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Hello World

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

Code

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

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

  • the event argument is a String. 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 as your Lambda function response.

Test locally

You can test your function locally before deploying it to AWS Lambda.

To start the local function, type the following commands:

swift run

It will compile your code and start the local server. You know the local server is ready to accept connections when you see this message.

Building for debugging...
[1/1] Write swift-version--644A47CB88185983.txt
Build of product 'MyLambda' complete! (0.31s)
2025-01-29T12:44:48+0100 info LocalServer : host="127.0.0.1" port=7000 [AWSLambdaRuntime] Server started and listening

Then, from another Terminal, send your payload with curl. Note that the payload must be a valid JSON string. In the case of this function that accepts a simple String, it means the String must be wrapped in between double quotes.

curl -d '"seb"' http://127.0.0.1:7000/invoke    
"Hello seb"

Important

The local server is only available in DEBUG mode. It will not start with swift -c release run.

Build & Package

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

swift build
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/MyLambda/MyLambda.zip

Deploy

Here is how to deploy using the aws command line.

aws lambda create-function \
--function-name MyLambda \
--zip-file fileb://.build/plugins/AWSLambdaPackager/outputs/AWSLambdaPackager/MyLambda/MyLambda.zip \
--runtime provided.al2 \
--handler provided  \
--architectures arm64 \
--role arn:aws:iam::<YOUR_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 replace <YOUR_ACCOUNT_ID> 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 MyLambda \
--payload $(echo \"Seb\" | base64)  \
out.txt && cat out.txt && rm out.txt

Note that the payload is expected to be a valid JSON string, hence the surroundings quotes (").

This should output the following result.

{
    "StatusCode": 200,
    "ExecutedVersion": "$LATEST"
}
"Hello Seb"

Undeploy

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

aws lambda delete-function --function-name MyLambda