aws sam in 30 seconds

Preamble: I am exploring different areas of AWS and am finding the jargon overwhelming. To help myself, I’ll be writing up summaries of some of the different services I come across, what they are, some core concepts, and links to resources for future reference.

All entries in the series are tagged with aws in 30 seconds and can be found here.

SAM is a CLI for AWS. The acronym stands for Serverless Application Model and as the name suggests, it’s more than just writing lambdas locally. It’s a suite of tools for writing entire applications. From the “What is AWS SAM” documentation:

A serverless application is a combination of Lambda functions, event sources, and other resources that work together to perform tasks. Note that a serverless application is more than just a Lambda function—it can include additional resources such as APIs, databases, and event source mappings.

SAM uses CloudFormation which allows for consistent, automated deployments.

Key Features

1. Bootstrap with a template

   sam init

   Invoking init will walk through an interactive set of prompts. Using these, it’s possible to get up and running using a set of blue prints for different types of apps (from the basic helloWorld to more complex ones using S3, SNS, SQS, or even as a web backend. )

2. Test locally

   If you have Docker installed, you can run the entire application locally on port 3000 (default) with:

   sam local start-api

   Alternatively, you can test single invocations. The simplest way to do this is to call invoke from within the application directory:

   sam local invoke

   You can specify what you want to invoke as well:

   sam local invoke "HelloWorldFunction" -e events/event.json

   This invocation will pick up the test event in the events directory, event.json. Alternatively, you can pass in your own events at the time of invocation:

   sam local generate-event apigateway aws-proxy --body "" --path "hello" --method GET > api-event.json
   diff events/api-event.json event/sevent.json

3. Guided deployments

   One of the big advantages to using SAM is that the infrastructure is all spelled out in the template.yml.

   Because of that deployments are automated and you can verify your changes before pushing them up.