handle Serverless provisioning from Terraform

conditional-removal.sh

#!/bin/bash

# $1 is the name of the repository
# $2 is the optional tag of the repository

REMOVE=$(node should-remove.js microservice)
if [[ $REMOVE == "true" ]]; then
  git clone https://github.com/owner/$1.git
  cd $1/
  if [ "$2" != "" ]; then
    git checkout tags/$2 -b $2
  fi
  yarn install
  yarn serverless remove
  cd ..
  rm -rf $1/
fi

deploy.sh

#!/bin/bash

# $1 is the name of the repository
# $2 is the optional tag of the repository

git clone https://github.com/owner/$1.git
cd $1/
if [ "$2" != "" ]; then
  git checkout tags/$2 -b $2
fi
yarn install
yarn serverless deploy
cd ..
rm -rf $1/

main.tf

...
locals { microservice_version = "v1.9.0" }
resource "null_resource" "microservice" {
  # either do not define count or set count = 0 for soft deletion
  depends_on = [null_resource.some_other_resource]
  triggers   = { version = "${local.microservice_version}" }
  provisioner "local-exec" {
    # deploy from serverless
    command     = "bash deploy.sh microservice ${local.microservice_version}"
    # required environment variables
    environment = { ... }
  }
  provisioner "local-exec" {
    # deploy from serverless
    command     = "bash conditional-removal.sh microservice ${local.microservice_version}"
    when        = destroy
    # required environment variables
    environment = { ... }
  }
}

should-remove.js

const fs = require('fs')
const path = require('path')
const hcltojson = require('hcl-to-json')
const config = fs.readFileSync(path.join(__dirname, 'main.tf'), { encoding: 'utf8' })

// $1 is the name of the repository
const [repo] = process.argv.slice(2)

const { resource } = hcltojson(config)
const { null_resource } = resource
const definition = null_resource[repo]
const count = definition.hasOwnProperty('count') ? definition.count : 1

// not marked for deletion
if (count === 1) console.log(false)
// count should either be undefined or set to 0
else if (count > 1) throw new Error('this script cannot handle multiple count of the same null_resource')
// has been marked for deletion
else console.log(true)

It's worth mentioning that any change to null_resource definition will trigger the destroy-time provisioner, but we might not want serverless remove to be run on each change, except if count = 0 or if the resource it depends_on has been deleted, hence this workaround to handle conditional-removal.

As a side note it seems possible to handle multiple count on the null_resource by introspecting both terraform.tfstate and terraform.tfstate.backup and guessing which one have been added, deleted or had its version updated.

Also it's probably possible to do everything in bash in case we don't want to rely on JavaScript for files parsing purpose, but that might require hardcore awk commands or installing additional package like jq (which then would require additional scripts / packages work to work on platforms other than Linux).

A better alternative would be to create a Terraform Module to handle all this automatically, but it's far beyond my sample purpose :)

Sadly I tested to create a Terraform module locally but even if the script currently executes and does the job, this way is clearly stated as deprecated and might stop to work in future versions of Terraform.

My current version is :

Terraform v0.12.19
+ provider.null v2.1.2

whether using variables.tf :

or piping them through environment :