Getting cloud formation error Value of property InstanceId must be of type String while attaching eip with ec2

Question

AWSTemplateFormatVersion: '2010-09-09'
Resources:
  DevEC2Instance:
    Type: AWS::EC2::Instance
    Properties:
      InstanceType: t2.micro
      ImageId: ami-0e322da50e0e90e21
      KeyName: "cnf-key-1"
      SecurityGroups: 
         - default
         - Ref:  SSHSecurityGroup

  SSHSecurityGroup:
     Type: AWS::EC2::SecurityGroup
     Properties:
        GroupDescription: my new SSH SG
        SecurityGroupIngress:
          - IpProtocol: tcp
            FromPort: '22'
            ToPort: '22'
            CidrIp: 0.0.0.0/0
          - IpProtocol: tcp
            FromPort: '8080'
            ToPort: '8080'
            CidrIp: 0.0.0.0/0

  MyElasticIP:
    Type: AWS::EC2::EIP
    Properties:
      InstanceId: 
         - Ref: 'DevEC2Instance'

Answer 1

Due to - you are creating a list. Instead it should be:

  MyElasticIP:
    Type: AWS::EC2::EIP
    Properties:
      InstanceId: !Ref DevEC2Instance