The trio to hold apart is SNS, SQS and EventBridge: all three move messages, and they move them differently. SNS pushes: one published message reaches every subscriber, which covers fan-out and alerting. SQS holds: messages wait in a queue until a consumer polls for them, which decouples a fast producer from a slow consumer and absorbs a burst without dropping work. EventBridge routes: an event is matched against rules and delivered to whichever targets those rules name. Scheduled invocations come from EventBridge Scheduler.
Step Functions is the one people reach for too early. A single event going to a single target is SNS, SQS or EventBridge. Step Functions belongs where several steps have order, branching, retries and state between them.
Among the end-user services the discriminator is persistence. A desktop that stays yours between sessions is WorkSpaces. An application streamed from a shared fleet is AppStream 2.0, which AWS has renamed Amazon WorkSpaces Applications; the in-scope list still carries the old name, so expect either. An internal web application reached through a managed browser is WorkSpaces Secure Browser.
The developer tools are a short set: CodeBuild builds and tests, CodePipeline sequences the stages, X-Ray traces the request, and the CLI is the programmatic way in. CodeDeploy and CodeArtifact sit outside the scope, so recognise them and move on.
Flash card
The remaining in-scope categories: application integration, business applications, developer tools, end-user computing, frontend and mobile, and IoT. Each is tested by recognising the job, not the configuration.
- Messaging and events: SNS publishes one message to every subscriber of a topic: SQS, Lambda, HTTP/S endpoints, email, SMS. SQS is a queue a consumer polls, decoupling components and absorbing bursts; standard and FIFO. EventBridge matches events against rules and delivers them to named targets, sourced from AWS services, your own applications and SaaS partners. EventBridge Scheduler runs cron and rate schedules.
- Orchestration and APIs: Step Functions sequences steps into a workflow, with state between them, Retry and Catch for errors, and Choice for branching. API Gateway creates, publishes and secures REST, HTTP and WebSocket APIs; it is in scope under networking. Amazon MQ, the managed ActiveMQ and RabbitMQ broker, is not in scope.
- Business applications: Amazon Connect is the contact centre, now branded Amazon Connect Customer in a wider portfolio. Amazon SES sends marketing and transactional email, and can receive mail. These two are the whole category in scope.
- Developer tools: the in-scope four are the AWS CLI, CodeBuild (compiles and tests), CodePipeline (automates release stages) and X-Ray (traces a request across services to the slow or failing call). CodeDeploy and CodeArtifact are out of scope.
- End-user computing: WorkSpaces provides persistent virtual desktops, one per user, on Windows or Linux. AppStream 2.0, renamed Amazon WorkSpaces Applications, streams applications and non-persistent desktops from a managed fleet. WorkSpaces Secure Browser delivers internal web applications through a managed browser.
- Frontend and IoT: AWS Amplify hosts frontend and full-stack web applications from a Git branch, with continuous deployment to the AWS global CDN. AWS IoT Core connects and manages devices over MQTT, MQTT over WSS, HTTPS and LoRaWAN.
Pick it when
Pick from this set when a scenario names a business outcome (a contact centre, an email campaign, a desktop for contractors, a device fleet) rather than an infrastructure property.
It's the wrong answer when
Don’t reach for SNS when one consumer pulls work at its own pace; that is SQS. Don’t reach for SQS when several systems must each receive the same message; that is SNS or EventBridge. Step Functions is oversized for one event going to one target.