An Introduction to AWS Serverless Application Model
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Join For FreeIn this blog, the AWS Serverless Application Model (AWS SAM) is introduced. You will learn what SAM is and where it can be used for. You will also get your hands dirty, because you will create an AWS SAM project from scratch. Enjoy!
1. Introduction
AWS SAM is, according to the official documentation, a framework that you can use to build serverless applications on AWS . A serverless application consists of several lambda’s and other resources working together. In order to define all of these components, a SAM template is used. This SAM template is used to deploy the application to AWS. During deployment, the SAM template is converted to a CloudFormation template which will actually create the resources defined in the SAM template. An introduction to AWS CloudFormation is given in a previous post. SAM can be seen as a CloudFormation++ where less configuration is needed in the template itself. E.g. the Events property in a SAM template will create an API gateway for the Lambda but with less yaml than you would need in a CloudFormation template. You will see for yourself later on in this post. Another big advantage of SAM is that you can easily test it locally on your dev machine.
Enough talking, let’s get started! In a previous post, a Java Lambda with an API gateway was created. You will use the code of that Lambda for deploying the application using SAM. The code for the Lambda is available at GitHub. The resulting SAM template and Lambda used in this blog, is also available at GitHub.
The step-by-step guide is inspired by the AWS Getting Started tutorial. However, in this post you will use a Java Lambda instead of Python and you will see what you need to change to the Lambda created in a previous post in order to let it work with SAM.
A prerequisite is that you have the SAM CLI installed, instructions can be found here.
2. Creating the SAM Application
The easiest way to get started, is to start from an example application.
$ sam initChoose for AWS Quick Start Template.
Which template source would you like to use?
1 - AWS Quick Start Templates
2 - Custom Template Location
Choice: 1Choose for package type Zip.
What package type would you like to use?
1 - Zip (artifact is a zip uploaded to S3)
2 - Image (artifact is an image uploaded to an ECR image repository)
Package type: 1Choose Java11.
Which runtime would you like to use?
1 - nodejs14.x
2 - python3.8
3 - ruby2.7
4 - go1.x
5 - java11
6 - dotnetcore3.1
7 - nodejs12.x
8 - nodejs10.x
9 - python3.7
10 - python3.6
11 - python2.7
12 - ruby2.5
13 - java8.al2
14 - java8
15 - dotnetcore2.1
Runtime: 5Choose Maven as build tool.
Which dependency manager would you like to use?
1 - maven
2 - gradle
Dependency manager: 1Choose myawssamplanet as project name.
Project name [sam-app]: myawssamplanetChoose the Hello World Example: Maven.
Cloning app templates from https://github.com/aws/aws-sam-cli-app-templates
AWS quick start application templates:
1 - Hello World Example: Maven
2 - EventBridge Hello World: Maven
3 - EventBridge App from scratch (100+ Event Schemas): Maven
4 - Step Functions Sample App (Stock Trader): Maven
Template selection: 1The SAM project is created.
-----------------------
Generating application:
-----------------------
Name: myawssamplanet
Runtime: java11
Dependency Manager: maven
Application Template: hello-world
Output Directory: .
Next steps can be found in the README file at ./myawssamplanet/README.mdThe generated application has the following contents:
- events directory: contains an
event.jsonfile which can be used to test the lambda locally; - HelloWorldFunction: the sample application, you will replace this one;
- README.md: a readme file containing instructions what you can do with the sample application;
- template.yaml: this is the SAM template which contains the configuration of the resources that need to be created (similar as a CloudFormation template).
3. Customize SAM Project
In this section, you will customize the generated application in order to use the Java Lambda created in a previous post. Create a directory MyAwsSamFunction next to the HelloWorldFunction and copy the contents of the Java Lambda in this directory. Remove the HelloWorldFunction directory.
