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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. Shell $ sam init Choose for AWS Quick Start Template. Shell Which template source would you like to use? 1 - AWS Quick Start Templates 2 - Custom Template Location Choice: 1 Choose for package type Zip. Shell 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: 1 Choose Java11. Shell 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: 5 Choose Maven as build tool. Shell Which dependency manager would you like to use? 1 - maven 2 - gradle Dependency manager: 1 Choose myawssamplanet as project name. Shell Project name [sam-app]: myawssamplanet Choose the Hello World Example: Maven. Shell 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: 1 The SAM project is created. Shell ----------------------- 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.md The generated application has the following contents: events directory: contains an event.json file 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: YAML 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.Arn In 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: Java public class LambdaJava implements RequestHandler, String> { private static final Gson GSON = new GsonBuilder().setPrettyPrinting().create(); @Override public String handleRequest(Map 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. Java public class LambdaJava implements RequestHandler { 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 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: Shell $ 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 --guided After building the application, you deploy SAM. Choose myawssamplanet as stack name for CloudFormation. Shell $ sam deploy --guided Configuring SAM deploy ====================== Looking for config file [samconfig.toml] : Not found Setting default arguments for 'sam deploy' ========================================= Stack Name [sam-app]: myawssamplanet Leave the default of the AWS Region and enter y in order to confirm changes before deploy. Shell 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]: y Choose Y to allow role creation. Shell #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]: Y Do not disable rollback. Shell #Preserves the state of previously provisioned resources when an operation fails Disable rollback [y/N]: N The API will be publicly available, so choose y. Shell MyAwsSamFunction may not have authorization defined, Is this okay? [y/N]: y Save the arguments to a configuration file. Shell Save arguments to configuration file [Y/n]: Y Leave the defaults for the configuration file name and for the configuration environment. Shell 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). Shell 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::changeSet/samcli-deploy1643551688/4b3d5e55-adc8-44d7-8011-e8b1e17d9b9f Previewing CloudFormation changeset before deployment ====================================================== Deploy this changeset? [y/N]: y All the resources are created by the CloudFormation stack. Shell 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-3 Navigate 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. Shell $ curl https://5w9uji7dag.execute-api.eu-west-3.amazonaws.com/Prod/myawslambdajava/ Version 1 5. 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. Shell $ 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. Shell $ curl http://127.0.0.1:3000/myawslambdajava Version 1 It 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. Shell $ sam local invoke "MyAwsSamPlanet" -e events/event.json 6. 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. YAML 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: post Again, build and deploy SAM. Wait until the deployment has been finished and POST a request. Shell $ 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 1 Navigate 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. Shell EVENT: { "brand": "FORD", "type": "Kuga" } EVENT TYPE: class com.amazonaws.services.lambda.runtime.events.APIGatewayProxyRequestEvent Car brand: FORD Car type: Kuga 7. 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. XML junit junit 4.13.1 test 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. Shell $ aws cloudformation delete-stack --stack-name myawssamplanet --region eu-west-3 You 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. Shell $ aws cloudformation delete-stack --stack-name aws-sam-cli-managed-default --region eu-west-3 9. 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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