How to Perform Amazon RDS Upgrades With Near-Zero Downtime

Amazon RDS, or Amazon Web Services Relational Database Service, is a web service that helps simplify the setup, operation, and scaling of a relational database in the cloud. It not only automates time-consuming administrative tasks but also enables the focus to remain on applications to provide fast performance, high availability, security, and compatibility.

However, like all technologies, RDS instances must also be periodically upgraded. Unfortunately, there is always a risk of downtime during these upgrades, and as we all know, downtime equates to tangible loss for any business. Herein lies the challenge: how to effectively upgrade Amazon RDS instances without encountering substantial downtime?

This guide is designed to provide you with the essential roadmap and strategies for performing Amazon RDS upgrades with minimal to near-zero downtime. By understanding update dynamics, utilizing in-built tools, implementing best practices, and staying aware of the latest AWS developments (like the amazing Amazon RDS Blue/Green deployments), you can minimize interruptions and ensure smooth transitions during your database upgrades.

Amazon RDS supports DB engines, including MySQL, PostgreSQL, MariaDB, Oracle, SQL Server, and of course, their own Amazon Aurora in both their MySQL and PostgreSQL compatibility versions. This post focuses primarily on the standard RDS engines and does not cover Aurora, as it has special characteristics that we will cover in a separate blog post.

So, let's start our path down this crucial aspect of Amazon RDS management - reducing downtime during upgrades.

How Long Does it Take to Upgrade an RDS Instance?

When planning an Amazon RDS upgrade, understanding the time involved serves as a critical planning factor. The time largely depends on your database sizing, with larger databases taking longer to upgrade than smaller ones. Generally, upgrades range from a few minutes to several hours, with downtime typically occurring during the "modifying" and "upgrading" stages of the process.

So, you may ask, “How can I reduce the downtime involved?” This is where the Multi-AZ and Blue/Green deployments come in. They help to minimize downtime during modifications, updates to DB instance class, OS, or hardware maintenance, albeit the level of availability they provide depends on the specifics of the change type.

Does RDS Minor Version Upgrade Cause Downtime?

Minor version upgrades can be manually scheduled through the RDS console or API or automatically carried out when an engine is deprecated. It should be noted that because RDS doesn’t automate rolling upgrades, the DB engine version upgrade takes place on both the primary and standby hosts simultaneously. As a result, deploying a DB engine version upgrade doesn't particularly benefit from a Multi-AZ setup.

To evaluate the scope and potential duration of impact, it's recommended to carry out the upgrade in a staging environment before the actual production environment upgrade. This gives you a projection of the potential downtime, allowing you to properly time and schedule updates to reduce impact on ongoing operations.

In situations where your RDS DB instance utilizes read replicas, ensure you upgrade all the read replicas before upgrading the source instance. This strategy helps reduce potential downtime when upgrading your database.

What is The Failover Time for RDS?

Failover time for Amazon RDS is a critical parameter that users must understand to ensure minimal business impact during database transition times such as maintenance events or instance failure. The failover period refers to the time it takes for RDS to switch from a primary DB instance to a standby replica in case of scenarios that threaten data integrity or DB Instance availability.

The Amazon RDS Multi-AZ deployments provide high availability and failover support for DB instances. In the event of a database problem, the Amazon RDS platform performs an automated failover from the primary to the standby instance, guaranteeing that your database operations continue to function relatively seamlessly.

The failover time can range from 60-120 seconds, although this may vary based on the nature of the workload, the database engine in use, and other factors. This switchover operation does occur automatically, so manual interventions are unnecessary during these maintenance events, effectively reducing error and system downtime.

However, it's worth noting that during a failover, existing connections to the DB are dropped and must be re-established by the application. To handle this efficiently, applications should have retry logic to cater to these instances.

The Essential Role of Maintenance Window in RDS Upgrades

Routine maintenance is essential to ensure the smooth functioning of your RDS instances, and hence, you must know how to manage the maintenance window for your Amazon RDS.

Understanding the Amazon RDS Maintenance Window

The maintenance window is a defined, recurring time range during which system maintenance can occur. This is when updates to the DB engine, the operating system, or any other software component in the stack are performed.

Amazon RDS offers a 30-minute maintenance window selected during DB instance creation. During this window, Amazon can perform necessary maintenance tasks such as minor and major DB Engine version upgrades.

It's crucial to remember that not every maintenance window results in downtime. If an operation can be performed without interrupting your DB instance availability or performance, AWS will schedule that operation during the maintenance window.

How to Adjust the Preferred DB Instance Maintenance Window?

Scheduling maintenance tasks at off-peak times can help minimize the impact of any potential disruption. As a result, Amazon RDS allows users to adjust their preferred maintenance window.

You can change the maintenance window for a DB instance at any time by using the RDS console, the AWS CLI 'modify-db-instance' command, or the RDS API 'ModifyDBInstance' operation. The change is immediately applied to your next maintenance event unless you decide to apply it immediately.

Automatic Minor Version Upgrades

Keeping database engine versions up-to-date improves the security and performance of your databases. With auto minor version upgrades enabled, Amazon RDS can automatically manage these updates, reducing manual oversight.

In automatic upgrades, RDS identifies and assigns a preferred minor engine when a database is running a lower version and the auto minor version feature is activated. The upgrade process includes pre-upgrade health checks, DB engine upgrade, post-upgrade checks, and finally, marking the upgrade as complete.

To enable auto minor version upgrades, you can use the RDS console or the 'modify-db-instance' command in AWS CLI. Remember, these automatic upgrades do result in downtime, whose duration depends on several factors, such as the DB engine type and database size.

