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
• guarantees At-Least-Once Delivery, but does not guarantee Exact One Time Delivery which might result in duplicate messages (Not true anymore with the introduction of FIFO queues)
• does not maintain or guarantee message order, and if needed sequencing information needs to be added to the message itself (Not true anymore with the introduction of FIFO queues)
• supports multiple readers and writers interacting with the same queue as 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
• 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 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 sample 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 you used to differentiate from priority queues
• supports dead letter queues, to redirect messages which failed to process after certain attempts instead of being processed repeatedly
• 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 model
• Producers and Consumers communicate asynchronously with subscribers by producing and sending a message to a topic
• supports Email (plain or JSON), HTTP/HTTPS, SMS, SQS
• supports Mobile Push Notifications to push notifications directly to mobile devices with services like Amazon Device Messaging (ADM), Apple Push Notification Service (APNS), Google Cloud Messaging (GCM) etc. supported
• order is not guaranteed and No recall available
• 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
• 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

SES

• highly scalable and cost-effective email service
• 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