Using Troposphere to create CloudFormation stack template

If you’ve ever wrote AWS CloudFormation template, you probably know that it can be a daunting task. Luckily, it can be much easier, if you use Python’s library “Troposphere”.

Troposphere lets you create Python objects in place of CloudFormation elements, does some basic validation of your input and generates the JSON template for CloudFormation for you. It is much easier and cleaner to use that writing JSON templates manually.

To install troposphere, just run:

pip install troposphere

A very simple stack that creates a new VPC with private and public subnets in AZs A-C, can look like this:

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from troposphere import Ref, Template, Tags, Join
from troposphere.ec2 import VPC, Subnet, NetworkAcl, NetworkAclEntry, InternetGateway, \
VPCGatewayAttachment, RouteTable, Route, SubnetRouteTableAssociation, SubnetNetworkAclAssociation

VPC_NETWORK = "172.21.0.0/16"
VPC_PRIVATE_A = "172.21.1.0/24"
VPC_PRIVATE_B = "172.21.2.0/24"
VPC_PRIVATE_C = "172.21.3.0/24"
VPC_PUBLIC_A = "172.21.128.0/24"
VPC_PUBLIC_B = "172.21.129.0/24"
VPC_PUBLIC_C = "172.21.130.0/24"

t = Template()

t.add_description("Stack creating a VPC")

vpc = t.add_resource(VPC(
  "VPC",
  CidrBlock=VPC_NETWORK,
  InstanceTenancy="default",
  EnableDnsSupport=True,
  EnableDnsHostnames=False,
  Tags=Tags(
    Name=Ref("AWS::StackName")
  )
))

# internet gateway
internetGateway = t.add_resource(InternetGateway(
  "InternetGateway",
  Tags=Tags(
    Name=Join("", [Ref("AWS::StackName"), "-gateway"]),
  ),
))

gatewayAttachment = t.add_resource(VPCGatewayAttachment(
  "InternetGatewayAttachment",
  InternetGatewayId=Ref(internetGateway),
  VpcId=Ref(vpc)
))

# public routing table
publicRouteTable = t.add_resource(RouteTable(
  "PublicRouteTable",
  VpcId=Ref(vpc),
  Tags=Tags(
   Name=Join("-", [Ref("AWS::StackName"), "public-rt"]),
  ),
))

privateRouteTable = t.add_resource(RouteTable(
  "PrivateRouteTable",
  VpcId=Ref(vpc),
  Tags=Tags(
    Name=Join("-", [Ref("AWS::StackName"), "private-rt"]),
  ),
))

internetRoute = t.add_resource(Route(
  "RouteToInternet",
  DestinationCidrBlock="0.0.0.0/0",
  GatewayId=Ref(internetGateway),
  RouteTableId=Ref(publicRouteTable),
  DependsOn=gatewayAttachment.title
))

# private subnetworks
subnetPrivateA = t.add_resource(Subnet(
  "StackPrivateSubnetA",
  AvailabilityZone=Join("", [Ref("AWS::Region"), "a"]),
  CidrBlock=VPC_PRIVATE_A,
  MapPublicIpOnLaunch=False,
  Tags=Tags(
    Name=Join("", [Ref("AWS::StackName"), " private subnet A"]),
  ),
  VpcId=Ref(vpc)
))

t.add_resource(SubnetRouteTableAssociation(
  "PrivateSubnetARouteTable",
  RouteTableId=Ref(privateRouteTable),
  SubnetId=Ref(subnetPrivateA)
))

subnetPrivateB = t.add_resource(Subnet(
  "StackPrivateSubnetB",
  AvailabilityZone=Join("", [Ref("AWS::Region"), "b"]),
  CidrBlock=VPC_PRIVATE_B,
  MapPublicIpOnLaunch=False,
  Tags=Tags(
    Name=Join("", [Ref("AWS::StackName"), " private subnet B"]),
  ),
  VpcId=Ref(vpc)
))

t.add_resource(SubnetRouteTableAssociation(
  "PrivateSubnetBRouteTable",
  RouteTableId=Ref(privateRouteTable),
  SubnetId=Ref(subnetPrivateB)
))

subnetPrivateC = t.add_resource(Subnet(
  "StackPrivateSubnetC",
  AvailabilityZone=Join("", [Ref("AWS::Region"), "c"]),
  CidrBlock=VPC_PRIVATE_C,
  MapPublicIpOnLaunch=False,
  Tags=Tags(
    Name=Join("", [Ref("AWS::StackName"), " private subnet C"]),
  ),
  VpcId=Ref(vpc)
))

t.add_resource(SubnetRouteTableAssociation(
  "PrivateSubnetCRouteTable",
  RouteTableId=Ref(privateRouteTable),
  SubnetId=Ref(subnetPrivateC)
))

