jg75 / aws-lambdas

Dump useful functions here

AWS Lambdas

Topics

• Cloudformation Integrations
  1. Custom Resources
  2. Custom Resource Handler
  3. Basic Calculator Handler
  4. Network Calculator Handler

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CloudFormation Integrations

Custom Resources

For information about custom resources, refer to the Documentation.

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Custom Resource Handler

Base class for lambda backend for CloudFormation custom resources provides methods for parsing the event object, sending a response to cloudformation, and returning a well formed response. An overridable method execute, which can be implemented by derived classes performs the Operation on a list of Operands. A dictionary operations used as a registry of Operator to function mappings used by this handler.

Given the following template:

Parameters:
  MyCustomResourceFunction:
    Description: Custom resource handler function Arn
    Type: AWS::SSM::Parameter::Value<String>
    Default: /MyCommonFunctions/MyCustomResourceFunction

Resources:
  MyEcho:
    Type: Custom::Echo
    Properties:
      ServiceToken: !Ref MyCustomResourceFunction
      Operator: echo
      Operands:
        - this is a
        - test

Outputs:
  Echo:
    Description: The output of the custom resource
    Value: !GetAtt MyEcho.Value

The following will be included in the lambda event:

{
    'ResponseURL': 'http://pre-signed-S3-url-for-response',
    'StackId' : 'arn:aws:cloudformation:us-west-2:123456789012:stack/stack-name/guid',
    'RequestId' : 'unique id for this create request',
    'ResourceType' : 'Custom::Echo',
    'LogicalResourceId' : 'MyEcho',
    'ResourceProperties': {
        'Operator': 'echo',
        'Operands': ['this is a', 'test']
    }
}

The Data response data of the execute method is put into a dictionary as a string:

{
    'Value': str(operations[operator](operands))
}

The Status is captured as a string 'SUCCESS' | 'FAILED'.

The following payload will be sent to the ResponseUrl for cloudformation:

{
{
    'Status': 'SUCCESS' or 'FAILED',
    'LogStream': context.log_stream_name,
    "PhysicalResourceId": pysical_resource_id or context.log_stream_name,
    'StackId': event['StackId'],
    'RequestId': event['RequestId'],
    'LogicalResourceId': event['LogicalResourceId'],
    'NoEcho': True | False,
    'Data': data
}
}

The following responses are returned by the handler.

Success response:

{
    statusCode: 200,
    body: <json data>
}

Failed response:

{
    statusCode: 400,
    body: <json data with the exception>
}

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Basic Calculator Handler

Lambda backend for CloudFormation custom resources providing basic calculator functions.

Operations:

• /
• %

Operands:

• Number(s)

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Network Calculator Handler

Lambda backend for CloudFormation custom resources that do networking related caclulations like the subnet size in bits of a given network cidr for a specific number of subnets.

Operations:

• SubnetSize

Operands:

• CIDR
• Number of subnets

aws-lambdas's Issues

Missing Tests

Needs documentation

cfnresponse is deprecated

you should do something about that

It'd be a lot cooler if you did CI/CD