DVA-C02 Deployment Practice Question
Which THREE factors should a developer consider when choosing between a blue/green deployment and a rolling deployment for an Amazon ECS service?
⚠ Common exam trap
Candidates often assume rolling deployments always require manual rollback (Option A) when in fact ECS supports automatic rollback via the service's 'deployment circuit breaker' feature, and they may overlook the cost implications of running dual environments in blue/green deployments (Option C).
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
✓
Rolling deployments update a subset of tasks at a time, which may cause slower rollback
Rolling deployments in Amazon ECS update a subset of tasks at a time, which means if a rollback is needed, the deployment must reverse the updates incrementally, potentially taking longer than a blue/green deployment where traffic can be switched back instantly. This slower rollback is a key trade-off when choosing between the two strategies.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Rolling deployments require manual intervention to rollback
Why it's wrong here
Rolling deployments, while updating instances in phases, do not inherently demand manual intervention for rollback. Modern deployment tools and CI/CD pipelines can be configured to automatically detect deployment failures or performance degradation and initiate an automated rollback to the previous stable version. This automation significantly reduces operational overhead and recovery time, making the statement incorrect.
- ✓
Rolling deployments update a subset of tasks at a time, which may cause slower rollback
Why this is correct
Rolling deployments operate by gradually replacing a small subset of old application instances with new ones until all are updated. This phased approach means that if a critical issue is discovered, the rollback process must also proceed in stages, replacing the faulty new instances with the previous stable version across the entire fleet. Consequently, the time required to fully revert to a stable state can be considerably longer compared to other strategies, making this a valid consideration.
- ✗
Blue/green deployments are always cheaper than rolling deployments
Why it's wrong here
Blue/green deployments typically involve provisioning and running two full, identical environments (the "blue" old version and the "green" new version) simultaneously for a period. This duplication of infrastructure, even if temporary, inherently incurs higher resource costs compared to a rolling deployment, which reuses existing infrastructure by replacing instances incrementally. Therefore, stating they are "always cheaper" is incorrect, as the cost overhead for duplicate resources is a significant factor.
- ✓
Blue/green deployments require running two versions of the application simultaneously
Why this is correct
Blue/green deployments fundamentally rely on maintaining two distinct, fully operational environments: one running the current stable application version (blue) and another running the new version (green). This parallel operation allows for thorough testing of the new version in a production-like setting before traffic is switched. The ability to instantly revert traffic to the blue environment is a direct benefit of having both versions active concurrently, validating this requirement.
- ✓
Blue/green deployments provide instant rollback by switching traffic back to the old environment
Why this is correct
A primary advantage of blue/green deployments is the near-instantaneous rollback capability. If issues arise with the newly deployed "green" environment after traffic has been switched, developers can simply redirect all user traffic back to the previously stable "blue" environment. This traffic routing change is typically a quick DNS or load balancer configuration update, ensuring minimal downtime and immediate restoration of service, making the rollback effectively instant.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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