Getting Started with AWS Lambda in Pulumi

For a small research project of mine, I needed to create HTTP triggered AWS Lambda’s in all supported programming languages.

I’m not a power AWS user, so I get easily confused about the configuration of things like IAM roles or API Gateway. Moreover, I wanted my environment to be reproducible, so manual AWS Console wasn’t a good option.

I decided it was a good job for Pulumi. They pay a lot of attention to serverless and especially AWS Lambda, and I love the power of configuration as code.

I created a Pulumi program which provisions Lambda’s running on Javascript, .NET, Python, Java and Go. Pulumi program itself is written in Javascript.

I’m describing the resulting code below in case folks need to do the same thing. The code itself is on my github.

Javascript

Probably, the vast majority of Pulumi + AWS Lambda users will be using Javascript as programming language for their serverless functions.

No wonder that this scenario is the easiest to start with. There is a high-level package @pulumi/cloud-aws which hides all the AWS machinery from a developer.

The simplest function will consist of just several lines:

const cloud = require("@pulumi/cloud-aws");

const api = new cloud.API("aws-hellolambda-js");
api.get("/js", (req, res) => {
    res.status(200).json("Hi from Javascript lambda");
});

exports.endpointJs = api.publish().url;

Configure your Pulumi stack, run pulumi update and a Lambda is up, running and accessible via HTTP.

.NET Core

.NET is my default development environment and AWS Lambda supports .NET Core as execution runtime.

Pulumi program is still Javascript, so it can’t mix C# code in. Thus, the setup looks like this:

• There is a .NET Core 2.0 application written in C# and utilizing Amazon.Lambda.* NuGet packages
• I build and publish this application with dotnet CLI
• Pulumi then utilizes the published binaries to create deployment artifacts

C# function looks like this:

public class Functions
{
    public async Task<APIGatewayProxyResponse> GetAsync(APIGatewayProxyRequest request, ILambdaContext context)
    {
        return new APIGatewayProxyResponse
        {
            StatusCode = (int)HttpStatusCode.OK,
            Body = "\"Hi from C# Lambda\"",
            Headers = new Dictionary<string, string> { { "Content-Type", "application/json" } }
        };
    }
}

For non-Javascript lambdas I utilize @pulumi/aws package. It’s of lower level than @pulumi/cloud-aws, so I had to setup IAM first:

const aws = require("@pulumi/aws");

const policy = {
    "Version": "2012-10-17",
    "Statement": [
        {
            "Action": "sts:AssumeRole",
            "Principal": {
                "Service": "lambda.amazonaws.com",
            },
            "Effect": "Allow",
            "Sid": "",
        },
    ],
};
const role = new aws.iam.Role("precompiled-lambda-role", {
    assumeRolePolicy: JSON.stringify(policy),
});

And then I did a raw definition of AWS Lambda:

const pulumi = require("@pulumi/pulumi");

const csharpLambda = new aws.lambda.Function("aws-hellolambda-csharp", {
    runtime: aws.lambda.DotnetCore2d0Runtime,
    code: new pulumi.asset.AssetArchive({
        ".": new pulumi.asset.FileArchive("./csharp/bin/Debug/netcoreapp2.0/publish"),
    }),
    timeout: 5,
    handler: "app::app.Functions::GetAsync",
    role: role.arn
});

Note the path to publish folder, which should match the path created by dotnet publish, and the handler name matching C# class/method.

Finally, I used @pulumi/aws-serverless to define API Gateway endpoint for the lambda:

const serverless = require("@pulumi/aws-serverless");

const precompiledApi = new serverless.apigateway.API("aws-hellolambda-precompiledapi", {
    routes: [
        { method: "GET", path: "/csharp", handler: csharpLambda },
    ],
});

That’s definitely more ceremony compared to Javascript version. But hey, it’s code, so if you find yourself repeating the same code, go ahead and make a higher order component out of it, incapsulating the repetitive logic.

Python

Pulumi supports Python as scripting language, but I’m sticking to Javascript for uniform experience.

In this case, the flow is similar to .NET but simpler: no compilation step is required. Just define a handler.py:

def handler(event, context): 
    return {
        'statusCode': 200,
        'headers': {'Content-Type': 'application/json'},
        'body': '"Hi from Python lambda"'
    }

and package it into zip in AWS lambda definition:

const pythonLambda = new aws.lambda.Function("aws-hellolambda-python", {
    runtime: aws.lambda.Python3d6Runtime,
    code: new pulumi.asset.AssetArchive({
        ".": new pulumi.asset.FileArchive("./python"),
    }),
    timeout: 5,
    handler: "handler.handler",
    role: role.arn
});

I’m reusing the role definition from above. The API definition will also be the same as for .NET.

Go

Golang is a compiled language, so the approach is similar to .NET: write code, build, reference the built artifact from Pulumi.

My Go function looks like this:

func Handler(request events.APIGatewayProxyRequest) (events.APIGatewayProxyResponse, error) {

 return events.APIGatewayProxyResponse{
  Body:       "\"Hi from Golang lambda\"",
  StatusCode: 200,
 }, nil

}

Because I’m on Windows but AWS Lambda runs on Linux, I had to use build-lambda-zip tool to make the package compatible. Here is the PowerShell build script:

$env:GOOS = "linux"
$env:GOARCH = "amd64"
go build -o main main.go
~\Go\bin\build-lambda-zip.exe -o main.zip main

and Pulumi function definition:

const golangLambda = new aws.lambda.Function("aws-hellolambda-golang", {
    runtime: aws.lambda.Go1dxRuntime,
    code: new pulumi.asset.FileArchive("./go/main.zip"),
    timeout: 5,
    handler: "main",
    role: role.arn
});

Java

Java class implements an interface from AWS SDK:

public class Hello implements RequestStreamHandler {

    public void handleRequest(InputStream inputStream, OutputStream outputStream, Context context) throws IOException {

        JSONObject responseJson = new JSONObject();

        responseJson.put("isBase64Encoded", false);
        responseJson.put("statusCode", "200");
        responseJson.put("body", "\"Hi from Java lambda\"");  

        OutputStreamWriter writer = new OutputStreamWriter(outputStream, "UTF-8");
        writer.write(responseJson.toJSONString());  
        writer.close();
    }
}

I compiled this code with Maven (mvn package), which produced a jar file. AWS Lambda accepts jar directly, but Pulumi’s FileArchive is unfortunately crashing on trying to read it.

As a workaround, I had to define a zip file with jar placed inside lib folder:

const javaLambda = new aws.lambda.Function("aws-coldstart-java", {
    code: new pulumi.asset.AssetArchive({
        "lib/lambda-java-example-1.0-SNAPSHOT.jar": new pulumi.asset.FileAsset("./java/target/lambda-java-example-1.0-SNAPSHOT.jar"),
    }),
    runtime: aws.lambda.Java8Runtime,
    timeout: 5,
    handler: "example.Hello",
    role: role.arn
});

Conclusion

The complete code for 5 lambda functions in 5 different programming languages can be found in my github repository.

Running pulumi update provisions 25 AWS resources in a matter of 1 minute, so I can start playing with my test lambdas in no time.

And the best part: when I don’t need them anymore, I run pulumi destroy and my AWS Console is clean again!

Happy serverless moments!