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More Than A Toggle: Using Feature Flags for Database Migrations Without Disrupting Your End User

Madison Maher


Using Feature Flags for Database Migrations

Migrations can certainly be risky and cause headaches for dev teams, but they don’t have to be so cumbersome when done right. Feature flags are a great tool for managing transitions from one infrastructure component to another. Most people associate feature flags with smaller releases and the ability to toggle features on and off, but you can also use them to aid in larger scale projects (such as infrastructure migrations) for things like: maintaining data integrity, testing the new system, and maintaining an optimal user experience in the process.

In this article, we’ll explore how TechWave, a leading cloud-based analytics provider, leveraged feature flags to ensure data integrity, conduct thorough testing, and provide users with an uninterrupted experience during their DynamoDB migration.

TechWave's Challenge: The DynamoDB Migration

When TechWave’s CTO announced an upcoming migration to DynamoDB, their engineering team initially pushed back. Their devs couldn’t understand why their CTO would want to undergo a migration when it poses risk to their data and user experience. And let’s face it, no one ever likes the idea of a DB migration. 

But the migration was necessary to handle growing user data volumes and provide uninterrupted service, so the cost benefit to doing it was greater in the long run. And with feature flags in place, the migration was less daunting than it originally seemed. Here’s how they used them:

Step 1: Ensuring Data Integrity

As a data-analytics provider, preserving data integrity was non-negotiable during the migration, and a top priority for TechWave’s team.  To ensure a seamless transfer from one database to the other, TechWave created a system to bulk transfer the data, and ensure that data was synchronized between the two databases during the migration.

By strategically using feature flags to control data flow, TechWave ensured that data integrity was maintained throughout the migration process. This allowed them to compare data discrepancies in real-time and take corrective actions, ensuring a smooth and secure transition.

Step 2: Thorough Testing

TechWave also understood that robust testing was essential to minimize the risk of issues arising during migration. 

The team used feature flags to create test environments parallel to their existing database setup. For example, they used feature flags to switch between the old database and DynamoDB seamlessly. This flexibility enabled them to run various test scenarios, such as load testing, data validation, and performance testing, while ensuring minimal disruption to their production environment – the one that impacted their end users.

They were also able to test in production by routing all traffic to both databases at the same time. This allowed them to compare the responses from each database call, logging any differences for validation by the team and monitoring system performance.

Step 3: Optimizing User Experience

Feature flags helped them fine-tune the user journey and minimize disruptions during the migration.

By using feature flags to control user access to the new DynamoDB environment, TechWave ensured that users experienced a seamless transition. For example, they gradually introduced user groups to DynamoDB by enabling the feature flag for a small percentage of users. This allowed them to closely monitor the user experience for those on DynamoDB, gather feedback, and make real-time adjustments, all while ensuring that the majority of users continued to use the old database without interruptions.

The use of feature flags also required that TechWave also think through ways to reduce the risk of the data migration. Implementing the data synchronization system for the feature flags ensured that if there were a problem with the migration, the entire system could be rolled back without impact upon the users.

Step 4: Feature Flags for a Gradual Transition to the New DB 

TechWave opted for a gradual transition approach, gradually increasing the percentage of users directed to DynamoDB. Feature flags allowed for precise control over this transition.

They started by enabling the DynamoDB feature flag for 5% of their user base, closely monitoring system performance and user feedback. As they gained confidence in DynamoDB's stability, they incrementally increased the percentage. This gradual transition ensured a smooth migration without overloading the new system or causing disruptions. 

Step 5: The Final Stage: Seamless Completion

As the DynamoDB migration reached its final stages and the new database system proved its mettle, TechWave used feature flags to complete the transition.

In the final phase of the migration, TechWave used feature flags to direct all users to DynamoDB seamlessly. With feature flags, they could instantly complete the migration process without requiring users to make any changes or experience interruptions. This ensured a smooth and uninterrupted user experience throughout the migration.


TechWave's successful DynamoDB migration, powered by feature flags, demonstrates how these tools can ensure data integrity, enable thorough testing, and maintain an optimal user experience during complex database migrations. In the world of SaaS, where data is critical, user experience is paramount, and testing is rigorous, feature flags prove to be indispensable allies. They help in navigating the intricate landscape of database migrations and ensure a smooth transition without sacrificing data integrity or user satisfaction. Remember, feature flags are more than just toggles; they are your key to a seamless, disruption-free database migration.

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Written By

Madison Maher