Change the template.yaml file in order that the references to the HelloWorldFunction are replaced with references to the MyAwsSamFunction. The resulting file is the following:
AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
myawssamplanet
Sample SAM Template for myawssamplanet
Globals:
Function:
Timeout: 20
Resources:
MyAwsSamFunction:
Type: AWS::Serverless::Function
Properties:
CodeUri: MyAwsSamFunction
Handler: com.mydeveloperplanet.myawslambdajavaplanet.LambdaJava::handleRequest
Runtime: java11
MemorySize: 512
Environment:
Variables:
PARAM1: VALUE
Events:
MyAwsLambdaJavaGet:
Type: Api
Properties:
Path: /myawslambdajava
Method: get
Outputs:
MyAwsSamApi:
Description: "API Gateway endpoint URL for Prod stage for LambdaJava function"
Value: !Sub "https://${ServerlessRestApi}.execute-api.${AWS::Region}.amazonaws.com/Prod/myawslambdajava/"
MyAwsSamFunction:
Description: "LambdaJava Lambda Function ARN"
Value: !GetAtt MyAwsSamFunction.Arn
MyAwsSamFunctionIamRole:
Description: "Implicit IAM Role created for LambdaJava function"
Value: !GetAtt MyAwsSamFunctionRole.ArnIn the Resources section, the Lambda is defined and a MyAwsLambdaJavaGet Event of type Api. The latter will create an API Gateway containing a Rest resource where the Lambda can be invoked by means of a GET request.
A complete overview of the different sections is described here.
You also need to change the LambdaJava class. The current implementation makes us of the Lambda Integration type in the API Gateway. However, by default, SAM will make use of the Lambda Proxy Integration type. The difference is that the payload is sent differently from API Gateway to the Lambda function. If you do not change this, an Internal Server error will be sent as a response when you invoke the Rest resource. The current implementation is the following:
public class LambdaJava implements RequestHandler<Map<String, String>, String> {
private static final Gson GSON = new GsonBuilder().setPrettyPrinting().create();
@Override
public String handleRequest(Map<String, String> event, Context context) {
LambdaLogger logger = context.getLogger();
String response = "Version 1";
...
return response;
}
}Instead, you need to implement the handleRequest which takes an APIGatewayProxyRequestEvent object. You also need to replace GSON.toJson(input) with input.getBody() and the response needs be formatted a little bit different. Besides that, also a null-check needs to be added in case the body is empty, otherwise a NullPointerException will be thrown.
public class LambdaJava implements RequestHandler<APIGatewayProxyRequestEvent, APIGatewayProxyResponseEvent> {
private static final Gson GSON = new GsonBuilder().setPrettyPrinting().create();
@Override
public APIGatewayProxyResponseEvent handleRequest(final APIGatewayProxyRequestEvent input, final Context context) {
LambdaLogger logger = context.getLogger();
// log execution details
logger.log("ENVIRONMENT VARIABLES: " + GSON.toJson(System.getenv()) + System.lineSeparator());
logger.log("CONTEXT: " + GSON.toJson(context) + System.lineSeparator());
// process event
logger.log("EVENT: " + input.getBody() + System.lineSeparator());
logger.log("EVENT TYPE: " + input.getClass() + System.lineSeparator());
if (input.getBody() != null) {
// Parse JSON into an object
Car car = GSON.fromJson(input.getBody(), Car.class);
logger.log("Car brand: " + car.getBrand() + System.lineSeparator());
logger.log("Car type: " + car.getType() + System.lineSeparator());
}
Map<String, String> headers = new HashMap<>();
headers.put("Content-Type", "application/text");
headers.put("X-Custom-Header", "application/text");
APIGatewayProxyResponseEvent response = new APIGatewayProxyResponseEvent()
.withHeaders(headers);
return response
.withStatusCode(200)
.withBody("Version 1");
}
}4. Build and Deploy
Now it is time to build and deploy SAM. Navigate to the directory where the template.yaml exists and execute the build command:
$ sam build
Building codeuri: /home/../myawssamplanet/MyAwsSamFunction runtime: java11 metadata: {} architecture: x86_64 functions: ['MyAwsSamFunction']
Running JavaMavenWorkflow:CopySource
Running JavaMavenWorkflow:MavenBuild
Running JavaMavenWorkflow:MavenCopyDependency
Running JavaMavenWorkflow:MavenCopyArtifacts
Build Succeeded
Built Artifacts : .aws-sam/build
Built Template : .aws-sam/build/template.yaml
Commands you can use next
=========================
[*] Invoke Function: sam local invoke
[*] Test Function in the Cloud: sam sync --stack-name {stack-name} --watch
[*] Deploy: sam deploy --guidedAfter building the application, you deploy SAM. Choose myawssamplanet as stack name for CloudFormation.
