mediumMultiple Select
Google PCA Practice Question: Migrate a large on-premises relational database…
A company wants to migrate a large on-premises relational database to Cloud SQL for PostgreSQL with minimal downtime. They need to ensure data consistency during the migration. Which THREE steps should they take?
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
✓
Set up a VPN or Cloud Interconnect between on-premises and GCP
Option A is correct because a reliable, low-latency private network path via Cloud VPN or Cloud Interconnect is required for the initial bulk data transfer and for Database Migration Service's continuous replication to keep the on-premises source and Cloud SQL in sync with minimal downtime. Option D is correct because Database Migration Service (DMS) for PostgreSQL supports continuous replication (change data capture) from the on-premises source to Cloud SQL, which is the key mechanism for minimizing downtime and maintaining data consistency until cutover. Option E is correct because performing an initial export/import (for example, using pg_dump and pg_restore) seeds Cloud SQL with the existing dataset before continuous replication begins, so DMS only has to apply ongoing changes rather than the entire database. Option B is not appropriate because Cloud SQL read replicas replicate from a Cloud SQL primary, not from an external on-premises PostgreSQL source, so they cannot serve as the migration replication mechanism. Option C is not appropriate because switching traffic immediately after the initial import would cause data written to the source during and after the import to be lost, breaking consistency; traffic should only be cut over after replication has caught up and the systems are synchronized.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Set up a VPN or Cloud Interconnect between on-premises and GCP
Why this is correct
A VPN or Cloud Interconnect provides the private, stable network path required for continuous replication traffic between the on-premises source and Google Cloud. Without it, Database Migration Service cannot stream changes reliably, undermining the minimal-downtime and consistency goals.
- ✗
Create a read replica of the source database in Cloud SQL
Why it's wrong here
A Cloud SQL read replica replicates from a Cloud SQL primary, not from an external on-premises server. Continuous replication from on-premises requires Database Migration Service, which streams changes and keeps the target consistent until cutover.
- ✗
Switch traffic to Cloud SQL immediately after the initial import
Why it's wrong here
Switching traffic before the replica has caught up leaves transactions written to the source after the initial import missing, breaking consistency. Cutover belongs at the end of the migration, once replication lag reaches zero and the source is quiesced.
- ✓
Use Database Migration Service to start continuous replication from the source
Why this is correct
Database Migration Service performs continuous replication of ongoing changes from the on-premises source into Cloud SQL, keeping the target synchronised until cutover. This directly satisfies the minimal-downtime and data-consistency requirements, since only a brief final catch-up is needed.
- ✓
Perform an initial export of the source database and import into Cloud SQL
Why this is correct
Exporting and importing establishes the initial baseline copy of the source database in Cloud SQL before replication begins. Continuous replication then applies only subsequent changes, so this seeding step is necessary to reach consistency with minimal overall downtime.
Go deeper
Related to this question
Learn chapter
IAM Policies, Service Accounts, and Auditing
Key term
Latency
Latency is the time delay between a request being sent over a network and the response being received, often measured in milliseconds.
Key term
Cloud VPN
A Cloud VPN is a service that securely connects your private network to a cloud provider's network over the public internet using encryption and authentication.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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