Minimal Downtime PostgreSQL Migration Using AWS DMS with CDC
A company is migrating a 500 GB on-premises PostgreSQL database to Amazon RDS for PostgreSQL. The migration must have minimal downtime and support ongoing replication after the initial load. Which AWS service should be used?
Quick Answer
The answer is AWS Database Migration Service (DMS) with ongoing replication, because this scenario requires minimal downtime PostgreSQL migration to RDS using DMS CDC. DMS captures ongoing changes from the source database’s transaction logs—specifically PostgreSQL’s Write-Ahead Log (WAL)—and continuously applies them to the target RDS instance, allowing the initial 500 GB load to complete while keeping both databases synchronized. This enables a near-zero-duration cutover, as you only need to stop writes on the source and promote the target. On the AWS Certified Database Specialty DBS-C01 exam, this question tests your understanding of change data capture (CDC) as a core requirement for low-downtime migrations; a common trap is choosing a full-load-only service, which cannot support ongoing replication and forces extended downtime during the final sync. Remember the memory tip: “DMS with CDC = WAL for zero downtime.”
⚠ Common exam trap
Many exam-takers confuse 'full load only' with 'full load + CDC' and overlook the requirement for ongoing replication, or they mistakenly think AWS SCT handles data migration when it only handles schema conversion.
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
✓
AWS Database Migration Service (DMS) with ongoing replication
AWS Database Migration Service (DMS) with ongoing replication (change data capture, CDC) is required because the scenario demands minimal downtime and continuous synchronization after the initial 500 GB load. DMS uses transaction logs (e.g., PostgreSQL WAL) to capture and apply ongoing changes, enabling a near-zero-duration cutover. Full load only (Option B) would cause downtime during the final sync and cannot support ongoing replication.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
AWS Schema Conversion Tool (SCT)
Why it's wrong here
SCT converts schema but does not handle data migration or replication.
- ✗
AWS Database Migration Service (DMS) with full load only
Why it's wrong here
Full load only causes downtime; CDC is needed for ongoing replication.
- ✓
AWS Database Migration Service (DMS) with ongoing replication
Why this is correct
DMS supports full load plus CDC for minimal downtime.
- ✗
AWS Glue
Why it's wrong here
Glue is for ETL, not live database migration with replication.
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Same concept, more angles
2 more ways this is tested on DBS-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 a 500 GB on-premises PostgreSQL database to Amazon RDS for PostgreSQL. The migration must have minimal downtime and support ongoing replication after the initial load. The network link has limited bandwidth, and the company wants to avoid costly data transfer fees. Which approach should be used?
medium- ✓ A.Use AWS DMS with ongoing replication (CDC) from the start.
- B.Use AWS Database Migration Service (DMS) with a full load only, then cut over.
- C.Use pg_dump to export the database and pg_restore to import into RDS.
- D.Use AWS Snowball Edge to transfer the database files, then load into RDS.
Why A: AWS DMS with ongoing replication (CDC) enables a full load followed by continuous change data capture, which meets the requirements of minimal downtime and ongoing replication. DMS compresses data in transit and can throttle network usage, helping to manage limited bandwidth and avoid costly data transfer fees by using the existing network link efficiently.
Variation 2. A company is migrating a 2 TB on-premises PostgreSQL database to Amazon RDS for PostgreSQL. The migration must have minimal downtime and support ongoing replication. Which AWS service should be used?
medium- ✓ A.AWS DMS
- B.AWS Snowball Edge
- C.AWS S3
- D.RDS native PostgreSQL logical replication
Why A: AWS DMS (Database Migration Service) is the correct choice because it supports both full-load migration and ongoing change data capture (CDC) replication from an on-premises PostgreSQL source to Amazon RDS for PostgreSQL, enabling minimal downtime. DMS uses logical replication slots to capture incremental changes, allowing the target database to stay synchronized during the cutover window.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DBS-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 DBS-C01 exam.