Blue-Green Deployments Explained

A blue-green deployment strategy is the perfect solution for when uptime is critical. It's a technique that minimizes system downtime and risk by running two identical production environments called blue and green. For example, the blue environment is currently live and the green instance is idle. When there's a problem in one environment, engineers can switch to the other in order to maintain uptime in the event of an emergency. 

As you prepare for an updated release of your software, deployment and testing will take place in a test environment that won't affect the live system. Once your new code is ready, you'll switch the router so all incoming requests go to the new version in the test environment instead of the live system. The new version becomes the live system, and the older version becomes idle. 

The idea behind blue-green deployments is to reduce the risk of downtime during deployment. This technique can also lessen the amount of time it takes to roll back an app if something goes wrong. Should anything unexpected happen with the new version, a business can immediately roll back to the last “green” version by switching back to the “blue” one.

If you have an application that doesn't store any data, then you can start doing zero downtime deployment. Unfortunately, most software stores data, which means that you need to think about making schema changes before doing any sort of deployment.  

With blue/green deployment, engineering teams can always ensure they have a working version of the website ready. If something goes wrong with the green version, they can switch back to the blue version and address the issue at a later date. This is ideal if an issue arises at an inconvenient time like the end of a long workday or on a Friday evening. With blue-green deployment, the issue can be resolved the following day or on a Monday morning.  

The other great benefit of this approach is that tests are performed in production. This allows developers to work with a full environment, which makes them confident the application will work as expected. If it doesn't, there's still an easy way to revert back to the old version. 

Running Safe Canary Releases

While blue/green deployment is risk-free, there is an even safer strategy; canary releases. The canary deployment strategy uses rolling deployment which involves testing your code on only a subset of user traffic before rolling it out to the entire user base. This allows DevOps teams to avoid any mistakes in production or performance issues while making changes to their codebase based on testing in a live environment.  

Using the method of canary tests, you can deploy a new feature to 10% of your visitors first to test the bugs before deploying the new update to 100% of your users. When releasing a new version of your site, it's important to have a controlled blast radius. A new release doesn't have to immediately switch 100% of your users over to the new version.