Serverless Selective Functions

A Serverless plugin that enables you to selectively deploy functions for specific stages.

Installation

npm i @govtechsg/serverless-selective-functions --save-dev

Add the plugin to your serverless.yml file:

plugins:
  - "@govtechsg/serverless-selective-functions"

Usage

# Everything included by default
addVote:
  handler: src/functionHandlers/addVote/index.handler
  events:
    - http:
        path: /v1/vote
        method: post
        cors: true
  # Not specifying the `stages` property will include this function

# Exclude all prod-[0-9]*
deleteVote:
  handler: src/functionHandlers/deleteVote/index.handler
  events:
    - http:
        path: /v1/vote
        method: delete
        cors: true
  stages:
    exclude: # Specify stages that should exclude this function
      - "prod-[0-9]*" # Regex

# Include all dev-.* except dev-123
# Note that checks will run through the inclusion list first, then the exclusion list
editVote:
  handler: src/functionHandlers/editVote/index.handler
  events:
    - http:
        path: /v1/vote
        method: patch
        cors: true
  stages: # Stage will be tested with both the include and exclude properties
    include:
      - "dev-.*"
    exclude:
      - "dev-123"

# Include dev-123 and all prod-.*
summary:
  handler: src/functionHandlers/summary/index.handler
  events:
    - http:
        path: /v1/summary
        method: get
        cors: true
  stages:
    include:
      - "dev-123"
      - "prod-.*"

Why?

You may want to deploy some functions as specified in your serverless.yml only for a specific stage. A simple approach would be the following:

functions:
  - ${file(serverless/functions/base.yml)}
  - ${file(serverless/functions/${self:provider.stage}.yml)}

Then if you wanted to deploy functions only when the stage is set to offline, you can create a serverless/functions/offline.yml file and populate it with functions meant only for the offline stage.

The approach works for simple cases, but lets say you want to deploy the following functions for 3 stages:

prod: lambdaA, lambdaB
staging: lambdaB
offline: lambdaA, lambdaC

Given that there isn't a common subset of functions, you cannot create a base.yml. If you create a prod.yml with lambdaA + lambdaB, and staging.yml with lambdaB, you will then need to maintain 2 separate definitions of lambdaB which would be error prone. This restricts you to having mutually exclusive sets of functions defined in different yml files, otherwise we tradeoff maintainability.