Script to create a change set against a stack and execute it if it is exclusively Tags in scope

create-tags-change-set.sh

#!/bin/bash
set -e
set -o pipefail
set -u

# depends on cfparams: https://github.com/cultureamp/cfparams

FARM=$1

CHANGE_SET_NAME="changeset-tags-$(date +%Y%m%d%H%M%S)-$(git rev-parse HEAD)"
STACK_NAME="$FARM-influx-db"

main() {
  echo "[>] Creating change set"
  create_change_set
  echo "[+] Change set created"
  local status; status="$(check_change_set)"

  case $status in
    "EMPTY")
      echo "[+] Empty change set created"
      delete_change_set
      echo "[+] Change set discarded"
      exit 0
      ;;

    "TAGS")
      echo "[+] Change set contains ONLY 'Tags' scope"
      execute_change_set
      echo "[+] Stack update complete!"
      exit 0
      ;;
    
    "FAILED")
      echo "[!] Change set creation failed for a reason other than being empty"
      exit 1
      ;;

    "OTHER")
      echo "[!] Change set contains scopes other than 'Tags' -- not executing"
      exit 1
      ;;

    *)
      echo "[!] Unknown change set status -- not executing"
      exit 1
  esac
}

get_current_parameters() {
  aws cloudformation get-template --stack-name="$STACK_NAME" | yq -P .TemplateBody > "stack-${CHANGE_SET_NAME}.json"
  cfparams --template "stack-${CHANGE_SET_NAME}.json"
  rm "stack-${CHANGE_SET_NAME}.json"
}

get_tags() {
  cat "tags-$FARM.json"
}

get_change_set() {
  aws cloudformation describe-change-set \
    --stack-name "${STACK_NAME}" \
    --change-set-name "${CHANGE_SET_NAME}"
}

create_change_set() {
  aws cloudformation create-change-set \
    --stack-name="$STACK_NAME" \
    --capabilities=CAPABILITY_IAM \
    --use-previous-template \
    --parameters="$(get_current_parameters)" \
    --tags="$(get_tags)" \
    --change-set-name="$CHANGE_SET_NAME" \
    --query=Id --output=text

  aws cloudformation wait change-set-create-complete \
    --stack-name="$STACK_NAME" \
    --change-set-name="$CHANGE_SET_NAME" || echo "[!] Continuing..."
}

check_change_set() {
  local change_set; change_set="$(get_change_set)"
  local is_failed; is_failed=$(echo $change_set | jq '.Status == "FAILED"')

  if [ $is_failed = "true" ]; then
    local empty_status_reason; empty_status_reason="The submitted information didn't contain changes. Submit different information to create a change set."
    local is_empty; is_empty=$(echo $change_set | jq ".StatusReason == \"$empty_status_reason\"")
    if [ $is_empty = "true" ]; then
      echo "EMPTY"
    else
      echo "FAILED"
    fi
  else
    local is_tags; is_tags=$(echo $change_set | jq '[.Changes[].ResourceChange.Scope] | flatten | [.[] == "Tags"] | all')
    if [ $is_tags = "true" ]; then
      echo "TAGS"
    else
      echo "OTHER"
    fi
  fi
}

execute_change_set() {
  echo "[>] Executing change set"
  aws cloudformation execute-change-set \
    --stack-name "${STACK_NAME}" \
    --change-set-name "${CHANGE_SET_NAME}"

  echo "[>] Waiting for stack update"
  aws cloudformation wait stack-update-complete \
    --stack-name "${STACK_NAME}"
}

delete_change_set() {
  echo "[>] Deleting change set"
  aws cloudformation delete-change-set \
    --stack-name "${STACK_NAME}" \
    --change-set-name "${CHANGE_SET_NAME}"
}

main "$@"