Refresher: serverless framework local development workflow

It’s been a while since I’ve written any notes about the Serverless framework, so here’s a few notes as a refresher on typical steps I use for local development.

As a reminder to self, regions I typically deploy to are:

  • us-west-1 : SF
  • us-west-2: Oregon
  • eu-west-2: London

AWS regions are listed here.

To deploy:

serverless deploy --region eu-west-2

To invoke local:

serverless invoke local --function functionName

To invoke remotely:

serverless invoke --function functionName --region eu-west-2

To check logs from last invoke:

serverless logs --function functionName --region eu-west-2

Using Serverless Framework to build and deploy Docker images for AWS Lambdas

AWS Lambdas can be packaged and deployed using a Docker image, described in the docs here.

Serverless Framework makes building and deploying a Docker based Lambda incredibly simple. If you have a simplest Dockerfile like this (from the docs here):


# Assumes your function is named "app.js", and there is a package.json file in the app directory 
COPY app.js package.json  ${LAMBDA_TASK_ROOT}

# Install NPM dependencies for function
RUN npm install

# Set the CMD to your handler (could also be done as a parameter override outside of the Dockerfile)
CMD [ "app.handler" ] 

The handler to be packaged in this image is this simplest hello world function:

exports.handler =  async function(event, context) {
    console.log("EVENT: \n" + JSON.stringify(event, null, 2))
    return "hello!"

To define a Lambda using this image, with Serverless define an ECR section like this to define your image, which will get built using the above Dockerfile in the same folder:

service: lambda-container-1

  name: aws
        path: ./

      name: lambda-container-example

Run ‘serverless deploy’ and it builds the image, uploads to ECR, and deploys the Lambda all for you.

After deploying, on first test I got this error:

  "errorMessage": "RequestId: 58fe500f-26ee-44ba-b6a9-6079b6ff2896 Error: fork/exec / exec format error",
  "errorType": "Runtime.InvalidEntrypoint"

The key part of this error is this “exec format error”. I’m building and deploying this from my M1 MacBook Pro, which is Apple’s arm64, not x64.

If we look in the AWS Console for this lambda, on the first page under Image you’ll see the Lambda runtime architecture:

Updating the serverless.yml to include ‘architecture: arm64’, redeploy and now the architecture is arm64:

Invoking with ‘serverless invoke –function hello’ and now it successfully runs!

Deploying changes to individual Lambdas using Serverless Framework

I have a serverless project that deploys 2 Lambdas in the same stack:

service: example-apis2

  name: aws
  memorySize: 512
  region: us-west-1
    restApiId: ${env:APIGWID} #  API Gateway to add this api to
    restApiRootResourceId: ${env:RESOURCEID}
    handler: index2.handler
      - arn:aws:lambda:us-west-1:[myaccountid]:layer:example-layer:1
      - http:
          path: api2
          method: get
    handler: index3.handler
      - arn:aws:lambda:us-west-1:[myaccountid]:layer:example-layer:1
      - http:
          path: api3
          method: get

After first deploy, if I do

aws lambda get-function --function-name example-apis2-dev-example2 
"LastModified": "2021-10-27T06:30:31.002+0000",


$ aws lambda get-function --function-name example-apis2-dev-example3
"LastModified": "2021-10-27T06:30:31.987+0000",

Now if I make a code change only to the example 3 Lambda and redeploy only that function with:

serverless deploy function -f example-apis2-dev-example3

… example2 has not been modified since the first deploy (same timestamp as the original deploy):

$ aws lambda get-function --function-name example-apis2-dev-example2
"LastModified": "2021-10-27T06:30:31.002+0000",,

and only example3 shows it was updated/redeployed:

$ aws lambda get-function --function-name example-apis2-dev-example3
"LastModified": "2021-10-27T06:33:17.736+0000",

serverless deploy : deploys the whole stack (but if nothing has changed there is no update)

serverless deploy function -f functioname: updates just the code on that one Lambda (and updates in a couple of seconds vs several seconds for updating the whole stack).

This is described in this article here.