Application integration services: choosing the right one

The services at a glance

The Application Integration category of the exam covers six services. They all help components talk to each other without being tightly coupled, so that one part of a system can fail, slow down, or scale without breaking the others. Each service name links to its own tutorial, which covers its security, resilience, performance, and cost in depth.

Service	What it does
Amazon SQS	Message queues: a producer leaves messages and consumers pull them when they are ready
Amazon SNS	Topics that push each message to every subscriber: queues, functions, HTTPSHTTPS (HTTP Secure)HTTP sent over a TLS-encrypted connection, so that requests and responses cannot be read or changed on the way, and the server proves its identity with a certificate.Glossary entryClose endpoints, email, SMS, and mobile apps
Amazon EventBridge	Event buses that route events from AWS services, your applications, and SaaS partners to targets by rules; also Pipes and Scheduler
AWS Step Functions	Workflows (state machines) that run steps in order, in parallel, or by choice, with retries and error handling
Amazon MQ	Managed Apache ActiveMQ and RabbitMQ brokers, for applications that already use those brokers and their protocols
Amazon AppFlow	Transfers data between SaaS applications, such as Salesforce or Zendesk, and AWS services such as Amazon S3 and Amazon Redshift, with no code

Four integration patterns

Most questions in this category come down to choosing a pattern. Name the pattern first, and the service usually follows.

1. Queue (one message, one consumer): the producer sends work to a queue and a consumer pulls it when it has capacity. The queue absorbs bursts and holds messages while consumers are down. This is SQS, or Amazon MQ for existing brokers.
2. Topic (one message, every subscriber): the producer publishes once, and the service pushes a copy to each subscriber. This is SNS. Publishing to a topic with several SQS queues subscribed is the fanoutFan-outSending one message or event to many receivers at once so that each can process it in parallel, such as an Amazon SNS topic delivering to several SQS queues.Glossary entryClose pattern.
3. Event bus (route events by their content): sources send events, and rules decide which targets receive each one, based on fields in the event. This is EventBridge, which also receives events from AWS services and SaaS partners without any code. The comparisons here describe the bus with rules, now called Custom Event Bus - Classic, which does not order or deduplicate events. The 2026 Custom Event Bus adds retention, ordered delivery, deduplication, and sharing through AWS RAM, but exam scenarios are written for rules and targets.
4. Workflow (coordinate steps): one service calls the steps of a process in order, waits, retries, and handles failures. This is Step Functions.

Moving data in bulk between SaaS applications and AWS is a fifth job, which is AppFlow.

Reverse mindmap: from the question to the service

Exam scenarios describe the requirement, not the service. Find the kind of problem the question describes, then follow its clue to the service.

• Work is handed off to be done later
  • Decouple tiers, absorb bursts, consumers pull→ leads to Amazon SQS
  • Strict order or no duplicates→ leads to SQS FIFO queue
  • Scale workers on queue depth→ leads to SQS with Auto Scaling on backlog per instance
  • Failed messages kept for later analysis→ leads to Dead-letter queue
• One message reaches many receivers
  • Same message to several queues or services→ leads to SNS fanout to SQS
  • Each subscriber gets only some messages→ leads to SNS filter policy
  • Email, SMS, or mobile push to people→ leads to Amazon SNS
• Something happened and others react
  • React to AWS service events or API calls→ leads to EventBridge rule
  • Events from a SaaS application such as Zendesk→ leads to EventBridge partner event bus
  • Run a task on a schedule or once at a set time→ leads to EventBridge Scheduler
  • One source to one target with filter and enrichment→ leads to EventBridge Pipes
• Steps must be coordinated
  • Order, branching, retries, human approval→ leads to Step Functions
  • Long-running and auditable, exactly once→ leads to Step Functions Standard workflow
  • High-volume and short-lived→ leads to Step Functions Express workflow
• An existing system or SaaS app is involved
  • Existing ActiveMQ or RabbitMQ, JMS or AMQP→ leads to Amazon MQ
  • Move Salesforce or SaaS data to S3 or Redshift, no code→ leads to Amazon AppFlow

Commonly confused pairs

If the choice is between	Choose the first when	Choose the second when
SQS or SNS	One consumer group pulls work at its own pace	Every subscriber must get its own copy right away
SNS or EventBridge (bus with rules)	You need fast, high-volume fanout, or push to email, SMS, or mobile	You route by event content, receive AWS or SaaS events, or need archive and replay
SQS or Kinesis Data Streams	Each message is processed once and then deleted	Several applications read the same ordered records, or need replay
SQS or Amazon MQ	You build new cloud applications	Existing applications use ActiveMQ, RabbitMQ, or protocols such as JMS, AMQP, MQTT, or STOMP
Step Functions or SQS	You need to coordinate a sequence of steps	You only need to buffer work between two components

Key takeaways

• Name the pattern first: queue, topic, event bus, or workflow.
• "Decouple", "buffer", and "absorb spikes" point to SQS; "ordering" and "exactly-once processingExactly-once processingEach message is delivered and processed once, with no duplicates. Amazon SQS FIFO queues remove duplicate messages sent within a 5-minute deduplication interval.Glossary entryClose" point to SQS FIFOFIFO (First in, first out)Processing items in the order they arrived. Amazon SQS FIFO queues keep messages in order within a message group and remove duplicates.Glossary entryClose.
• "Fanout" and "notify subscribers" point to SNS; "react to AWS events" and "SaaS events" point to EventBridge.
• "Coordinate steps with retries and branching" points to Step Functions.
• "Existing broker" or "industry-standard messaging protocols" points to Amazon MQ; "SaaS data into S3 or Redshift" points to AppFlow.

Sources

• AWS Certification: SAA-C03 in-scope AWS services
• Amazon SQS Developer Guide: Amazon SQS queue types
• Amazon SNS Developer Guide: What is Amazon SNS?
• Amazon EventBridge User Guide: What is Amazon EventBridge?
• Amazon EventBridge User Guide: What is the EventBridge Custom Event Bus?
• AWS Step Functions Developer Guide: What is Step Functions?
• Amazon MQ Developer Guide: What is Amazon MQ?
• Amazon AppFlow User Guide: What is Amazon AppFlow?