SOA-C03 practice question: Troubleshooting deployments (1 of 2)

Deployment, Provisioning, and Automation A free question from our original SOA-C03 practice exam. Try it, then open the answer to see why each option is right or wrong.

A logistics broker's Auto Scaling group spans two private /26 subnets. During a peak-season scale-out, the group's activity history shows failed launches with the message that there are not enough free addresses in the subnet. Other workloads also use these subnets, and the account has plenty of remaining EC2 vCPU quota. What should a CloudOps engineer do to allow the group to scale?

Choose one answer.

A. Request an increase to the EC2 On-Demand vCPU quota so that the group can launch more instances in the Region.
B. Edit the two subnets and change their CIDR blocks from /26 to /22 so that they contain more IP addresses.
C. Add a secondary CIDR block to the VPC, create larger subnets from it, and add them to the group.
D. Change the launch template to a larger instance type so that fewer instances are needed to serve the same load.

Show the answer and explanation

Answer: C

A. Wrong: The error is about IP addresses in the subnets, not compute quota. The account already has quota available, so an increase would not change anything. Learn more: Amazon EC2 service quotas (opens in a new tab)
B. Wrong: A subnet's CIDR block cannot be changed after the subnet is created. Larger address space needs new subnets. Learn more: Subnets for your VPC (opens in a new tab)
C. Right: Correct. A /26 subnet has only 59 usable addresses because AWS reserves five. A secondary CIDR provides room for larger subnets, and adding them to the group gives it addresses to launch into. Learn more: VPC CIDR blocks (opens in a new tab)
D. Wrong: Larger instances might reduce the count, but other workloads are still consuming the subnets. The group would hit the same limit at the next scale-out. Learn more: Troubleshoot Amazon EC2 Auto Scaling (opens in a new tab)

Explanation

Launch failures that mention free addresses mean the subnets have run out of IP addresses. Subnet CIDR blocks cannot be resized, so the fix is new subnets, from spare VPC space or a secondary CIDR block, added to the group. Quotas and instance types do not create addresses.

SOA-C03 practice question: Troubleshooting deployments (1 of 2)

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