---
title: '20 AWS Serverless Application Model (SAM)'
disqus: hackmd
---

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

20 AWS Serverless Application Model (SAM)
===

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## Table of Contents

[TOC]

AWS SAM
---
- serverless app model (sam)
- framework for developing and deploying serverless apps
- all config in yaml
- generate complex cloudformation from simple SAM YAML file
- supports anything from cloudformation
- outputs, mappings, params, res etc.
- only 2 commands to deploy to aws
- sam can use codedeploy to deploy lambda funcs
- sam can help you run lambda, api gateway, dynamodb locally
- dont need to deploy lambda func to test it

### What it Looks Like
- transform header indicating SAM template
- `Transform: 'AWS::Serverless-2016-10-31'`
- write code
- `AWS::Serverless::Function`
- lambda
- `AWS::Serverless::Api`
- api gateway
- `AWS:Serverless::SimpleTable`
- dynamodb
- package and deploy
- `aws cloudformation package / sam package`
- `aws cloudformation deploy / sam deploy`

### SAM Deployment
- aws cloudformation package
- upload code zip file to s3
- also transforms sam template into cloudformation template
- generated templates will have a reference to s3
- aws cloudformation deploy
- create and execute a change set
- change set is figuring out how cloudformation shld take its existing state and move it to the next state based on modifications generated
- cloudformation then applies it to our stack
- stack may comprise of all services

### SAM Policy Templates
- list of templates to apply perms to your lambda funcs
- full list [here](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-policy-templates.html)
- important examples
- `S3ReadPolicy`
- gives read only perms to objs in s3
- `SQSPollerPolicy`
- allows to poll on sqs queue
- `DynamoDBCrudPolicy`
- create read update delete

- instead of creating iam role, attach policy in sam template instead

### SAM with CodeDeploy
- sam framework natively uses codedeploy to update lambda functions
- leverage traffic shifting feature using aliases
- can also define pre and post traffic hooks features to validate deployment
- before traffic shift starts and after it ends
- easy & automated rollback using cloudwatch alarms

- trigger deployment in codedeploy
- runs pre traffic hook test using another lambda func
- optional
- do traffic shifting with alias
- then monitor cloudwatch alarm
- optional
- ensure everything goes well during deployment
- once deployment and traffic shifting done, run post-traffic hook lambda func
- also optional
- runs some tests on your alias
- if everything goes well, v1 func of alias goes away
- only left with v2

### Summary
- sam is built on cloudformation
- sam requires `Transform` and `Resources` section
- commands to know
- `sam build`
- fetch dependencies and create local deployment artifacts
- `sam package`
- package and upload to amazon s3
- generate CF template
- `sam deploy`
- deploy to cloudformation
- sam policy templates for easy iam policy definition
- sam is integrated with codedeploy to do deploy to lambda aliases

### Console
- https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-cli-install-windows.html
- follow this
- windows just download a sam installer
- use brew for mac and linux

#### Init Project
- use `sam init` to generate a sam template for your specific runtime
- but can also create from scratch on your own

- can go to sam examples github for dummy code
- https://github.com/aws/serverless-application-model


- example template yaml file
- `Transform` means sam template
- resource list
- 1st res is function
- handler shld be `<file name>.<function name>`
- codeuri shld point to dir with the code

- create cli commands to generate your transformed cloudformation template
- first create s3 bucket
- next upload code and do transformation from aws cloudformation package
- can also use `sam package` since sam is just shorthand for aws cloudformation

- generated template
- codeuri now points to s3
- running package will also output a sample deploy cli command

- failed as didnt add `CAPABILITY_IAM` into your cli cmd



- once deployed, can go to cloudformation to check your stack out

#### Adding API Gateway
- look for api gateway in the examples github for ref

- example lambda func for api gateway demo

- add events segment in lambda func to create new api
- func is invoked everytime a get req is called to /hello
- rerun your cloudformation commands to create the new api gateway


- more resources created for your cloudformation
- like api gateway and iam roles

#### Adding DynamoDB
- look for dynamodb example in github
- actually prev api gateway example alr used dynamodb so we'll just use that

- example lambda func for adding of dynamodb
- get region from os environment vars

- read doc for full list of properties u can pass into your simpletable segment
- set provisioned throughput to save costs for this demo

- add your simpletable section in the yaml file

- can add env vars in your yaml template
- table name refs the simpletable created
- region refs a pseudo param `AWS::Region`

- rmb to add iam policy to your func
- this basically gives a dynamodbcrudpolicy with ref to the table created to your lambda func

- sample function scans the dynamodb and returns it

#### CloudFormation Designer and App Repository
- can see details of what was created in cloudformation from viewing the stack
- pic above shows the template code

- can go actions > view designer

- high lvl view of what was created

- also when creating your lambda func, u have option to use aws serverless app repo
- is basically sam templates created by a lot of people
- can search through

#### SAM with CodeDeploy
- using sam hello world python example

- codeploy yaml to be integrated with your template yaml

- add `AutoPublishAlias` in your lambda func section in template yaml
- create new alias "live"
- also deployment pref specific canary 10% 10 mins
- 10% of traffic go to new ver for 10mins then shift 100%

- can also use `sam deploy --guided` instead of package and deploy
- run `sam build` before

- live alias created

- can view codedeploy traffic shift from codedeploy console

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