DBS-C01 Deployment and Migration Practice Question
A company is running a production PostgreSQL database on an EC2 instance (db.m5.xlarge) with 500 GB of gp2 EBS storage. The database is used by a customer-facing application that requires low latency. The company plans to migrate this database to Amazon RDS for PostgreSQL with minimal downtime. The current database has a high write load with frequent updates and deletes, and the table sizes are growing. The company also wants to enable Multi-AZ for high availability and use read replicas for reporting workloads. During migration planning, they discover that the source database has several large unlogged tables and uses custom PostgreSQL extensions that are not available in RDS. Which migration strategy should the company use to minimize downtime and meet all requirements?
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, convert unlogged tables to logged tables, and migrate custom extensions using AWS SCT.
AWS DMS with ongoing replication allows near-zero downtime by continuously replicating changes from the source to the target RDS instance. DMS can handle unlogged tables by converting them to logged tables during migration, as DMS requires logical replication which relies on write-ahead logs. AWS SCT can help assess and convert custom PostgreSQL extensions to RDS-compatible equivalents or suggest alternatives. Option B (pg_dump/pg_restore) is an offline approach that would cause significant downtime, which does not meet the minimal downtime requirement. Option C (copy to S3 then restore) is not a supported migration method for PostgreSQL to RDS. Option D (streaming replication) is not feasible because RDS does not accept direct streaming replication from an external source, and unlogged tables cannot be replicated via streaming. Therefore, A is the best strategy.
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 DMS with ongoing replication, convert unlogged tables to logged tables, and migrate custom extensions using AWS SCT.
Why this is correct
DMS can handle unlogged tables by replicating data as regular tables, and SCT can suggest alternatives for unsupported extensions.
- ✗
Use pg_dump to export the database and pg_restore to import into RDS, then set up read replicas.
Why it's wrong here
This is an offline method and would cause significant downtime for a production database.
- ✗
Copy the database files to Amazon S3, then use the rdsadmin.rdsadmin_restore_from_s3 procedure to restore to RDS.
Why it's wrong here
RDS for PostgreSQL does not support restoring from S3.
- ✗
Set up PostgreSQL streaming replication from the EC2 instance to an RDS read replica, then promote the replica.
Why it's wrong here
Streaming replication requires logical replication, and unlogged tables are not replicated.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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