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AWS CloudFormation - EC2 UserData

AWS CloudFormation EC2 UserData.

EC2 UserData is a way to define multiple actions within ec2 instnace once the system gets first time started, if you are from a Linux background you might be familiar with rc.local file where we used to write all the commands or script action that needs to be executed whenever a system gets booted up.
It's somehow similar to that but not the same at all.

Something more about EC2 UserData
  • We can use UserData in CFN template for EC2. 
  • We need to use an intrinsic function Fn::Base64 with UserData in CFN template, this function return the Base64 representation of string, it passes encoded data to EC2 instance.
  • Multiple Line values can be used under Base64 followed by YAML Pipe ( | )
  • UserData scripts/commands runs during the boot cycle when we first launch the instance.
  • To Update and reflect the changes under the value of UserData, reboot is required.
  • Can be used the same way normal parameters are used via !Ref as an argument.
Usage Example.

Below CFN template along with UserData section is used to install to perform three steps.
  • Update YUM
  • Download Logstash using Wget
  • Install downloaded RPM
AWSTemplateFormatVersion: 2010-09-09
Description: A Cloudformation Script to demonstrate EC2 UserData

Type: "AWS::EC2::Instance"
ImageId: ami-01460aa81365561fe
InstanceType: t2.micro
KeyName: kunal_eks_test
SubnetId: subnet-0cdcc621
IamInstanceProfile: "IamInstanceProfile"
- launch-wizard-1
Fn::Base64: |
sudo yum update -y
sudo wget
sudo rpm -Uvh logstash/logstash-7.1.0.rpm

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