What is bluegreen?

Blue‑green deployment is a technique for releasing new versions of software where you keep two identical production environments-one called “blue” and the other “green.” At any time, only one of them serves live traffic. When a new version is ready, you deploy it to the idle environment, test it, and then switch all users over to that environment. The old environment stays intact as a backup in case you need to roll back.

Let's break it down

  • Two environments: Blue and green are exact copies of your app, database, and configuration.
  • Current live environment: Only one (say blue) handles user requests.
  • Deploy to idle: You install the new code on the green environment while blue keeps running.
  • Test: Run automated and manual checks on green without affecting users.
  • Switch traffic: Update the load balancer or DNS so all traffic points to green.
  • Rollback: If something goes wrong, point traffic back to blue instantly.

Why does it matter?

It gives you a safe way to release changes without downtime. Users don’t see errors because the switch happens in seconds, and if the new version has a problem you can revert instantly. This improves reliability, user confidence, and makes it easier to meet “zero‑downtime” service level agreements.

Where is it used?

  • Web applications and SaaS platforms that need high availability.
  • Mobile backend services that must stay online during updates.
  • Cloud environments (AWS Elastic Beanstalk, Azure App Service, Google Cloud Run) that provide built‑in blue‑green features.
  • Continuous delivery pipelines that automate the switch as part of CI/CD.

Good things about it

  • Near‑zero downtime for users.
  • Instant rollback to a known good state.
  • Clear separation between old and new code, reducing deployment risk.
  • Easy to test the new version in a production‑like setting before going live.
  • Works well with automated CI/CD tools and cloud load balancers.

Not-so-good things

  • Requires twice the infrastructure, which can increase cost.
  • Managing data migrations can be tricky; both environments must stay in sync.
  • More complex setup and monitoring compared to simple in‑place deployments.
  • If the switch is not atomic (e.g., DNS propagation delays), a short period of mixed traffic can occur.
  • Not ideal for small projects where the overhead outweighs the benefits.