Simple Workflow Service Flashcards
When to use Amazon SWF
have multiple tasks that need to be coordinated and executed in a specific sequence based on some dependency or in parallel.
multiple application components and need to dispatch tasks to these application components.
a distributed application and you need to coordinate and process tasks in a distributed application environment.
you need to execute ordered application steps.
need to manage the application state during distributed execution.
need to asynchronously execute event-driven tasks.
SWF
helps in building applications that can handle work through distributed components.
use cases of SWF
Media processing; Video encoding;
Customer order processing workflow.(processing large product catalogs using amazon Mechanical Turk)
Web application backend.
Business process workflow.(Migrating components from the datacenter to the cloud)
Analytics pipelines.
How workflow history helps
stores all details about the workflow execution and thus eliminates the need for the application to maintain the state.
provides the current status of each of the activities scheduled along with the result.
provides an audit trail.
Actors
a program or entity that performs different types of activities in a workflow.
workflow starter;
Decider;
Activity worker;
Decider
a program that decides the coordination logic of a workflow. like order of execution, concurrency, and scheduling etc. A decision is a data type in SWF, which represents next actions.
Activity worker
are programs that interact with SWF to get tasks, process received tasks, and return the results. receives tasks from SWF, executes the tasks and returns the result back to SWF. Programmatically, RegisterActivityType action to register the activity tasks.
using polling mechanism. workers can consist of a sever on EC2 or on-promise(database).
Tasks
work assignments to activity workers and deciders. 3 types: Activity task(a task assigned to worker); Lambda task; Decision task.(tell the decider that the state of the workflow execution has changed). allows the decider to determine what tasks to do next.
SWF Domains
mechanism to scope SWF resources such as workflows, activity types, workflow execution, and so on.
used to help determine the scope of workflows.
multiple work flows can live inside of a domain;
workflows cannot interact with work flows in other domains.
can be created at the level of account and may not be nested.
Object identifiers
workflow type;
Features
distributed;
can scale up or down depending on the task;
works with on-premises applications or applications on the cloud;
a workflow can consist of human events
workflows can last up to 1 year.
Guarantees order of execution.
SQS vs SWF
Both are used to create distributed systems
Both allow each task/component to scale independently
SQS uses “best effort” mesaging order and could have duplicates
SWF guarantees execution order and uses deciders for next instructions
SWF can have a human task as part of the workflow
SQS messages live up to14 days;
SWF workflow or task executions can last up to 1 year.
SWF allows for synchronous and asynchronous distributed processing.
What are the different ways to access SWF?
AWS SDK for Java, Ruby, .NET, and PHP
AWS Flow Framework for Java (Included in the AWS SDK for Java)
Amazon SWF web service APIs
AWS Management Console
Limits
maximum 10,000 workflow and activity types(in total).
maximum 100 Amazon SWF domains;
at any given time, max 100,000 open executions in a domain.
up for 1 year;
each workflow execution history can grow up to 25,000 events.
schedule up t 100 activity tasks in one decision.
1000 open activity tasks per owrkflow execution.
history of a completed execution up to 90 days.
SWF is available across AZs?
yes 3
