NodeJS Lambda Debugger

WHAT IS IT

A generic JS/Typescript dev tool that enables digging into and debugging deployed AWS lambdas by delegating their execution to a local machine.

HOW DOES IT WORK

• Deployment phase Should be done once per account+region to:
  • allocate a dynamoDB table used for caching and act as an event ledger
  • Create a lambda layer that, once applied to a lambda during a debugging session, mirrors the trigger event to the local machine
• Connection phase Executing in any IDE debugger terminal the 'connect' CLI command will:
  • Map the relevant lambdas (either manually provided or auto-discovered from a given cloudformation template)
  • Update the remote lambdas to mirror the trigger event when the local machine is in active debugging

PREREQUISITES

• Programmatic access to an AWS account containing a Lambda with code that can be executed on a local machine.

HOW TO INSTALL

• Install : npm i -g diger ts-node typescript
• Deploy : diger deploy (once per account+region. use '-h' to override default params)  example: diger deploy -p aws-dev-account -r eu-central-1

HOW TO USE

• From a project's root path, execute in your IDE's debug terminal: diger connect (use '-h' for override options)

• diger connect defaults:

  • use the local machine's default AWS profile+region
  • Auto-discover and map the lambdas in a Cloudformation template located at the the project's root at template.yml
  • Bind to handler files located at the paths described in the template.yml

• diger connect overrides:

  • -p <aws-profile>  override the default profile aws uses
  • -r <aws-region>  override the default region aws uses
  • -s <stack-name>  name of the stack that containing lambdas to debug
  • -t <template-path>  path to the local Cloudformation template. Default: ./template.yml
  • -u <code-uri>  enforce a different base path to all lambda handlers.   Default: CodeUri defined in template.yml    example: '-u ./build/'.
  • -m <manual-mapping>  override the template's mapping relative path to a file manually mapping lambdas to their local handlers.   Example: examples/mapping.js`, null)
  • -v  enable verbose logging to print runtime execution and events IO
  • -u <code-uri>  override all handlers base path (lambda CodeUri)
  • -v <verbose>  print execution logs
  • -c <clean-logs>  erase previously stored queued trigger events before starting a new debug session
  • -f <config-file>  path to a diger config file storing the overrides and manual lambda mapping. Run 'diger generate-config-file to generate an example file
  • -n <diger-stack-Name>  override the default name for diger resources stack. Default: diger

HOW TO REMOVE

• If you wish to update the lambdas or when debugging is no longer needed, execute diger detach for that specific stack/lambda

GOOD TO KNOW

• Debugging a single lambda that is not part of a cloudformation stack can be debugged by generating a diger config file and mapping the lambda name to the local handler file, keeping the stackName field empty.
• For TS projects, if during execution node throws a "Cannot find module" error, try resolving the paths by:
  • execute npm i -D tsconfig-paths
  • adding to the project's tsconfig.json file: "ts-node": {"require": ["tsconfig-paths/register"]}
• When local handler code is executed, it's allocated with the envVars of their Cloud counterpart. This enables the code to interact with the stack's resources.
• During debugging, handlers are resolved and triggered based on the path defined in the service's template file (support both js and typescript). If the local path is different to what is defined in the Cloudformation stack, generate an diger config file and override the paths.
• Local handler scripts are loaded only when triggered. Changing code takes effect immediatly. Restarting diger is not needed.

CLI EXAMPLES

• Initial deployment:  diger deploy -p aws-dev-account -r eu-central-1
• Stack debugging:  diger connect -p aws-dev-account -r eu-central-1 -s my-test-stack
• Detach diger from the stack:  diger detach -p aws-dev-account -r eu-central-1
• Stack debugging with local handler path prefix override:  diger connect -p aws-dev-account -r eu-central-1 -s my-test-stack -u ./build
• Using a project config file:  create: diger generate-config-file -p diger.config.js  connect: diger deploy -f diger.config.js diger