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Blue/Green deployment is a technique used in automated deployment of applications, databases and services. Its main goal is to minimize the downtime and risks of an application by running two identical environment instances, one called Blue and the other one called Green.
Let’s say you have a production environment called Blue, running for instance an e-commerce application. Your customers are routed to this Blue instance. In parallel, you will have a “sleeping clone” of Blue, named Green. Now let’s say you have achieved a new feature and want your customers to benefit of it. Using the “Blue/Green” technique, the new code will be used in Green. Once Green is ready, you will redirect your customers to Green, and we will put Blue in “sleeping mode”. When you will add new modification you will do it on Blue this time, then on Green again, and so on.
There are many benefits to this approach:
- if Green fails to deploy there will be no downtime for your customers or users as you will not use the broken Green and stay on “Blue” until you fix your code so it can start
- if you are not happy with the changes you added in Green, you can “awake” Blue and get back to the previous version easliy by routing the traffic to it
In the Clever Cloud context
When you push your source code to the Clever Cloud git remote, Clever Cloud will automatically use the “Blue/Green” pattern to apply your changes to your production.
A new VM, let’s call it Blue is created. The deployment is successful when there’s no error in the build phase and the server answers on :8080/ with a non error code. And that’s it, you will use the new version on production within secondes.
If you push new changes, a Green VM will be created.
If the deployment succeeds, Green will be the version in production and Blue will be turned off minutes later. This way, if you are not happy with the changes you made, just go the Clever Cloud web console, select your application and in the Overview menu, click the “Start last pushed commit” button, this will “awake” Blue and reverse your changes in production within a few minutes.
If there is an error during the build phase or if the Green servers answers an error code on :8080/, we will alert you by email and Blue will remain the production server.
Next time you push code a new Green VM will be created, then a Blue one, and so on.
You also may see some deployments that you haven’t triggered in your logs. It is because Clever Cloud uses “Blue/Green” pattern to update VMs, either security patches or versions updates.