Cloud Technology and Services: choosing the right service category
Cloud Technology and Services is 34% of the exam. You are not designing architectures; you are picking the right service category for a one-paragraph scenario.
Compute
EC2 gives full control of the OS. Purchasing options: On-Demand; Savings Plans and Reserved Instances for committed steady use; Spot for fault-tolerant batch work at up to 90% off, interruptible with a two-minute warning; Dedicated Hosts for licensing or compliance. Lambda runs code without servers, billed per request and duration. Containers run on ECS or EKS, with Fargate providing serverless container capacity. Elastic Beanstalk deploys applications without managing the underlying infrastructure.
Storage
S3 is object storage with classes: Standard, Intelligent-Tiering (moves objects automatically when access is unknown), Standard-IA, One Zone-IA, Glacier Instant Retrieval, Glacier Flexible Retrieval, and Glacier Deep Archive. EBS is block storage for one EC2 instance and is locked to a single Availability Zone. EFS is shared NFS file storage for Linux; FSx covers Windows/SMB and high-performance file workloads.
Databases and networking
RDS for managed relational engines; Aurora for AWS's high-performance MySQL/PostgreSQL-compatible engine; DynamoDB for serverless key-value at any scale; Redshift for analytics warehouses; ElastiCache for in-memory caching. A VPC spans a Region, and each subnet sits in exactly one Availability Zone. Security groups are stateful and allow-only; network ACLs are stateless and support allow and deny. Route 53 is DNS, CloudFront is the CDN, Direct Connect is a private dedicated link, and ELB distributes traffic.
Worked example
A regulator requires seven years of log retention, retrieval within 12 hours, at the lowest cost. S3 Standard and Standard-IA fail on price. Glacier Flexible Retrieval fits the window (standard retrieval 3–5 hours) but costs more than Deep Archive, which also meets the 12-hour standard retrieval. Because both satisfy the constraint, price decides: Deep Archive wins. Had the requirement been milliseconds, the answer would be Glacier Instant Retrieval or Standard.
Traps
Attaching an EBS volume to an instance in another AZ; treating S3 as a file system; writing deny rules in a security group; assuming one subnet spans AZs; choosing Redshift for transactional writes or DynamoDB for SQL joins.