Userdata not populated properly in CfnInstance

[salovan]

• I'm submitting a ...

  • 🪲 bug report
  • 🚀 feature request
  • 📚 construct library gap
  • ☎️ security issue or vulnerability => Please see policy
  • ❓ support request => Please see note at the top of this template.

• What is the current behavior?
  I'm attempting to create EC2 instances with userdata to handle post-init configuration using the CfnInstance class. The userdata object is being created via the aws_ec2.UserData constructor.

from aws_cdk import (
    core,
    aws_ec2
)
class ConnectSmtpRouteStack(core.Stack):

    def __init__(self, scope: core.Construct, id: str, **kwargs) -> None:
        super().__init__(scope, id, **kwargs)

        shellCommands = aws_ec2.UserData.for_linux()
        shellCommands.add_commands("command1")
        shellCommands.add_commands("command2")

        ec2Instance1 = CfnInstance(self, 'ec2Instance1',
            image_id='ami-3ecc8f46',
            instance_type='t3.large',
            availability_zone='us-west-2b',
            user_data=shellCommands.render()
        )

The generated CloudFormation code fails with "Invalid BASE64 encoding of user data" error. The relevant YAML output looks like:

  ec2Instance1:
    Type: AWS::EC2::Instance
    Properties:
      AvailabilityZone: us-west-2b
      ImageId: ami-3ecc8f46
      InstanceType: t3.large
      UserData: >-
        #!/bin/bash

        command1

        command2

• What is the expected behavior (or behavior of feature suggested)?
  I would expect the generated UserData stanza to include the relevant Base64 encoding blocks. Something like:

      UserData:
        Fn::Base64: !Sub |
           #!/bin/bash
           command1
           command2

• What is the motivation / use case for changing the behavior or adding this feature?
  Immediately, I want to create an EC2 instance with additional data volumes which are partitioned, formatted, and mounted when the instance is initialized. There are other post-init workflows that I would like to build later

• Please tell us about your environment:

  • CDK CLI Version: 1.1.0 (build 1a11e96)
  • Module Version: aws-cdk=1.1.0,@aws-cdk/aws-cloudwatch=1.1.0,@aws-cdk/aws-ec2=1.1.0,@aws-cdk/aws-iam=1.1.0,@aws-cdk/aws-ssm=1.1.0,@aws-cdk/core=1.1.0,@aws-cdk/cx-api=1.1.0,@aws-cdk/region-info=1.1.0,jsii-runtime=Python/3.6.8
  • OS: Ubuntu 18.04
  • Language: Python

[alokito]

I have a related issue, I am trying to embed the IP address of another ec2 instance in the user data of a second ec2 instance with (apologies for the typescript vs python):

    const ec2Instance2 = new ec2.CfnInstance(this, 'ec2Instance2', {
          imageId: 'ami-3ecc8f46',
          instanceType:'t3.large',
          availabilityZone:'us-west-2b',
          userData:`export CDK_IP='${ec2Instance1.attrPrivateIp}'`
    });

This produces

  ec2Instance2:
    Type: AWS::EC2::Instance
    Properties:
      AvailabilityZone: us-west-2b
      ImageId: ami-3ecc8f46
      InstanceType: t3.large
      UserData:
        Fn::Join:
          - ""
          - - export CDK_IP='
            - Fn::GetAtt:
                - ec2Instance1
                - PrivateIp
            - "'"

This fails with a similar error due to lack of "Fn::Base64":

[alokito]

@salovan you may be able to work around this by using an AutoScalingGroup with one ec2 in it... unfortunately, I was unable to do this since in CDK the ASG always creates a new security group, and I cannot create security groups per corporate policy. I have filed a feature request for this: #3433

[AlexCheema]

I have a related issue, I am trying to embed the IP address of another ec2 instance in the user data of a second ec2 instance with (apologies for the typescript vs python):

    const ec2Instance2 = new ec2.CfnInstance(this, 'ec2Instance2', {
          imageId: 'ami-3ecc8f46',
          instanceType:'t3.large',
          availabilityZone:'us-west-2b',
          userData:`export CDK_IP='${ec2Instance1.attrPrivateIp}'`
    });

This produces

  ec2Instance2:
    Type: AWS::EC2::Instance
    Properties:
      AvailabilityZone: us-west-2b
      ImageId: ami-3ecc8f46
      InstanceType: t3.large
      UserData:
        Fn::Join:
          - ""
          - - export CDK_IP='
            - Fn::GetAtt:
                - ec2Instance1
                - PrivateIp
            - "'"

This fails with a similar error due to lack of "Fn::Base64":

You should be able to wrap your user data in use cdk.Fn.base64. Here's an example that works for me:

    const dbProxyInstance = new ec2.CfnInstance(this, "DBProxyInstance", {
      instanceType: "t3a.small",
      imageId: "ami-026c8acd92718196b",
      securityGroupIds: [dbProxySecurityGroup.securityGroupId],
      subnetId: vpc.publicSubnets[0].subnetId,
      userData: cdk.Fn.base64(
        `#!/bin/bash -xe 
apt-get -y update
apt-get -y install xorg xfce4 autocutsel chromium-browser
add-apt-repository -y ppa:x2go/stable
apt-get -y install -y x2goserver x2goserver-xsession
apt-get -y install gnome-icon-theme tango-icon-theme`
      )
    });

[alokito]

@AlexCheema that worked, thanks!

[rix0rrr]

CfnInstance will not automatically base64 for you. An AutoScalingGroup will, and the newly added Instance class will do so as well.

[Fzomerdijk]

Hi,
The CDK python example above misses the base64 encoding, the line should be:

user_data= core.Fn.base64(shellCommands.render())

Full code example:

from aws_cdk import (
    aws_ec2 as ec2,
    core
)

from .hello_construct import HelloConstruct

class MyStack(core.Stack):

    def __init__(self, scope: core.Construct, id: str, **kwargs) -> None:
        super().__init__(scope, id, **kwargs)

        shellCommands = ec2.UserData.for_linux()
        shellCommands.add_commands(
            "echo \"Install Java 1.8 jdk\"",
            "yum install java-1.8.0-openjdk -y"
        )

        StackStateInstance = ec2.CfnInstance(self, 'StackStateInstance',
            image_id='ami-1234567890',
            instance_type='t3.small',
            availability_zone='eu-central-1a',
            user_data= core.Fn.base64(shellCommands.render()) 
       )