AWS Certification – Application Services – Cheat Sheet

SQS

• extremely scalable queue service and potentially handles millions of messages
• helps build fault tolerant, distributed loosely coupled applications
• stores copies of the messages on multiple servers for redundancy and high availability
• supports two queue types:
  • Standard Queues – guarantee At-Least-Once Delivery with best-effort ordering
  • FIFO Queues – guarantee Exactly-Once Processing and strict message ordering
• supports multiple readers and writers interacting with the same queue at the same time
• holds message for 4 days, by default, and can be changed from 1 min – 14 days after which the message is deleted
• maximum message size is 1 MiB for both Standard and FIFO queues (increased from 256 KB in Aug 2025)
• message needs to be explicitly deleted by the consumer once processed
• allows send, receive and delete batching which helps club up to 10 messages in a single batch (up to 256 KB total payload per batch) while charging price for a single message
• handles visibility of the message to multiple consumers using Visibility Timeout, where the message once read by a consumer is not visible to the other consumers till the timeout occurs
• can handle load and performance requirements by scaling the worker instances as the demand changes (Job Observer pattern)
• message sampling allowing short and long polling
  • returns immediately vs waits for fixed time for e.g. 20 secs
  • might not return all messages as it samples a subset of servers vs returns all available messages
  • repetitive vs helps save cost with long connection
• supports delay queues to make messages available after a certain delay, can be used to differentiate from priority queues
• supports dead letter queues (DLQ), to redirect messages which failed to process after certain attempts instead of being processed repeatedly
• supports DLQ redrive via the StartMessageMoveTask API to move messages from DLQ back to the source queue or a custom destination (supported for both Standard and FIFO queues)
• FIFO Queue High Throughput Mode
  • supports up to 70,000 transactions per second (TPS) per API action without batching
  • up to 700,000 messages per second with batching
  • available in selected regions (US East, US West, Europe Ireland)
• Fair Queues (2025) – mitigates noisy neighbor impact in multi-tenant systems by automatically detecting and deprioritizing tenants that generate excessive traffic, improving quality of service for other tenants
• supports dual-stack (IPv4 and IPv6) endpoints
• Lambda integration – supports provisioned mode for SQS event source mapping providing 3x faster scaling and 16x higher concurrency for event processing
• supports server-side encryption (SSE) using AWS KMS keys
• Design Patterns
  • Job Observer Pattern can help coordinate number of EC2 instances with number of job requests (Queue Size) automatically thus improving cost effectiveness and performance
  • Priority Queue Pattern can be used to setup different queues with different handling either by delayed queues or low scaling capacity for handling messages in lower priority queues

SNS

• delivery or sending of messages to subscribing endpoints or clients
• publisher-subscriber (pub/sub) model
• Producers and Consumers communicate asynchronously with subscribers by producing and sending a message to a topic
• supports two topic types:
  • Standard Topics – best-effort ordering, at-least-once delivery, nearly unlimited throughput
  • FIFO Topics – strict message ordering, exactly-once delivery, message deduplication
• supported subscription protocols: Email (plain or JSON), HTTP/HTTPS, SMS, SQS, Lambda, Kinesis Data Firehose
• supports Mobile Push Notifications to push notifications directly to mobile devices with services like Amazon Device Messaging (ADM), Apple Push Notification Service (APNS), Firebase Cloud Messaging (FCM) etc.
• Message Filtering – subscription filter policies allow subscribers to receive only a subset of messages published to the topic
  • supports filtering on message attributes or message body (filter policy scope)
  • up to 200 filter policies per topic, 10,000 per account
• Message Archiving and Replay (FIFO topics) – stores messages within the topic archive for up to 365 days and allows subscribers to replay them on demand for recovery or state synchronization
• High-Throughput Mode for FIFO Topics (Jan 2025) – increases throughput from default 300 MPS per message group to much higher levels by setting FifoThroughputScope to MessageGroup
• Cross-Region delivery – supports delivery from an SNS topic in one opt-in Region to an SQS queue in another opt-in Region
• integrated with Lambda to invoke functions on notifications
• for Email notifications, use SNS or SES directly, SQS does not work

