---
title: '22 Step Functions & AppSync'
disqus: hackmd
---

:::info
AWS Certified Developer Associate DVA-C01
:::

22 Step Functions & AppSync
===

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## Table of Contents

[TOC]

AWS Step Functions
---
- build serverless visual workflow to orchestrate lambda funcs
- represent flow as json state machine
- features
- sequence
- 1 func then another
- parallel
- 2 funcs at once
- conditions
- timeouts
- error handling
- retry and catch
- can also integrate with ec2, ecs, on premise servers, api gateway
- max execution time of 1 year
- possibility to implement human approval feature
- have human review before proceed with workflow
- use cases
- order fulfillment
- data processing
- web apps
- any workflow

### Visual Workflow
- get graph like this after designing state machine in json

### Error Handling
- any state can encounter runtime errors for various reasons
- state machine definition issues
- eg. no matching rule in choice state
- task failures
- eg. exception in lambda func
- transient issues
- eg. network partition events
- by default, when a state reports an error, aws step funcs causes the execution to fail entirely
- retrying failures - `Retry`
- `IntervalSeconds`, `MaxAttempts`, `BackoffRate`
- moving on - `Catch`
- `ErrorEquals`, `Next`
- best prac to include data in error msgs

### Standard vs Express
- express workflow is much cheaper
- intended for large num of workflow with small duration
- standard workflows for longer workflows with slower execution rate

### Console
- sequence batch func job

- hello world example in console

- can see entire execution event history and how long it took
- can also see input req/resp


- when u start new execution, can see visual workflow of it

- can see all execution from your parent state machine
- only applies to standard state machines

- when creating state machines, can choose from templates too

- eg. retry catch example

- eg. catch example
- falls to specific state based on error

AWS AppSync
---
- appsync is managed service that uses graphql
- graphql makes it easy for apps to get exactly the data they need
- new way of writing api
- includes combining data from 1 or more sources
- sources include nosql data stores, relational dbs, http apis
- integrates with dynamodb, aurora, elastisearch and others
- custom sources with aws lambda
- retrieve data in realtime with websocket or MQTT on websocket
- for mobile apps
- local data access
- data sync
- replacement for cookie to sync
- all starts with uploading 1 graphql schema

- graphql schema uploaded into appsync
- client does graphql query on appsync
- appsync runs it's own resolver
- resolver might be dynamodb so it does a fetch
- appsync sends graphql response in json back

- appsync can work with a multitude of apps
- at it's core, you have
- graphql schema
- resolver so it knows how to fetch data
- have direct integration with
- dynamodb
- aurora
- elastisearch
- lambda
- http
- cloudwatch metrics/logs to get info from appsync

### AppSync Security
- 4 ways u can authorise apps to interact with your aws appsync graphql api
- `API_KEY`
- `AWS_IAM`
- iam users/roles/cross acc access
- `OPENID_CONNECT`
- openid connect provider/json web token
- `AMAZON_COGNITO_USER_POOLS`
- for custom doamin and https, use cloudfront in front of appsync

### Console

- graphql schema example

- uses 2 dynamodb tables auto created


- queries is how we can start using our apis
- can test with the orange play btn
- mutations define the diff apis that can be used here

- reduce num of queries to backend



- default auth mode
- can use iam to have user enroll or cross acc access into appsync api


Quiz
---

###### tags: `AWS Developer Associate` `Notes`