$ sam deploy --guided
Configuring SAM deploy
======================
Looking for config file [samconfig.toml] : Not found
Setting default arguments for 'sam deploy'
=========================================
Stack Name [sam-app]: myawssamplanetLeave the default of the AWS Region and enter y in order to confirm changes before deploy.
AWS Region [eu-west-3]:
#Shows you resources changes to be deployed and require a 'Y' to initiate deploy
Confirm changes before deploy [y/N]: yChoose Y to allow role creation.
#SAM needs permission to be able to create roles to connect to the resources in your template
Allow SAM CLI IAM role creation [Y/n]: YDo not disable rollback.
#Preserves the state of previously provisioned resources when an operation fails
Disable rollback [y/N]: NThe API will be publicly available, so choose y.
MyAwsSamFunction may not have authorization defined, Is this okay? [y/N]: ySave the arguments to a configuration file.
Save arguments to configuration file [Y/n]: YLeave the defaults for the configuration file name and for the configuration environment.
SAM configuration file [samconfig.toml]:
SAM configuration environment [default]:The CloudFormation stacks are created. Take a look at AWS CloudFormation in the AWS Management console.
Choose y to deploy the application (at the bottom of the output below).
Looking for resources needed for deployment:
Creating the required resources...
Successfully created!
Managed S3 bucket: aws-sam-cli-managed-default-samclisourcebucket-o08u00g288r9
A different default S3 bucket can be set in samconfig.toml
Saved arguments to config file
Running 'sam deploy' for future deployments will use the parameters saved above.
The above parameters can be changed by modifying samconfig.toml
Learn more about samconfig.toml syntax at
https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-cli-config.html
Uploading to myawssamplanet/8e80317f02e0baccb04761d59791c6ad 2667728 / 2667728 (100.00%)
Deploying with following values
===============================
Stack name : myawssamplanet
Region : eu-west-3
Confirm changeset : True
Disable rollback : False
Deployment s3 bucket : aws-sam-cli-managed-default-samclisourcebucket-o08u00g288r9
Capabilities : ["CAPABILITY_IAM"]
Parameter overrides : {}
Signing Profiles : {}
Initiating deployment
=====================
Uploading to myawssamplanet/a0f8a035e37699e9be00c92f8d0d10fe.template 1308 / 1308 (100.00%)
Waiting for changeset to be created..
CloudFormation stack changeset
-------------------------------------------------------------------------------------------------------------------------------------------------------------
Operation LogicalResourceId ResourceType Replacement
-------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Add MyAwsSamFunctionMyAwsLambdaJavaGetPer AWS::Lambda::Permission N/A
missionProd
+ Add MyAwsSamFunctionRole AWS::IAM::Role N/A
+ Add MyAwsSamFunction AWS::Lambda::Function N/A
+ Add ServerlessRestApiDeployment4aeac94236 AWS::ApiGateway::Deployment N/A
+ Add ServerlessRestApiProdStage AWS::ApiGateway::Stage N/A
+ Add ServerlessRestApi AWS::ApiGateway::RestApi N/A
-------------------------------------------------------------------------------------------------------------------------------------------------------------
Changeset created successfully. arn:aws:cloudformation:eu-west-3:<account ID>:changeSet/samcli-deploy1643551688/4b3d5e55-adc8-44d7-8011-e8b1e17d9b9f
Previewing CloudFormation changeset before deployment
======================================================
Deploy this changeset? [y/N]: yAll the resources are created by the CloudFormation stack.