SWF

• orchestration service to coordinate work across distributed components
• helps define tasks, stores, assigns tasks to workers, define logic, tracks and monitors the task and maintains workflow state in a durable fashion
• helps define tasks which can be executed on AWS cloud or on-premises
• helps coordinating tasks across the application which involves managing intertask dependencies, scheduling, and concurrency in accordance with the logical flow of the application
• supports built-in retries, timeouts and logging
• supports manual tasks (human-in-the-loop)
• Characteristics
  • deliver exactly once
  • uses long polling, which reduces number of polls without results
  • Visibility of task state via API
  • Timers, signals, markers, child workflows
  • supports versioning
  • keeps workflow history for a user-specified time
• AWS SWF vs AWS SQS
  • task-oriented vs message-oriented
  • track of all tasks and events vs needs custom handling

Step Functions

• recommended replacement for SWF for most workflow orchestration use cases
• serverless visual workflow service to build distributed applications, automate processes, orchestrate microservices, and create data/ML pipelines
• uses Amazon States Language (ASL) JSON-based language to define state machines
• supports two workflow types:
  • Standard Workflows – long-running (up to 1 year), exactly-once execution, full execution history
  • Express Workflows – high-volume, short-duration (up to 5 min), at-least-once execution
• native integrations with 220+ AWS services without custom glue code
• supports HTTPS endpoints for calling third-party APIs directly
• Distributed Map state for large-scale parallel processing (e.g., processing millions of S3 objects)
• built-in error handling with Retry and Catch mechanisms
• provides visual workflow editor and execution visualization for debugging
• Step Functions vs SWF
  • JSON-based state machine vs programmatic deciders/workers
  • serverless, managed vs requires custom worker hosts
  • 220+ AWS integrations vs custom integration code
  • visual debugging vs API-based visibility

SES

• highly scalable and cost-effective email service
• SESv2 API is the recommended API – all new features are only available through SESv2 (SESv1 still supported but not receiving new capabilities)
• uses content filtering technologies to scan outgoing emails to check standards and email content for spam and malware
• supports full-fledged emails to be sent as compared to SNS where only the message is sent in Email
• ideal for sending bulk emails at scale
• guarantees first hop
• eliminates the need to support custom software or applications to do heavy lifting of email transport
• Virtual Deliverability Manager (VDM) – automatically adjusts email sending in real time to improve inbox placement
  • provides deliverability insights, optimization recommendations, and detailed dashboards
  • tracks open/click rates, bounce/complaint rates at ISP and configuration level
  • Advisor feature provides configuration recommendations for improved deliverability
• Mail Manager (2024) – advanced email routing and archiving capabilities
  • supports rule-based email processing with actions (invoke Lambda, bounce, archive)
  • Ingress Endpoint with optional TLS and mutual TLS (mTLS) certificate-based authentication
  • simplifies email infrastructure migrations
• supports both sending and receiving emails – incoming email can integrate with S3, Lambda, and SNS
• available in multiple AWS regions globally

EventBridge

• serverless event bus for building event-driven architectures (evolved from CloudWatch Events)
• supports custom events, AWS service events, and SaaS partner integrations (Stripe, Datadog, Zendesk, etc.)
• Event Bus – receives events and routes them to target services based on rules
• Rules – match incoming events using event patterns and route to one or more targets
• Schema Registry – automatically discovers and stores event schemas
• EventBridge Pipes – point-to-point integrations between event producers and consumers with optional filter, transform, and enrich steps (without writing custom code)
• EventBridge Scheduler – fully managed cron and rate-based scheduling for one-time or recurring tasks
• supports targets including Lambda, Step Functions, SQS, SNS, Kinesis, ECS, and more
• EventBridge vs SNS
  • content-based filtering on event structure vs attribute-based filtering
  • supports SaaS partner event sources vs no SaaS partner integration
  • schema discovery and registry vs no schema management
  • single target per rule (fan-out via multiple rules) vs fan-out to multiple subscribers per topic