Lambda smush py

Utility with the sole aim to squeeze that little bit more code out of Python based AWS Lambda functions defined in-line to CloudFormation templates.

• How it works
• Usage
• Examples

How it works

CloudFormation offers the ability to define Lambda function code directly within templates for Python and Node.js runtimes via the Code: property - negating the need for an S3 code bucket and great for keeping smaller functions tightly coupled with a stack.

Unfortunately the allowed code size - including whitespace, is limited to 4096 characters. With this utility a Python based Lambda function is transformed to a compressed equivalent which is inflated at runtime to gain additional kilobytes of usable space for in-lined functions.

At time of invoke the following steps are executed:

• Temporary file created within the Lambda container.
• File populated with Base64 decoded and inflated function source.
• Python then loads the source as a new module (imp.load_source()).
• Proxy function acting as the handler then calls module handler, executing the original source.
• Additional function invokes for the lifetime of the container will simply call the proxy function - the decode and inflate steps only occur once, adding very little additional overhead.

The bootloader ends up being nothing more than:

import base64,imp,tempfile,zlib
_='''\
SOURCE_FUNCTION_BASE64_ENCODED_AND_COMPRESSED\
'''
l=tempfile.mkdtemp()+'/l.py'
h=open(l,'w')
h.write(zlib.decompress(base64.b64decode(_)))
h.close()
m=imp.load_source('l',l)
def HANDLER_NAME(e,c):
	return m.HANDLER_NAME(e,c)

Usage

usage: lambdasmushpy.py [-h] --source SOURCE --handler-name HANDLER_NAME
                        [--strip-comments] [--strip-empty-lines]
                        [--template YAML] [--template-placeholder PLACEHOLDER]
                        [--output FILE]

Generates compressed Python based AWS Lambda functions designed to fit within
the 4096 byte in-line limit of a CloudFormation template

optional arguments:
  -h, --help            show this help message and exit
  --source SOURCE       path to Lambda function
  --handler-name HANDLER_NAME
                        name of handler Lambda calls to invoke function
  --strip-comments      remove comment only lines to further reduce function
                        size
  --strip-empty-lines   remove empty lines to further reduce function size
  --template YAML       merge generated code into given YAML CloudFormation
                        template
  --template-placeholder PLACEHOLDER
                        place holder text within CloudFormation template
  --output FILE         write output to given filename, otherwise send to
                        console

Examples

Source function /path/to/lambda.py with handler my_handler() is compressed, with the result sent to console:

$ ./lambdasmushpy.py" \
	--source "/path/to/lambda.py" \
	--handler-name "my_handler"

Generated functions can also be embedded directly into CloudFormation YAML templates through the use of a placeholder.

For this example the compressed source is further reduced by removing comment and empty lines, the final embedded result is written to /path/to/final/template.yaml:

$ ./lambdasmushpy.py" \
	--source "/path/to/lambda.py" \
	--handler-name "my_handler" \
	--strip-comments \
	--strip-empty-lines \
	--template "/path/to/source/template.yaml" \
	--template-placeholder SMUSH_FUNCTION \
	--output "/path/to/final/template.yaml"

The bundled example/ shows this process end-to-end in detail.