Blue-green deployment strategy explained

What is blue-green deployment?

Blue-green deployment is an application deployment strategy where old and new releases of an application run in parallel on two identical production environments. For example, the older version runs in the blue environment, while testing for the new release happens in the green environment. Once tests are complete, a router or load balancer gradually re-routes requests to the green environment. Developers then run smoke tests before switching traffic permanently to the green environment.

This approach uses two similar production environments (blue and green) to release software updates.

• Blue environment: The current production version of the application 

• Green environment: The new version of the application that is being tested

How does blue-green deployment work?

Here's how blue-green deployment works:

1. Deploy

The new version of the application is deployed to the green environment 

2. Test

The new version is tested in the green environment to ensure it meets all performance and security requirements 

3. Switch

Once the new version is stable, traffic is switched from the blue environment to the green environment 

4. Rollback

If any problems are identified, traffic can be rolled back to the blue environment

When is blue-green deployment effective?

Blue-green deployment is particularly effective when used in the following scenarios:

• Both environments are identical and isolated.

• There should be a provision for a router or Load Balancer.

• The system should work with Continuous Update.

The importance of blue-green deployment for DevOps processes

A key requirement for an efficient DevOps pipeline is deploying code to end users efficiently. Continuous deployment of code changes helps release software fast, but can also push bugs and vulnerabilities that are missed by automated checks. Depending on the organization, responsibility for the deployment of code falls to the developers themselves, or an operations team that deploys build artifacts from the CI/CD pipeline.

In either case, teams need a way to quickly test new versions of applications in a sandbox environment, deploy them to users, and then roll back to earlier versions if any issues are discovered in production. The cut-over to the new release requires careful consideration. Modern development teams frequently operate under a “release early and release often” philosophy, which is not compatible with more complex releases that require scheduling downtime during off-peak periods. The cut-over period needs to happen quickly to minimize downtime.

The basic idea behind blue-green deployments is to set up two identical production environments, one for the previous version, and one for staging tests of the new version. The two environments can be different physical devices, different virtual machines, or an operating environment with separate IP addresses for each environment.

What are the benefits of Blue Green deployments?

• Instant rollbacks. The blue-green approach allows for better detection of bugs due to the nearly identical nature of the staging and production environments. In case users find any issues with the new application running in the green environment, developers can instantly redirect requests to the older version running in the blue environment. This allows for instant rollbacks with no downtime for users.

• Seamless upgrades. Blue-green deployments automate the period between when software is “written” and when it’s live in production. In the initial upgrade, the green environment is used for testing, then serves as the production environment for the new version. The blue environment stays live for a period of time in case there is a need for rollbacks, then it’s deactivated and used for staging tests during the next rollout.

• No downtime. As soon as developers are ready they can move new code into production during a period of regular use. There is no need to wait for slow times like late nights or weekends, and no need to schedule downtime. A side benefit is the staging environment can be used to test disaster recovery or as a backup.

Disadvantages of Blue-green deployment

In some cases, the Blue-green approach might involve risks that make deployment more prone to failure and breakdown.

• Database Synchronization: Managing schema changes can be challenging. With Blue-green deployment, database and data changes must be synchronized across both the Blue and Green environments. Lack of synchronization can lead to inconsistencies.

• QA/UAT Failure Detection: In large infrastructures, it is possible that QA testing in non-production environments might miss certain errors or bugs, leading to potential issues undetected before deployment.

• Dashboard Requirement: Since this method involves maintaining two production environments with different code versions, monitoring insights on package and code status during deployment is essential for effective control and triggering actions as needed.

• Cost Implications: Blue-Green Deployment requires two parallel environments, effectively doubling production environment costs for both operation and maintenance.

Blue-green deployment and application load balancing 

Blue-green deployments require careful implementation to ensure users experience minimal impacts during cutover. One way to handle cutover is with a DNS record exchange, but this introduces limits because DNS propagation is not immediate.

Another approach is using application load balancing to slowly route traffic to the green environment, which allows for fine-tuned control of users. Load balancers can redirect traffic in case of errors in the green environment, and can be programmed to wait for a fixed duration before deactivating users or terminating users’ sessions in the blue environment.

Overall, this leads to a more seamless upgrade and fewer disruptions than forcing users to exit sessions before rerouting traffic. Load balancing may slow the process or fail for a small number of users, but most users don’t notice any downtime or differences.

Other deployment strategies

• Blue-green deployment: Blue-green deployment ensures high availability and allows easy rollback if critical bugs are discovered. It involves running two parallel environments, with one live and the other on standby, effectively minimizing downtime for the application.

• A/B deployment: Similar to Blue-Green Deployment, A/B Deployment routes a small portion of traffic to a separate server or environment. This technique is often used to assess feature utilization and gather user feedback on a new version.

• Canary deployment: Canary deployment gradually releases new features to a subset of users by assigning specific servers to different user groups. This approach is valuable for deploying features incrementally and collecting feedback throughout the release. Rolling Deployment: Rolling Deployment involves sequentially replacing servers running the old version of the application with servers running the new version. This method allows for easier pausing of the deployment if needed.

How are blue-green deployments different from canary deployments?

Unlike blue-green deployments, canary deployments do not require separate environments for testing and production. DevOps or operations teams deploy the change to a small group of users (the “canary”), test the release, and then decide whether to deploy the release to the entire user base.

Since they don’t use separate environments, canary deployments only require a small bit of extra infrastructure. They can be set up using a spare node or server, only what’s needed to support a small portion of the production environment and a small amount of traffic.

Blue-green deployments using infrastructure as code (IAC)

Blue-green deployments are a powerful technique for quickly releasing software while minimizing technological and business risks. They also require careful consideration of security. The complex architecture of applications and the environments they are deployed in, using web servers, containers, and microservices, and the use of tools for automating builds, tests, and deployments in the CI/CD pipeline, present the potential for misconfigurations, insecure environments, and surprises after cutover.

Traditional application security falls short when it comes to protecting IaC infrastructure. It focuses on the post-production application, which means bugs and vulnerabilities can end up affecting end users. Security teams operate separately from developers, which means that on the occasion security teams uncover issues, they rely on the development team for fixes, creating a bottleneck for delivery, and mismatched priorities for developers and security professionals. Furthermore, security operates as an external function of the development process rather than as an integrated part of the CI/CD pipeline.

Blue-green deployment and IaC Tools

Fortunately, there is a solution. Snyk Infrastructure as Code seamlessly integrates with the CI/CD pipeline to secure configurations before they go into production. It’s built with a developer-first focus, allowing automatic in-line code fixes. Snyk IaC includes automated tests for Terraform files and plans, AWS CloudFormation, Kubernetes configurations, Azure Resource Manager (ARM). Development teams can run IaC scans throughout CI/CD pipelines, to detect and fix configuration issues early. Drift testing with DriftCTL also detects post-deployment changes to infrastructure by people and tools outside of the regular flow. This brings ownership for build, test, and deployment security to developers, enabling DevSecOps principles using IaC tools for blue-green deployments.