Applications Flashcards
What is SQS?
A pull based web service that gives you access to a message queue that can be used to store messages while waiting for a computer to process them. Each message is limited to 256 kb in size.
True or False. Using Amazon SQS, you can decouple the components of an application so they run independently, easing message management between components.
True. The word decouple usually leads to SQS.
What is a standard queue?
Nearly-unlimited number of transactions per second. Occasionally more than one copy of a message might be delivered out of order.
What is a FIFO queue?
First in first out delivery and exactly-once processing. Duplicates are not introduced into the queue. Limited to 300 transaction per second
When should you use FIFO queue over standard queue?
- If the order of processing matters
- If you would not want something to be processed more than once (even accidentally)
What is visibility timeout with SQS?
The amount of time that the message is invisible in the SQS queue after a reader picks up that message. Provided the job is processed before the visibility timeout expires, the message will then be deleted from the queue. If the job is not processed within that time, the message will become visible again and another reader will process it. This could result in the same message being delivered twice.
What is SQS long polling?
A way to retrieve messages from your Amazon SQS queues. While the regular short polling returns immediately (even if the message queue being polled is empty), long-polling doesn’t return a response until a message arrives in the message queue, or the long poll times out. This is a way to save money. Will help your EC2 not have to constantly poll the SQS queue.
What is SWF?
Simple Work Flow Service. A web service that makes it easy to coordinate work across distributed application components. SWF enables applications for a range of use cases, including media processing, web application back-ends, business process workflows, and analytics pipelines, to be designed as coordination of tasks.
What is the difference between SQS and SWF? List 4
- SQS has a retention period of up to 14 days; with SWF, workflow executions can last up to a year
- SWF presents a task-oriented API, whereas SQS offers a message-oriented API
- SWF ensures that the task is assigned only once and never duplicated. SQS needs to handle duplicated messages and may also need to ensure that a message is processed only once
- SWF keeps track of all the tasks and events in an application. SQS you need to implement your own application-level tracking especially if your application uses multiple queues
What are the different SWF actors?
- Workflow starters - initiate the workflow
- Deciders - control the flow of activity tasks
- activity workers - carry out activity tasks
What is SNS?
Simple Notification Service. Service that makes it easy to set up, operate, and send notifications from the cloud. Can work wtih several endpoints:
- SMS text message
- Email to SQS queues
- HTTP endpoints
True or False. SNS allows you to group multiple recipients using topics.
True. The topic is an access point for allowing recipients to dynamically subscribe for identical copies of the same notification.
What is Elastic Transcoder?
Media transcoder in the cloud. Convert media files from their original source format into different formats that will play on smartphones, tablets, PCs, etc. Provides transcoding presets for popular output formats, which means that you don’t need to guess about which settings work best on particular devices. Pay based on the minutes and resolution that you transcode.
What is API gateway?
A fully managed service that makes it easy for developers to publish, maintain, monitor, and secure APIs at any scale. A doorway into your aws environment. Typically used to communicate to Lambda functions.
True or False. API gateway can expose HTTPS endpoints to define a RESTful API.
True.
True or False. API gateway is limited to sending different targets to only one API endpoint.
False. It can send each API endpoint to a different target.
True or False. With API caching, you can reduce the number of calls made to your endpoint and also improve the latency of requests to your API.
True. When enabled, API Gatewaycaches response from your endpoint fro a specified time-to-live (TTL) period, in seconds. API gateway then responds to the request by looking up the endpoint response from the cache instead of making a request to your endpoint.
What is CORS and what is a workaround for?
- Cross-origin resource sharing is a mechanism that allows restricted resources on a web page to be requested from another domain outside the domain from which the first resource was served.
- It is a workaround for the same-origin policy. This policy is enforced by browsers to prevent cross-site scripting attacks.
What do you need to do if you see error “Origin policy cannot be read at the remote resource?”?
You need to enable CORS (cross-origin resource sharing) on API gateway.
What is Kinesis?
Platform on AWS to send all your streaming data. It makes it easy to load and analyze streaming data.