Storage Cost Optimization of Amazon RDS Using Blue/Green Deployments

Amazon RDS Blue/Green Deployments provides a safe and easy way to test changes to your database before applying them to your live environment. It creates a green (staging) setup that copies your blue (production) setup and stays in sync with it. You can make updates or changes to the green environment without affecting your live production system.

Benefits of Using Blue/Green Deployments

• You will have minimal downtime during switchover.
• You can perform thorough and safe testing of changes before production rollout.
• You will have an easy rollback if any issue arises.
• There will be continuous data sync between environments.
• Lesser deployment risks.
• It helps to simplify the maintenance and configuration changes.

Steps to Optimize RDS Storage Using Blue/Green Deployment

The following is a simplified procedure to reduce allocated storage for Amazon RDS via Blue/Green deployments:

1. Log in to the AWS console. 
2. Open the RDS dashboard and select your current (Blue) RDS instance.
3. Take snapshots and all necessary backups of the RDS instance before initiating any changes. This ensures you have a restorable version in case you need to roll back.
4. Click “Create Blue/Green Deployment” from the Actions menu.
5. In the setup wizard, customize the Green environment:
6. Under “DB instance settings”, locate the storage configuration.
7. Set the reduced allocated storage size here as per your requirements(e.g., reduce from 100 GB to 50 GB).
8. You can also change instance type, networking, and other parameters if needed.
9. Launch the deployment. The Green environment will be created with your modified storage settings, and data replication will begin automatically.
10. Wait for the deployment to complete, and ensure both environments are active and synced.
11. Test the Green environment thoroughly: 
    1. Validate data consistency
    2. Run application queries and performance checks
    3. Simulate real traffic if possible
12. Once verified, click “Switchover” in the RDS Console.
13. The switch happens in less than a minute, with no data loss and minimal to zero downtime.
14. After a successful switchover, monitor your application.
15. Finally, delete the old (Blue) environment if everything looks good, to avoid unnecessary costs.

Key Considerations

When performing blue/green deployments in Amazon RDS to reduce allocated storage, it is essential to consider the following:

• If your database is allocated with more storage than the current requirement, consider reducing it. Enable storage autoscaling to allow it to grow automatically when needed.
• Ensure to align the read replica storage with your newly optimized primary DB storage for better savings.
• Avoid allowing write operations on the Green environment unless it's absolutely required. Writing to it can cause replication conflicts and unexpected behavior during switchover.
• Once you've allocated storage for an RDS instance, you can’t reduce it later, so plan the size carefully at the start.
• If you're using storage autoscaling, it's best to start with a lower initial size as per your minimum requirements, then enable autoscaling to handle growth when needed.
• Storage optimization can take a few hours, and you won’t be able to make additional storage changes until the process is finished or at least six hours pass.
• Try to schedule the switchover during off-peak hours to avoid any potential disruption to your users.
• You can configure a switchover timeout between 30 seconds and 1 hour. If it exceeds the time limit, the operation cancels automatically with no changes made.
• Always check replication health and lag between the Blue and Green environments before initiating a switchover. A healthy sync ensures minimal downtime and a smooth cutover.
• If your DB uses IAM roles, remember they won’t automatically transfer to the Green environment. You’ll need to manually attach them after the switchover.

Limitations of Blue/Green Deployments

When planning a blue/green deployment in Amazon RDS, be aware of the following restrictions:

• AWS Secrets Manager doesn’t support managing master passwords during Blue/Green deployments.
• If is Dedicated Log Volume (DLV) is enabled in your Blue instance, it must also be enabled for all related instances, including replicas.
• Make sure the Event_Scheduler is turned off in the Green environment to prevent unexpected jobs or data changes during deployment.
• You can’t switch between encrypted and unencrypted databases as part of a Blue/Green deployment.
• You can’t downgrade the database engine version; the Green environment must use the same or newer database engine version than the Blue one.
• Cross-account deployments are not supported, so both the Blue and Green environments must exist in the same AWS account. 

An Ending Note

It's strongly recommended to perform testing and a thorough assessment in a staging or non-production environment before proceeding with implementation in the production environment.

Before you begin, check for any engine-specific requirements—steps may vary based on whether you're using MySQL, PostgreSQL, or another supported engine. Please refer to the official AWS documentation and check the prerequisites accordingly for your specific engine version.