Generate a mapping of AWS regions and availability zones for use in cloudformation

README

Generate a mapping of AWS regions and availability zones for use in cloudformation

example.yml

Mappings:
  # Output of the script.
  RegionsAndZones:
    ap-northeast-1: { a: true, b: false, c: true, d: true, e: false, f: false }
    ap-northeast-2: { a: true, b: false, c: true, d: false, e: false, f: false }
    ap-south-1: { a: true, b: true, c: false, d: false, e: false, f: false }
    ap-southeast-1: { a: true, b: true, c: true, d: false, e: false, f: false }
    ap-southeast-2: { a: true, b: true, c: true, d: false, e: false, f: false }
    ca-central-1: { a: true, b: true, c: false, d: false, e: false, f: false }
    eu-central-1: { a: true, b: true, c: true, d: false, e: false, f: false }
    eu-west-1: { a: true, b: true, c: true, d: false, e: false, f: false }
    eu-west-2: { a: true, b: true, c: true, d: false, e: false, f: false }
    eu-west-3: { a: true, b: true, c: true, d: false, e: false, f: false }
    sa-east-1: { a: true, b: false, c: true, d: false, e: false, f: false }
    us-east-1: { a: true, b: true, c: true, d: true, e: true, f: true }
    us-east-2: { a: true, b: true, c: true, d: false, e: false, f: false }
    us-west-1: { a: true, b: false, c: true, d: false, e: false, f: false }
    us-west-2: { a: true, b: true, c: true, d: false, e: false, f: false }

# Conditions to use the mapping in.
Conditions:
  ZoneAExists: !Equals [!FindInMap [RegionsAndZones, !Ref "AWS::Region", a], true]
  ZoneBExists: !Equals [!FindInMap [RegionsAndZones, !Ref "AWS::Region", b], true]
  ZoneCExists: !Equals [!FindInMap [RegionsAndZones, !Ref "AWS::Region", c], true]
  ZoneDExists: !Equals [!FindInMap [RegionsAndZones, !Ref "AWS::Region", d], true]
  ZoneEExists: !Equals [!FindInMap [RegionsAndZones, !Ref "AWS::Region", e], true]
  ZoneFExists: !Equals [!FindInMap [RegionsAndZones, !Ref "AWS::Region", f], true]

regionsandzones.sh

#!/usr/bin/env bash

set -eEuo pipefail

declare -A azs

read -ra regions <<<"$(aws ec2 describe-regions --query 'Regions[].RegionName|sort(@)' --output text)"

echo "RegionsAndZones:"
for region in "${regions[@]}"; do
    read -ra zones <<<"$(aws ec2 describe-availability-zones \
        --region "$region" \
        --query 'AvailabilityZones[].ZoneName' \
        --output text)"
    azs=()
    echo -n "  $region: { "
    for az in "${zones[@]#*[0-9]}"; do
        azs[$az]=true
    done
    for az in {a..f}; do
        echo -n "$az: ${azs[$az]:-false}, "
    done|head -c -2
    echo " }"
done