2022-01-30 15:11:17 - Waiting for stack create/update to complete
CloudFormation events from stack operations
-------------------------------------------------------------------------------------------------------------------------------------------------------------
ResourceStatus ResourceType LogicalResourceId ResourceStatusReason
-------------------------------------------------------------------------------------------------------------------------------------------------------------
CREATE_IN_PROGRESS AWS::IAM::Role MyAwsSamFunctionRole -
CREATE_IN_PROGRESS AWS::IAM::Role MyAwsSamFunctionRole Resource creation Initiated
CREATE_COMPLETE AWS::IAM::Role MyAwsSamFunctionRole -
CREATE_IN_PROGRESS AWS::Lambda::Function MyAwsSamFunction -
CREATE_IN_PROGRESS AWS::Lambda::Function MyAwsSamFunction Resource creation Initiated
CREATE_COMPLETE AWS::Lambda::Function MyAwsSamFunction -
CREATE_IN_PROGRESS AWS::ApiGateway::RestApi ServerlessRestApi -
CREATE_COMPLETE AWS::ApiGateway::RestApi ServerlessRestApi -
CREATE_IN_PROGRESS AWS::ApiGateway::RestApi ServerlessRestApi Resource creation Initiated
CREATE_IN_PROGRESS AWS::Lambda::Permission MyAwsSamFunctionMyAwsLambdaJavaGetPer -
missionProd
CREATE_IN_PROGRESS AWS::ApiGateway::Deployment ServerlessRestApiDeployment4aeac94236 -
CREATE_IN_PROGRESS AWS::Lambda::Permission MyAwsSamFunctionMyAwsLambdaJavaGetPer Resource creation Initiated
missionProd
CREATE_IN_PROGRESS AWS::ApiGateway::Deployment ServerlessRestApiDeployment4aeac94236 Resource creation Initiated
CREATE_COMPLETE AWS::ApiGateway::Deployment ServerlessRestApiDeployment4aeac94236 -
CREATE_IN_PROGRESS AWS::ApiGateway::Stage ServerlessRestApiProdStage -
CREATE_IN_PROGRESS AWS::ApiGateway::Stage ServerlessRestApiProdStage Resource creation Initiated
CREATE_COMPLETE AWS::ApiGateway::Stage ServerlessRestApiProdStage -
CREATE_COMPLETE AWS::Lambda::Permission MyAwsSamFunctionMyAwsLambdaJavaGetPer -
missionProd
CREATE_COMPLETE AWS::CloudFormation::Stack myawssamplanet -
-------------------------------------------------------------------------------------------------------------------------------------------------------------
CloudFormation outputs from deployed stack
-------------------------------------------------------------------------------------------------------------------------------------------------------------
Outputs
-------------------------------------------------------------------------------------------------------------------------------------------------------------
Key MyAwsSamFunction
Description LambdaJava Lambda Function ARN
Value arn:aws:lambda:eu-west-3::function:myawssamplanet-MyAwsSamFunction-H9zkMo3NEWsn
Key MyAwsSamApi
Description API Gateway endpoint URL for Prod stage for LambdaJava function
Value https://5w9uji7dag.execute-api.eu-west-3.amazonaws.com/Prod/myawslambdajava/
Key MyAwsSamFunctionIamRole
Description Implicit IAM Role created for LambdaJava function
Value arn:aws:iam:::role/myawssamplanet-MyAwsSamFunctionRole-XNX3QIEXXG93
-------------------------------------------------------------------------------------------------------------------------------------------------------------
Successfully created/updated stack - myawssamplanet in eu-west-3Navigate to the API Gateway service and you notice that the API Gateway is created.
Navigate to the Lambda service and you notice that the Lambda is created.
The public URL for the API Gateway is shown in the console output. Try to access the URL. As expected, ‘Version 1’ is returned.
$ curl https://5w9uji7dag.execute-api.eu-west-3.amazonaws.com/Prod/myawslambdajava/
Version 15. Test Locally
One of the main advantages of using SAM, is that you can test it locally. You can test the application including an API Gateway by using the local start-api command.
