AWS DMS Minimal Downtime Migration
A company is migrating an on-premises MySQL database to Amazon RDS for MySQL. The database is 500 GB and has a 24/7 uptime requirement. The migration must minimize downtime. Which approach should be used?
Quick Answer
The correct approach is to use AWS Database Migration Service (DMS) with ongoing replication. This method minimizes downtime by first performing a full load of the 500 GB database, then continuously replicating incremental changes from the on-premises MySQL source to the Amazon RDS target using change data capture (CDC). Because the target stays synchronized in near real-time, you can cut over to RDS in seconds rather than taking the source offline for hours. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of DMS’s ongoing replication feature for zero-downtime migrations—a common trap is choosing a snapshot-based or backup-restore approach, which requires extended downtime for the final sync. Remember the key distinction: full load alone is not enough; you need CDC to keep the target current until cutover. A helpful memory tip is “DMS with CDC: sync now, cut over later.”
⚠ Common exam trap
Test-takers frequently choose mysqldump (Option C) because it is a familiar tool, but they overlook the requirement for minimal downtime and the fact that a 500 GB dump/import would take hours, violating the 24/7 uptime requirement.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use AWS Database Migration Service (DMS) with ongoing replication to migrate the data.
AWS DMS with ongoing replication (change data capture) allows you to perform a full load of the 500 GB database and then continuously replicate changes from the on-premises MySQL source to the Amazon RDS target. This minimizes downtime because you can cut over to RDS in seconds after the target is synchronized, rather than taking the source offline for an extended period.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Take a snapshot of the on-premises database, convert it to a volume, and restore to RDS.
Why it's wrong here
A snapshot-and-restore approach requires taking the source offline to guarantee consistency, causing downtime that breaches the 24/7 requirement. It is used for smaller databases where a maintenance window is acceptable and continuous availability is not required.
- ✓
Use AWS Database Migration Service (DMS) with ongoing replication to migrate the data.
Why this is correct
AWS DMS with ongoing replication performs a full load then continuously applies change data capture from the source MySQL binlog, keeping the target synchronised so cutover downtime is limited to a brief switchover rather than the whole 500 GB transfer.
- ✗
Export the database using mysqldump and import it into RDS using mysql command.
Why it's wrong here
mysqldump locks tables during export and the subsequent import takes hours for 500 GB, so downtime far exceeds the requirement. It is used for small databases or schema-only transfers where a maintenance window is tolerable.
- ✗
Create an RDS MySQL read replica from the on-premises database using native replication.
Why it's wrong here
Native MySQL replication from on-premises to RDS requires network connectivity and configuration, and RDS read replicas are created from an existing RDS instance, not an external server. It suits ongoing replication between MySQL instances, not a one-off migration.
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Same concept, more angles
5 more ways this is tested on DEA-C01
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company is migrating an on-premises MySQL database to Amazon RDS for MySQL. The database is 500 GB in size. The migration must have minimal downtime and must be completed within a week. Which AWS service should the data engineer use to perform the migration?
easy- A.Amazon S3 Transfer Acceleration.
- B.AWS Snowball Edge.
- C.AWS DataSync.
- ✓ D.AWS Database Migration Service (DMS).
Why D: AWS Database Migration Service (DMS) is the correct choice because it is specifically designed for migrating databases to AWS with minimal downtime. DMS can perform a full load of the 500 GB MySQL database and then continuously replicate ongoing changes from the on-premises source to the Amazon RDS target using change data capture (CDC), allowing the migration to complete within a week with near-zero downtime.
Variation 2. A company is migrating a MySQL database to Amazon RDS for MySQL. The database is 2 TB in size and the company can only afford minimal downtime. The migration must be secure and use AWS DMS. Which TWO configuration steps are required? (Choose TWO.)
easy- ✓ A.Create a source endpoint pointing to the on-premises MySQL database.
- ✓ B.Create a target endpoint pointing to the Amazon RDS instance.
- C.Configure SSL/TLS encryption for the DMS endpoints.
- D.Set up VPC peering between the on-premises network and the Amazon VPC.
- E.Create a DMS replication instance.
Why A: Option A is correct because AWS DMS requires a source endpoint that defines the connection details (hostname, port 3306, credentials) to the on-premises MySQL database so DMS can read the data. Option B is correct because a target endpoint pointing to the Amazon RDS for MySQL instance is mandatory for DMS to write the migrated data into the destination database. Both endpoints are essential components of any DMS migration task, and for a 2 TB database with minimal downtime, DMS uses these endpoints to perform a full load plus ongoing replication (CDC) from the source to the target. Option C is not required by the question's stated conditions—SSL/TLS is a security best practice but not a mandatory configuration step for DMS to function. Option D is not required because connectivity can be established via other means such as VPN, Direct Connect, or public endpoints, and VPC peering alone does not cover on-premises-to-VPC connectivity. Option E is not one of the two required steps in this context since the question asks specifically about endpoint configuration steps, and a replication instance, while part of DMS, is a separate resource rather than an endpoint configuration step.
Variation 3. A company is migrating its on-premises Oracle database to Amazon RDS for Oracle. The database is 2 TB in size and has a 24-hour maintenance window. The migration must have minimal downtime. Which AWS service should be used for the migration?
medium- A.Amazon RDS native backup and restore
- ✓ B.AWS Database Migration Service (DMS)
- C.Amazon S3 Transfer Acceleration
- D.AWS Snowball Edge
Why B: AWS Database Migration Service (DMS) is the correct choice because it supports heterogeneous migrations (Oracle to RDS for Oracle) with minimal downtime using ongoing replication via Oracle LogMiner or binary reader. DMS can perform a full load of the 2 TB database and then continuously replicate changes from the source to the target during the 24-hour maintenance window, allowing a final cutover with only seconds of downtime.
Variation 4. A company is migrating its on-premises PostgreSQL database to Amazon RDS for PostgreSQL. The database is 5 TB in size and supports a critical application that requires less than 30 minutes of downtime. The company has a 1 Gbps network connection to AWS. The data engineering team plans to use AWS Database Migration Service (DMS) with change data capture (CDC) to keep the target in sync. During the full load phase, DMS is taking longer than expected, and the team is concerned about meeting the downtime window. Which action should the team take to speed up the full load?
medium- A.Increase the compute capacity of the target RDS instance.
- B.Enable DMS validation to ensure data integrity.
- C.Use AWS Snowball Edge to transfer the data offline.
- ✓ D.Create multiple DMS tasks to load different tables in parallel.
Why D: Creating multiple DMS tasks to load different tables in parallel (Option D) is the correct action because DMS performs full load sequentially within a single task. By splitting tables across multiple tasks, the team can parallelize the data transfer, utilizing the 1 Gbps network more efficiently and reducing the overall full load time to meet the 30-minute downtime window.
Variation 5. A company is migrating an on-premises MongoDB database to Amazon DocumentDB. The migration must have minimal downtime. Which service should be used to perform the migration?
medium- A.AWS Glue
- B.AWS DataSync
- ✓ C.AWS Database Migration Service (DMS)
- D.Amazon S3 Transfer Acceleration
Why C: AWS Database Migration Service (DMS) is the correct choice because it supports continuous replication from MongoDB to Amazon DocumentDB using change data capture (CDC), enabling near-zero downtime migrations. DMS can perform a full load of existing data and then apply ongoing changes from the source MongoDB oplog, keeping the target DocumentDB synchronized until the cutover.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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