To stay informed about upcoming maintenance updates, you can use the AWS CLI command - 'describe-pending-maintenance-actions'. To determine the latest minor version your database can upgrade to, use the 'describe-db-engine-versions' AWS CLI command.

For in-depth information about this feature and its settings, refer to the Amazon RDS documentation: Automatically upgrading the minor engine version

Types of Maintenance That Requires DB Instance to Be Offline

Everyone knows that when you’re making changes to an RDS DB Instance, and it’s configured on a Single-AZ, there might be changes that cause downtime. But there’s a common misconception that by enabling Multi-AZ you will be able to make any changes without downtime. In this section, we cover some of the most common changes, how Multi-AZ affects the change, and how to find if the change you want to make will cause downtime.

1. Modifying DB instance storage

Changes to allocated storage size and IOPs values or switching between storage types are online operations that usually don't include downtime. However, since these updates are simultaneously applied to primary and standby DB instances, Multi-AZ deployments don't provide additional availability benefits during these changes.

Keep in mind that downtime can occur when switching between General Purpose (SSD) and Magnetic storage types and when changing from Provisioned IOPS (SSD) to General Purpose (SSD) and vice versa.

2. Updating DB instance class

Since updating the DB instance class calls for a newly defined set of hardware, this operation is not online and, thus, involves downtime. By introducing a Multi-AZ deployment, the impact can be significantly reduced. In this scenario, modifications are first made to the standby instance, followed by a failover, and then modifications to the new standby. 

This process only sets downtime equivalent to the duration of the failover and completion of the DB engine’s crash recovery.

3. DB engine version upgrade

DB engine version upgrades can either be manually scheduled through the RDS console or the API or automatically carried out through minor version updates or engine deprecation. As simultaneous upgrades happen on primary and standby hosts, Multi-AZ deployments do not provide any added benefit.

To evaluate the duration and scope of impact, it’s recommended to test the upgrade in a staging environment ahead of the actual production upgrade. Should your RDS DB instance make use of read replicas, it’s critical to update all read replicas before the source instance.

4. Scheduled OS or hardware maintenance

A Multi-AZ deployment can considerably lower the impact of scheduled OS or hardware maintenance events. If maintenance is scheduled for only the primary host, a failover is initiated, and maintenance is performed on the new standby host. For maintenance events scheduled for the secondary host, no downtime is caused. In contrast, for cases where both primary and secondary hosts require maintenance, the standby host comes first, followed by a failover. Then, maintenance is carried out on the new secondary host.

How Do I Know if a Specific Change Will Cause Downtime?

If you want to know if a specific RDS change will cause downtime, both in cases of Single-AZ and Multi-AZ deployments, you can always refer to the AWS Documentation page: Modifying an Amazon RDS DB instance

Blue/Green Deployments: a Revolution in RDS Updates

As technologies are rapidly improving, Amazon has been keen on providing the most reliable and time-efficient methods to perform necessary database changes and updates. A key part of this is the introduction of Blue/Green deployments for RDS. This new feature automates a lot of the processes that we had to do manually in case of upgrades on highly available systems that couldn’t afford more than a few minutes of downtime at most.

What is Blue/Green Deployment?

In a blue/green deployment, the 'blue' environment signifies the current production environment, while 'green' refers to the staging environment. The staging environment is an exact copy of the production environment, kept in sync with the current production using logical replication. This allows users to change the RDS DB instances within the 'green' environment without impacting the production workloads. This means you can run the gamut of upgrades, parameter changes, or schema changes without exposing your production to risk, as it all happens within the staging environment.

Benefits of Utilizing Blue/Green Deployment for Updates

Blue/Green deployments have many benefits that make managing Amazon RDS upgrades significantly more efficient and less risky. Here are the key advantages:

• Easy creation of a production-ready stage environment: the green environment is an exact replica of your current production setup, making it ready for testing.

• Automatic replication of database changes: changes made to the data in the production environment are automatically reflected in the staging environment, keeping it consistent and up-to-date.

• Safe testing zone: the green environment lets you test all changes made without impacting the production environment, ensuring your databases continue to operate without interruption.

• Stay current with patches and system updates: blue/green deployment allows the testing of new patches and updates in the staging environment before they go live.

• Implement and test new database features: this deployment method is also useful when adopting new features offered by the database engine, such as enabling IAM authentication.

• Rapid shift into production: once tested and deemed efficient, the staging environment can be promoted to the production environment swiftly and without any need for applications to change.

Availability of Blue/Green Deployment  

Blue/green deployments are currently supported only for RDS for MariaDB and RDS for MySQL. If you want to perform a similar type of upgrade, it’s possible to write your own custom scripts for another database engine, and follow the same process that AWS has automated and offered as a service.

By using Amazon RDS Blue/Green deployments, you can effectively reduce the risk and downtime often associated with major or minor engine version upgrades, ensuring a seamless update experience. You can read more about it in the official AWS Documentation: Using Amazon RDS Blue/Green Deployments for database updates

Do You Need Help With Amazon RDS Upgrades?

By understanding the dynamics of Amazon RDS upgrades and utilizing the in-built tools like Multi-AZ and Blue/Green deployments, businesses can ensure smooth transitions with minimal disruptions during their database upgrades. The goal is to keep the focus on providing fast performance, high availability, security, and compatibility for applications, thus minimizing tangible losses that arise from downtime.

If the prospect of optimizing your AWS RDS upgrades seems daunting, or if you’re looking to enhance the efficiency and security of your database transitions, StratusGrid is here to assist. Our team of experts is adept at tailoring solutions that minimize disruptions and maximize performance.

Contact StratusGrid today, and let’s ensure your database transitions are smooth, secure, and efficient.

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