Run bash script when Stack Created - amazon-web-services

Question

I'm designing an AWS stack that contains multiple instances that run a handful of services comprised of a few tasks each. One of these services uses NFS to store configuration, and this configuration needs to be setup ONCE when the stack is created.
I've come up with a way to run a configuration script ONCE when the stack is created:
Configure the service that needs to configure itself to run a single task
When the task starts, check if the configuration exists. If it doesn't, run a configuration script and then update the desired task count so that other instances are created
(1) is necessary to avoid a race condition.
Although this works well, it strikes me as a very round-about way to achieve something simple: run a bash script ONCE when my stack is created. Is there a better way to do this?

Answer 1

You can run a one-off Bash script using an AWS::EC2::Instance resource with an InstanceInitiatedShutdownBehavior property of terminate (to terminate the instance after the script executes), and a DependsOn attribute set to the last-created resource in your stack (so the EC2 instance gets created and the Bash script gets executed at the end):
Description: Run a bash script once when a stack is created.
Mappings:
# amzn-ami-hvm-2016.09.1.20161221-x86_64-gp2
RegionMap:
us-east-1:
"64": "ami-9be6f38c"
Resources:
MyResource:
Type: AWS::SNS::Topic
WebServer:
Type: AWS::EC2::Instance
DependsOn: MyResource
Properties:
ImageId: !FindInMap [ RegionMap, !Ref "AWS::Region", 64]
InstanceType: m3.medium
InstanceInitiatedShutdownBehavior: terminate
UserData:
"Fn::Base64":
!Sub |
#!/bin/bash
# [Contents of bash script here...]
shutdown -h now