Cloudformation template completes deployment before UserData is finished - amazon-web-services

Question

In the CloudFormation template I am deploying, I am running a long running operation in the UserData block.
It looks as follows:
"UserData": {
"Fn::Base64" : {
"Fn::Join" : [
"",
[
"/usr/local/bin/mylongrunningscript.sh"
]
]
}
}
The contents of the script are:
echo "UserData starting!" > /var/log/mycustomlog.log
sleep 300
echo "UserData finished!" >> /var/log/mycustomlog.log
The issue I am seeing is that I believe the CloudFormation template is completing it's deployment before the UserData script finishes running. I believe this is the case because if I am quick enough and ssh into the instance, I will see something as follows:
$ cat /var/log/mycustomlog.log
UserData starting
which suggests that the UserData didn't finish running
How can I make sure that the UserData code execution is completed before the stack is in the "CreateComplete" status?

Answer 1

To ensure the CloudFormation template waits for the completion of the UserData script, you must do two things:
Add a CreationPolicy to the resource you are targeting (virtual machine in my case).
Add logic in the script to signal its completion. This custom logic uses the cfn-signal utility, which you might have to install in your instance.
Here's how the template looks now:
"UserData": {
"Fn::Base64" : {
"Fn::Join" : [
"",
[
"/usr/local/bin/mylongrunningscript.sh"
]
]
}
},
"CreationPolicy": {
"ResourceSignal" : {
"Count": "1",
"Timeout": "PT10M"
}
}
The cfn-signal utility is used to signal the termination of the script:
"/home/ubuntu/aws-cfn-bootstrap-*/bin/cfn-signal -e $? ",
" --stack ", { "Ref": "AWS::StackName" },
" --resource MyInstance" ,
" --region ", { "Ref" : "AWS::Region" }, "\n"
See here for a Windows example.