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Hello JSON

This is a simple example of an AWS Lambda function that takes a JSON structure as an input parameter and returns a JSON structure as a response.

The runtime takes care of decoding the input and encoding the output.

Code

The code defines HelloRequest and HelloResponse data structures to represent the input and output payloads. These structures are typically shared with a client project, such as an iOS application.

The code creates a LambdaRuntime struct. In it's simplest form, the initializer takes a function as an argument. The function is the handler that will be invoked when an event triggers the Lambda function.

The handler is (event: HelloRequest, context: LambdaContext). The function takes two arguments:

  • the event argument is a HelloRequest. It is the parameter passed when invoking the function.
  • the context argument is a Lambda Context. It is a description of the runtime context.

The function return value will be encoded to a HelloResponse as your Lambda function response.

Build & Package

To build & archive the package, type the following commands.

swift package archive --allow-network-connections docker

If there is no error, there is a ZIP file ready to deploy. The ZIP file is located at .build/plugins/AWSLambdaPackager/outputs/AWSLambdaPackager/HelloJSON/HelloJSON.zip

Deploy

Here is how to deploy using the aws command line.

# Replace with your AWS Account ID
AWS_ACCOUNT_ID=012345678901

aws lambda create-function \
--function-name HelloJSON \
--zip-file fileb://.build/plugins/AWSLambdaPackager/outputs/AWSLambdaPackager/HelloJSON/HelloJSON.zip \
--runtime provided.al2 \
--handler provided  \
--architectures arm64 \
--role arn:aws:iam::${AWS_ACCOUNT_ID}:role/lambda_basic_execution

The --architectures flag is only required when you build the binary on an Apple Silicon machine (Apple M1 or more recent). It defaults to x64.

Be sure to define the AWS_ACCOUNT_ID environment variable with your actual AWS account ID (for example: 012345678901).

Invoke your Lambda function

To invoke the Lambda function, use this aws command line.

aws lambda invoke \
--function-name HelloJSON \
--payload $(echo '{ "name" : "Seb", "age" : 50 }' | base64)  \
out.txt && cat out.txt && rm out.txt

Note that the payload is expected to be a valid JSON string.

This should output the following result.

{
    "StatusCode": 200,
    "ExecutedVersion": "$LATEST"
}
{"greetings":"Hello Seb. You look younger than your age."}

Undeploy

When done testing, you can delete the Lambda function with this command.

aws lambda delete-function --function-name HelloJSON