$ sam local start-api
Mounting MyAwsSamFunction at http://127.0.0.1:3000/myawslambdajava [GET]
You can now browse to the above endpoints to invoke your functions. You do not need to restart/reload SAM CLI while working on your functions, changes will be reflected instantly/automatically. You only need to restart SAM CLI if you update your AWS SAM template
2022-01-30 15:35:39 * Running on http://127.0.0.1:3000/ (Press CTRL+C to quit)Open a new Terminal and try to invoke the API Gateway resource.
$ curl http://127.0.0.1:3000/myawslambdajava
Version 1It might take some seconds before the response is returned. In the meanwhile, the terminal where you started the API, outputs the serverlogging. Here you notice that a Docker container is started.
It is also possible to invoke the Lambda directly by simulating the event which is normally sent from the API Gateway to the Lambda. This is where the event.json file comes in handy.
$ sam local invoke "MyAwsSamPlanet" -e events/event.json6. Add Post Request
The Lambda which is used, actually takes a JSON body, converts JSON objects into Java objects and prints it to the logging. Add a MyAwsLambdaPost request to the template.yaml in order to test this behaviour.
Events:
MyAwsLambdaJavaGet:
Type: Api # More info about API Event Source: https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#api
Properties:
Path: /myawslambdajava
Method: get
MyAwsLambdaJavaPost:
Type: Api
Properties:
Path: /myawslambdajava
Method: postAgain, build and deploy SAM. Wait until the deployment has been finished and POST a request.
$ curl -i -X 'POST' \
> 'https://5w9uji7dag.execute-api.eu-west-3.amazonaws.com/Prod/myawslambdajava/' \
> -H 'accept: application/json' \
> -H 'Content-Type: application/json' \
> -d '{
> "brand": "FORD",
> "type": "Kuga"
> }'
HTTP/2 200
content-type: application/text
content-length: 9
date: Sun, 30 Jan 2022 14:54:22 GMT
x-amzn-requestid: b9855126-b51e-4dc9-abea-97dee77b5168
x-amz-apigw-id: Mw74sG6AiGYFoRg=
x-custom-header: application/text
x-amzn-trace-id: Root=1-61f6a69d-02ca6ba1368061e864cb7d6f;Sampled=0
x-cache: Miss from cloudfront
via: 1.1 415e8d76bf2c69e5e03b89ba8461cd7e.cloudfront.net (CloudFront)
x-amz-cf-pop: AMS50-C1
x-amz-cf-id: q1c-8WZOIqEhllZhGBAFQP8auu54fX7E3B41S2DcZNhr-HxV5JZLSQ==
Version 1Navigate to the Lambda service and navigate to the Monitor tab. From here, you can open the CloudWatch logging for the Lambda. The logging shows you that the event is received in the Lambda and converted to a Java object.
EVENT:
{
"brand": "FORD",
"type": "Kuga"
}
EVENT TYPE: class com.amazonaws.services.lambda.runtime.events.APIGatewayProxyRequestEvent
Car brand: FORD
Car type: Kuga7. Unit Test
For completeness, also a unit test is added to the git repository. It is not further explained in this blog, but the test can be viewed at GitHub. It is important to add the junit dependency to the pom.
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.13.1</version>
<scope>test</scope>
</dependency>You also need to ensure that the context and the logger are not null. It is not a very beautiful unit test, but it just works :-) .
8. Cleanup
As always, it is a good practice to clean up all the resources you have created after you are done experimenting with AWS services. Because CloudFormation is used, it is quite easy to delete all the resources by means of a single command.
$ aws cloudformation delete-stack --stack-name myawssamplanet --region eu-west-3You can follow the progress in CloudFormation.
SAM also created a S3 bucket, this one is not automatically deleted. Navigate to the S3 service. Select the created bucket and click the Empty button. Follow the instructions and click the Delete button in order to remove the S3 bucket.
Now you can also delete the aws-sam-cli-managed-default stack which was created.
$ aws cloudformation delete-stack --stack-name aws-sam-cli-managed-default --region eu-west-39. Conclusion
In this blog, you got an introduction of the Serverless Application Model of AWS. You also got your hands dirty and created by means of a SAM template an API Gateway and Java Lambda. You learnt how to build, deploy and test the application remotely and locally.
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