary-release/)

A **canary release** is a way to put a new version of software into production gradually. Instead of switching every user at once, you send a small share of the traffic, say 1% or 5%, to the new version while everyone else stays on the current one. Then you watch: error rates, response times, sign-ups, whatever tells you the system is healthy.

If the numbers look as good as the old version's, you widen the slice step by step, for example to 25%, then 50%, then everyone. If something goes wrong, you send all traffic back to the old version, and only a small group of users ever saw the problem. Many teams automate the whole loop: a tool shifts traffic on a schedule and rolls back on its own if a metric crosses a threshold. On AWS, CodeDeploy and Lambda can shift traffic this way; on Kubernetes, tools like Argo Rollouts and Flagger do it.

The name comes from the canaries miners once carried underground: the bird reacted to toxic gas before the people did, giving them time to get out. Compared with a blue-green deployment, which flips all traffic from one full environment to another, a canary limits how many people a bad release can hurt. The price is more complexity: two versions run at once, so they must be compatible with the same data, and you need good monitoring to know whether the canary is fine.

## An analogy

A restaurant testing a new dish on a few tables before putting it on the menu. If those diners love it, it goes out to everyone; if they send it back, only a few tables noticed.

## Keep in mind

- A small share of real traffic goes to the new version first.
- Metrics decide whether to widen the rollout or roll back.
- A bad release only reaches a small group of users.
- Both versions run at once, so they must work with the same data.

## Go deeper

- [Canary release (Martin Fowler)](https://martinfowler.com/bliki/CanaryRelease.html)
- [Canarying releases (Google SRE workbook)](https://sre.google/workbook/canarying-releases/)

## Related terms

- [AWS Lambda](https://tidbit.legios.com.ar/aws-lambda/): Run a piece of code only when something happens, with no server to manage.
- [Kubernetes](https://tidbit.legios.com.ar/kubernetes/): The system that runs and babysits containers across many machines.
- [Blue-green deployment](https://tidbit.legios.com.ar/blue-green-deployment/): Releasing a new version next to the old one and switching traffic over at once.
- [Rollback](https://tidbit.legios.com.ar/rollback/): Going back to the last version that worked when a new one causes problems.