SOA-C02 Reliability and Business Continuity Practice Question
A company has a production application running on Amazon ECS with Fargate launch type. The application uses an Application Load Balancer. The SysOps administrator notices that during deployments, the application experiences a brief period of downtime. Which combination of actions should the administrator take to achieve zero-downtime deployments?
⚠ Common exam trap
Watch out — candidates often confuse the minimum healthy percent and maximum percent values, mistakenly thinking that allowing all tasks to be replaced at once (0/100) is acceptable, or that blue/green deployments inherently guarantee zero downtime without proper configuration.
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
✓
Configure the ECS service to use a rolling update with a minimum healthy percent of 100 and a maximum percent of 200.
Setting the minimum healthy percent to 100 and maximum percent to 200 ensures that during a rolling update, the ECS service first launches new tasks (up to 200% of the desired count) before terminating any old tasks. This guarantees that the ALB always has a sufficient number of healthy targets to serve traffic, eliminating downtime. The Application Load Balancer distributes traffic between old and new tasks during the transition, achieving zero-downtime deployments.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure the ECS service to use a rolling update with a minimum healthy percent of 0 and a maximum percent of 100.
Why it's wrong here
This configuration allows ECS to terminate all existing tasks before starting replacements, because the minimum healthy percent of 0 permits the service to drop to zero running tasks and the maximum of 100 prevents any additional capacity from being created first. As a result, during a deployment there is a period with no available tasks to serve traffic, causing downtime. This violates the requirement for zero downtime.
- ✗
Increase the deregistration delay on the ALB target group to 300 seconds.
Why it's wrong here
Increasing the ALB deregistration delay to 300 seconds only extends the time that in-flight requests can finish after a task begins stopping; it does not change the underlying ECS deployment behavior. The old tasks will still be removed before new tasks are ready unless the deployment strategy itself maintains capacity, so the application will experience downtime during task replacement. This setting is a complementary measure, not a complete solution.
- ✗
Use a blue/green deployment with CodeDeploy and set the 'Minimum healthy percent' to 50.
Why it's wrong here
Blue/green deployment with CodeDeploy can achieve zero downtime, but setting 'Minimum healthy percent' to 50 is not the appropriate mechanism—this parameter belongs to ECS rolling updates, not to CodeDeploy blue/green traffic shifting. Interpreting it as a capacity threshold would allow the service to operate with only half the desired number of tasks, risking insufficient capacity and potential outages under load. A correct blue/green configuration should shift traffic to a fully scaled new task set before terminating old tasks.
- ✓
Configure the ECS service to use a rolling update with a minimum healthy percent of 100 and a maximum percent of 200.
Why this is correct
This rolling update configuration ensures that ECS starts new tasks up to twice the desired count (maximum percent 200) before terminating any existing tasks, while the minimum healthy percent of 100 guarantees that the service never drops below the desired number of running tasks. Because new tasks are registered with the load balancer and pass health checks before old tasks are stopped, traffic is served continuously without interruption. This is the classic zero-downtime deployment strategy for ECS services behind an ALB.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SOA-C02 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 SOA-C02 exam.