Why I could not ssh to my AWS ec2 instance that I created using AWS CloudFormation?

Question

I am creating an EC2 instance using CloudFormation which has VPC, subnet and Security Group mentioned. However, when instance spins up I am not able to ssh to the instance and get the following message:

ssh -i aws_jenkins.pem ec2-user@34.217.129.89

The authenticity of host '34.217.129.89 (34.217.129.89)' can't be established. ECDSA key fingerprint is SHA256:rs3bjVKolzdmktzfiSd0Oo5RU6dLdT/PGHpycStgFK8. ECDSA key fingerprint is MD5:7f:cc:61:c4:f3:1a:b7:45:9a:f0:da:e8:0c:a4:d9:bc.

Are you sure you want to continue connecting (yes/no)? yes

Warning: Permanently added '34.217.129.89' (ECDSA) to the list of known hosts.

Permission denied (publickey,gssapi-keyex,gssapi-with-mic).

However, if I create another EC2 from AWS Console

Using the same ImageID, VPC, Subnet, SecurityGroup and Key. I can SSH to it.

But why the instance that is created via CloudFormation is not SSH able

I am not able to resolve this, any insight/solution is very much appreciated.

AWSTemplateFormatVersion: 2010-09-09

Parameters:

  EnvironmentName:
    Description: An environment name that will be prefixed to resource names
    Type: String

  VpcCIDR: 
    Description: Please enter the IP range (CIDR notation) for this VPC
    Type: String
    Default: 10.192.0.0/16

  PublicSubnet1CIDR:
    Description: Please enter the IP range (CIDR notation) for the public subnet in the first Availability Zone
    Type: String
    Default: 10.192.10.0/24

  PublicSubnet2CIDR:
    Description: Please enter the IP range (CIDR notation) for the public subnet in the second Availability Zone
    Type: String
    Default: 10.192.11.0/24

  InstanceType:
    Description: WebServer EC2 instance type
    Type: String
    Default: t2.micro
    AllowedValues: [ t1.micro, t2.nano, t2.micro, t2.small, t2.medium]
    ConstraintDescription : must be a valid EC2 instance type.

  KeyName:
    Description: The EC2 Key Pair to allow SSH access to the instances
    Type: AWS::EC2::KeyPair::KeyName
    Default: jenkins-test
    ConstraintDescription: must be the name of an existing EC2 KeyPair.

  SSHLocation: 
    Description: The IP address range that can be used to SSH to the EC2 instances
    Type: String
    MinLength: 9
    MaxLength: 18
    Default: 0.0.0.0/0
    AllowedPattern: "(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})/(\\d{1,2})"
    ConstraintDescription: must be a valid IP CIDR range of the form x.x.x.x/x.

Resources:

  VPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: !Ref VpcCIDR
      EnableDnsSupport: true
      EnableDnsHostnames: true
      Tags: 
      - Key: Name
        Value: !Ref EnvironmentName

  InternetGateway:
    Type: AWS::EC2::InternetGateway
    DependsOn: VPC
    Properties:
      Tags:
      - Key: Name
        Value: !Ref EnvironmentName

  InternetGatewayAttachment:
    Type: AWS::EC2::VPCGatewayAttachment
    Properties:
      InternetGatewayId: !Ref InternetGateway
      VpcId: !Ref VPC

  PublicSubnet1: 
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref VPC
      AvailabilityZone: !Select [ 0, !GetAZs ]
      CidrBlock: !Ref PublicSubnet1CIDR
      MapPublicIpOnLaunch: true
      Tags: 
      - Key: Name 
        Value: !Sub ${EnvironmentName}-Public-Subnet-(AZ1)

  PublicSubnet2:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref VPC
      AvailabilityZone: !Select [ 1, !GetAZs ]
      CidrBlock: !Ref PublicSubnet2CIDR
      MapPublicIpOnLaunch: true
      Tags:
      - Key: Name
        Value: !Sub ${EnvironmentName}-Public-Subnet-(AZ2)     

  PublicRouteTable:
    Type: AWS::EC2::RouteTable
    Properties: 
      VpcId: !Ref VPC
      Tags: 
      - Key: Name 
        Value: !Sub ${EnvironmentName} Public Routes

  DefaultPublicRoute: 
    Type: AWS::EC2::Route
    DependsOn: InternetGatewayAttachment
    Properties: 
      RouteTableId: !Ref PublicRouteTable
      DestinationCidrBlock: 0.0.0.0/0
      GatewayId: !Ref InternetGateway

  PublicSubnet1RouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      RouteTableId: !Ref PublicRouteTable
      SubnetId: !Ref PublicSubnet1

  PublicSubnet2RouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    Properties:
      RouteTableId: !Ref PublicRouteTable
      SubnetId: !Ref PublicSubnet2


  InstanceSecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Enable SSH access and HTTP to instance
      SecurityGroupIngress:
      - IpProtocol: tcp
        FromPort: 22
        ToPort: 22
        CidrIp: !Ref SSHLocation

      - IpProtocol: tcp
        FromPort: 80
        ToPort: 80
        CidrIp: !Ref SSHLocation
      VpcId: !Ref VPC
      Tags:
      - Key: Name
        Value: TestSecurity_group

  MyInstance:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: ami-061392db613a6357b
      InstanceType: !Ref InstanceType
      SubnetId: !Ref PublicSubnet1
      KeyName: !Ref KeyName
      SecurityGroupIds:
      - !Ref InstanceSecurityGroup
      Tags:
      - Key: Name
        Value: TestServer

Answer 1

In your parameters you have:

KeyName:
    Description: The EC2 Key Pair to allow SSH access to the instances
    Type: AWS::EC2::KeyPair::KeyName
    Default: jenkins-test
    ConstraintDescription: must be the name of an existing EC2 KeyPair.

1. Are you letting it build using this default parameter?
2. Are you sure you are using the correct matching key?