What is Blue-Green deployment?

Blue-Green deployment is a release strategy for new features with minimal downtime, based on maintaining two identical environments: "blue" (current, live version) and "green" (new version).

Algorithm:

1. There is an active "blue" environment serving all traffic.
2. The new application version is deployed in a fully identical but inactive "green" environment.
3. After successful testing of the "green" environment, traffic is switched to it.
4. The "blue" environment is kept for quick rollback or can be used for subsequent deployments.

Key advantages:

• Minimal downtime: Traffic switching is almost instantaneous.
• Easy rollback: In case of issues with the new version, traffic can be easily redirected back to the "blue" environment.
• Lower risk: The new version is tested in an isolated environment before switching traffic.

Disadvantages:

• Double resources: Resources are required to maintain two full environments.
• State management: Managing application state can be challenging if it uses a database with constant changes.

Example of traffic switching using a load balancer:

// Simplified load balancer configuration
{
  "listeners": [
    {
      "port": 80,
      "protocol": "HTTP",
      "default_actions": [
        {
          "type": "forward",
          "target_group_arn": "arn:aws:elasticloadbalancing:..." // ARN of the "blue" environment target group
        }
      ]
    }
  ]
}

# Command to switch traffic to the "green" environment
# (example for AWS CLI, assuming the ARN of the new target group is available)
aws elbv2 modify-listener --listener-arn "arn:aws:elasticloadbalancing:..." --default-actions Type=forward,TargetGroupArn="arn:aws:elasticloadbalancing:..." // ARN of the "green" environment target group