Messaging and business applications: CLF-C02 study notes and practice questions
What to know about Messaging and business applications for the CLF-C02 exam, from the Cloud Technology and Services domain (34% of the exam guide), then 2 free questions to test it. Part of the CLF-C02 study guide.
Application integration services let separate parts of an application communicate without depending on each other directly. That’s called loose coupling, and it means one part can fail or slow down without breaking the rest.
Integration services
Service
What it does
Clue in the question
Amazon SQS
A message queue: one component sends messages, another processes them when ready
“Decouple”, “buffer requests”, “process orders in the background”
Amazon SNS
Publish/subscribe: one message is pushed to many subscribers (email, SMS, SQS queues, Lambda)
“Notify several systems at once”, “send alerts”
Amazon EventBridge
An event bus that routes events from AWS services, your apps and SaaS apps to targets, plus schedules
“React when something happens”
AWS Step Functions
Coordinates multiple steps into a visual workflow with retries
“Orchestrate a multi-step process”
Amazon MQ
Managed message brokers (ActiveMQ, RabbitMQ)
“Move an existing app that uses a standard message broker”
Amazon API Gateway
Create and manage APIs in front of back-end services
“Expose a REST API”
AWS AppSync
Managed GraphQL APIs
“GraphQL”
Business application services
Need
Service
Send marketing or transactional email
Amazon SES
Cloud contact center
Amazon Connect
Common traps
SQS vs SNS. SQS holds messages until one consumer processes each; SNS pushes each message to every subscriber immediately. A common pattern uses SNS to fan out to several SQS queues.
SNS vs SES. SNS sends notifications (including simple emails); SES is a full email sending service for applications.
EventBridge vs SNS. EventBridge routes events by their content and connects to many AWS and SaaS sources.
When a customer places an order, a shop wants one message to be delivered at the same time to an Amazon SQS queue for fulfillment, another SQS queue for analytics, and an email address for the sales manager.
Which service should publish the message?
Choose one answer.
AA. Amazon SQS on its own, using one queue shared by all three consumers
BB. Amazon Simple Email Service (Amazon SES) on its own
CC. Amazon Simple Notification Service (Amazon SNS)
DD. AWS Step Functions, which runs a sequence of workflow steps
Show the answer and explanation
Answer: C
A. Wrong: A queue holds messages for consumers to pick up. One queue cannot copy a message into two other queues or send it as an email.
B. Wrong: SES sends email, but it cannot deliver the same message to SQS queues. The fulfillment and analytics queues would receive nothing.
D. Wrong: Step Functions coordinates ordered steps in a workflow. It is not designed to deliver one message to queues and email at the same time.
Explanation
Amazon SNS fans out one published message to several subscribers, including SQS queues and email endpoints, at the same time. The other options each reach only one kind of destination, or coordinate steps rather than delivering copies.
B. Wrong: SQS holds messages for other services to process. It does not send email to customers.
C. Wrong: EventBridge routes events from sources to targets. It does not send email to customers by itself.
D. Wrong: IoT Core connects devices to AWS over protocols such as MQTT. It is built for devices, not for sending email.
Explanation
Amazon SES is AWS's email sending service, and verifying the bakery's domain lets its emails come from that domain. The other services handle queued messages, event routing or devices, so none of them sends email to customers.
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