Database Migration to RDS with Minimal Downtime
A data engineer is migrating an on-premises PostgreSQL database to Amazon RDS for PostgreSQL. The database is 2 TB in size and has a tight migration window. Which migration approach minimizes downtime?
Quick Answer
The answer is AWS DMS with ongoing replication because it enables a database migration to RDS with minimal downtime by continuously capturing and applying changes from the source PostgreSQL database to the target RDS instance after the initial full load. This approach leverages Change Data Capture (CDC) to keep both databases synchronized, allowing you to cut over to RDS in seconds rather than hours. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of migration strategies for large datasets under tight windows—a common trap is choosing a full dump and restore, which forces extended downtime for a 2 TB database. Remember that DMS with ongoing replication is the only option that decouples the bulk transfer from the final switchover. Memory tip: think “DMS = Data Minimizes Stoppage” to recall that ongoing replication keeps the source live until you’re ready to flip the switch.
⚠ Common exam trap
Many candidates confuse the concept of a read replica (which is an AWS-internal feature for RDS instances) with a migration tool, and mistakenly think they can replicate from an on-premises database to an RDS read replica, which is not supported.
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 DMS with ongoing replication to capture changes during migration.
AWS DMS with ongoing replication (change data capture, CDC) allows you to perform a full load of the existing data and then continuously replicate incremental changes from the source PostgreSQL database to the target RDS for PostgreSQL. This minimizes downtime because you can keep the source database fully operational during the migration and only switch applications over after the target is fully synchronized, resulting in a very short cutover window.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use AWS Database Migration Service (DMS) with full load only.
Why it's wrong here
Full load only still causes downtime for changes during migration.
- ✗
Use pg_dump to export the database and pg_restore to import into RDS.
Why it's wrong here
Full dump/restore requires application downtime.
- ✗
Create a read replica in RDS and promote it when ready.
Why it's wrong here
RDS for PostgreSQL read replica requires source to be RDS.
- ✓
Use AWS DMS with ongoing replication to capture changes during migration.
Why this is correct
Ongoing replication syncs changes until cutover, minimizing downtime.
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Same concept, more angles
3 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 data engineer needs to migrate an on-premises PostgreSQL database to Amazon RDS for PostgreSQL. The database is 2 TB and has a continuous stream of write operations. The migration should minimize downtime. Which AWS service should be used?
medium- A.AWS DataSync
- ✓ B.AWS Database Migration Service (DMS)
- C.AWS Snowball Edge
- D.AWS Glue
Why B: AWS Database Migration Service (DMS) is the correct choice because it supports ongoing replication (change data capture) from an on-premises PostgreSQL source to Amazon RDS for PostgreSQL, enabling a near-zero downtime migration. DMS can handle the 2 TB dataset and continuous write stream by performing a full load followed by continuous replication of changes until the cutover. Other services lack the ability to perform live, transactional replication with minimal interruption.
Variation 2. A data engineer is migrating an on-premises Oracle database to Amazon RDS for Oracle. The database is 5 TB in size and has a 1 Gbps network connection. The migration must be completed within 48 hours. Which service should be used?
hard- A.AWS DataSync.
- B.Amazon S3 Transfer Acceleration.
- C.AWS Snowball Edge.
- ✓ D.AWS Database Migration Service (DMS).
Why D: AWS DMS is the correct choice because it is designed for migrating databases to AWS with minimal downtime, and it can handle a 5 TB Oracle database over a 1 Gbps network within 48 hours. DMS supports ongoing replication to keep the source and target in sync, and it can use Oracle-specific features like supplemental logging and change data capture (CDC) to reduce migration time. The 1 Gbps connection provides sufficient bandwidth to transfer 5 TB in under 12 hours at full utilization, leaving ample time for setup and validation.
Variation 3. A data engineer is migrating an on-premises PostgreSQL database to Amazon RDS for PostgreSQL. The database is 2 TB in size. The engineer needs to minimize downtime. Which AWS service should be used for the migration?
easy- A.AWS Data Pipeline
- ✓ B.AWS Database Migration Service (DMS)
- C.AWS Snowball
- D.Amazon S3
Why B: AWS Database Migration Service (DMS) is the correct choice because it supports continuous replication (change data capture) from an on-premises PostgreSQL source to Amazon RDS for PostgreSQL, enabling near-zero downtime migration. DMS can handle a 2 TB database by using a large replication instance and tuning task settings, and it automatically converts the source schema to the target RDS engine.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DEA-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DEA-C01 exam.