# public subnetworks
subnetPublicA = t.add_resource(Subnet(
  "StackPublicSubnetA",
  AvailabilityZone=Join("", [Ref("AWS::Region"), "a"]),
  CidrBlock=VPC_PUBLIC_A,
  MapPublicIpOnLaunch=True,
  Tags=Tags(
    Name=Join("", [Ref("AWS::StackName"), " public subnet A"]),
  ),
  VpcId=Ref(vpc),
))

t.add_resource(SubnetRouteTableAssociation(
  "PublicSubnetARouteTable",
  RouteTableId=Ref(publicRouteTable),
  SubnetId=Ref(subnetPublicA)
))

subnetPublicB = t.add_resource(Subnet(
  "StackPublicSubnetB",
  AvailabilityZone=Join("", [Ref("AWS::Region"), "b"]),
  CidrBlock=VPC_PUBLIC_B,
  MapPublicIpOnLaunch=True,
  Tags=Tags(
    Name=Join("", [Ref("AWS::StackName"), " public subnet B"]),
  ),
  VpcId=Ref(vpc),
))

t.add_resource(SubnetRouteTableAssociation(
  "PublicSubnetBRouteTable",
  RouteTableId=Ref(publicRouteTable),
  SubnetId=Ref(subnetPublicB)
))

subnetPublicC = t.add_resource(Subnet(
  "StackPublicSubnetC",
  AvailabilityZone=Join("", [Ref("AWS::Region"), "c"]),
  CidrBlock=VPC_PUBLIC_C,
  MapPublicIpOnLaunch=True,
  Tags=Tags(
    Name=Join("", [Ref("AWS::StackName"), " public subnet C"]),
  ),
  VpcId=Ref(vpc)
))

t.add_resource(SubnetRouteTableAssociation(
  "PublicSubnetCRouteTable",
  RouteTableId=Ref(publicRouteTable),
  SubnetId=Ref(subnetPublicC)
))

# network ACL for private subnets
privateNetworkAcl = t.add_resource(NetworkAcl(
  "PrivateNetworkAcl",
  VpcId=Ref(vpc),
  Tags=Tags(
    Name=Join("", [Ref("AWS::StackName"), "-private-nacl"]),
  ),
))

t.add_resource(SubnetNetworkAclAssociation(
  "PrivateNetworkAAclAss",
  SubnetId=Ref(subnetPrivateA),
  NetworkAclId=Ref(privateNetworkAcl)
))

t.add_resource(SubnetNetworkAclAssociation(
  "PrivateNetworkBAclAss",
  SubnetId=Ref(subnetPrivateB),
  NetworkAclId=Ref(privateNetworkAcl)
))

t.add_resource(SubnetNetworkAclAssociation(
  "PrivateNetworkCAclAss",
  SubnetId=Ref(subnetPrivateC),
  NetworkAclId=Ref(privateNetworkAcl)
))

t.add_resource(NetworkAclEntry(
  "PrivateNetworkAclEntryIngress",
  CidrBlock=VPC_NETWORK,
  Egress=False,
  NetworkAclId=Ref(privateNetworkAcl),
  Protocol=-1,
  RuleAction="allow",
  RuleNumber=200
))

t.add_resource(NetworkAclEntry(
  "PrivateNetworkAclEntryEgress",
  CidrBlock=VPC_NETWORK,
  Egress=True,
  NetworkAclId=Ref(privateNetworkAcl),
  Protocol=-1,
  RuleAction="allow",
  RuleNumber=200
))

print(t.to_json())

Save this as vpc_stack.py and run python vpc_stack.py. Output will be a JSON template that can be used for CloudFormation!

You can easily direct the output to a file, by running python vpc_stack.py > vpc_stack.json. The JSON file can be uploaded directly to CloudFormation via CLI or AWS Management Console.

To find out more and for full documentation, see troposphere on github: https://github.com/cloudtools/troposphere.

For more examples of CloudFormation stacks with troposphere, check out our github repo: https://github.com/MysteriousCode/cloudformation-examples.

Using Troposphere to create CloudFormation stack template

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