SAM Template Creator

Intro

The SAM Template Creator helps you set up Infrastructure as Code for an AWS serverless project. It reads your project folder and generates a SAM template containing the necessary functions, globals, environment variables, etc.

Compared to a full-fledged framework like Serverless, the scope of this template creator is limited. But this has advantages as well: the tool is lightweight, generating no additional files except your IaC yaml, and is simple to use. Though it may not suffice for very complex use-cases, it can still provide a starting point to expand upon.

Requirements

• python 3.5 or higher
• pip
• a serverless project to scan. Currently only Python and Go projects are supported. Support for Node and Java is planned.

Usage Guide / How-to

Install the tool using pip

pip install sam-template-creator

# or alternatively

pip3 install sam-template-creator

Now either go to the root directory of your project and type

sam-template-creator --location .

# or with shorthand argument names

sam-template-creator -l .

Or use an absolute path from any directory

sam-template-creator --location /path/to/project

The script will create a template.yaml file in the root of your project's directory. Check its contents! It might point out some things you have to fill in. If a file with that name already exists, a backup will be created. If the pre-existing file is a SAM template, the tool will try to use it to fill in values of the new template.

You can also pass some (optional) arguments:

• language: by default, the tool will guess which language the project is written in. If it does not find the correct language, or if you want an older version of the runtime (the script will default to the latest version), you can use this argument.
• globals: if used, the memory and timeout of the lambdas will be set globally, instead of per function

With your template created, you should now be able to deploy to AWS using

aws cloudformation package --template-file template.yaml --s3-bucket YOUR-BUCKET-NAME --output-template-file outputSamTemplate.yaml
aws cloudformation deploy --template-file outputSamTemplate.yaml --stack-name PICK-A-STACK-NAME --capabilities CAPABILITY_IAM

Notes on usage

Important! SAM Template Creator requires your project to be organised in a certain way.

Directory

The tool will work best if every lambda has its own directory, though it should be able to handle other project structures as well.
The file containing the handler and files it directly refers to will be checked for information on required permissions, environment variables, etc.

If a single zip (for most languages) or executable is present in the folder of the handler file, or a subfolder, the tool assumes this zip contains the code you want to upload.

Naming conventions

Python

• the name of the Lambda handler function should contain the word 'handler'. The event should end with 'event' and the context should be 'context'. For example def lambda_handler(s3event, context)
• if part of the name equals a http method, we assume you want to map it to an api gateway method with the path represented by the rest of the name. For example, if your handler's name is def put_hello_world_hander(event, context), the function is mapped to a PUT to /hello/world.
• if the lambda is triggered by an event source, the name should reflect this. For example, if s3 is the source, the name of the event should contain s3: s3event or s3_event or... If you want a cron event, you can name the event 5_hours_event or similar and an event that runs every 5 hours will be created.

Go

• the name of your executable should be handler, except if you have an executable in the folder of your lambda, called main. If so, the tool will assume that this executable has the code of your lambda. It will set Handler and CodeUri accordingly.
  For example, if your folder mylambda contains a main file under dist/main, the Handler will become main, with the CodeUri equal to /mylambda/dist/main.
• if you want to map a function to an api gateway method, the lambda handler should end with the word Request, with the path and method prepended to this word. For example, func PostAddHelloRequest(_ context.Context, event events.APIGatewayProxyRequest) error is mapped to a POST to /add/hello.
• if the lambda is triggered by an event source, the name should reflect that. For example, if s3 is the source, the name of the event should contain s3, like this: s3event or s3_event or... If you want a cron event, you can name the event 5_hours_event or similar and an event that runs every 5 hours will automatically be created.

Node

• TODO

Java

• TODO

Project Structure

There are three main parts to this project

• reader: contains files that help with reading the files in the project. The FileInfo.py class reads an individual file and retrieves resources and other configuration information. Because files will look very different depending on the language, it uses the strategy pattern to aid in these language-specific tasks. For example, when dealing with Python, the PythonStrategy class is used.
• middleware: these files and functions take the information from the read side and do transforms, adding/removing certain config, before this is passed to the writers.
• writer: these files are responsible for writing the information to yaml.

Besides these folders, there is a util folder, the coordinator.py file which coordinates the work of the other files and the command_line.py, which contains the argument parser and calls the coordinator after checking the input.

Tests

Unit tests can be run with python -m unittest. A relatively simple it-test is run with the bash script test.sh under tests/it-test. It requires a bucket as argument (for uploading the lambda zip) and default AWS credentials.

Releases

Releases on pip might be behind a bit on the latest commits to the project.

Roadmap

• Solve TODO's
• More use of previous template values
• Multiple sns/sqs/... events (by prefix of name?)
• Step function support (by name of event and return value?)
• Languages
  • Node
  • Java
• Robust error handling
• Ask questions. Call dynamo -> add to template? Sns publish -> add a topic?
• More general questions (generate outputs, deploy template,...)?
• More flexibility in location of lambdas: searching more folders, or ability to specify folder structure?
• Polyglot projects?