Can't SSH into AWS CloudFormation Stack Instance

The problem is that the CloudFormation template creates a RouteTable with the default route 0.0.0.0/0 correctly pointing to the IGW, however you don't associate the RouteTable with your subnets.

What you need to do is add these two Route Table Associations to the template:

        "Subnet1RT":{
            "Type" : "AWS::EC2::SubnetRouteTableAssociation",
                "Properties" : {
                    "RouteTableId" : { "Ref": "RouteTable" },
                    "SubnetId" : { "Ref": "Subnet1" }
                }
        },
        "Subnet2RT":{
            "Type" : "AWS::EC2::SubnetRouteTableAssociation",
                "Properties" : {
                    "RouteTableId" : { "Ref": "RouteTable" },
                    "SubnetId" : { "Ref": "Subnet2" }
                }
        },

Then Update the stack ...

And re-check the Route Table

Now you should be able to SSH to the instances:

~ $ ssh 54.209.123.119
Last login: Thu Nov  1 18:54:54 2018 from ...

       __|  __|_  )
       _|  (     /   Amazon Linux AMI
      ___|\___|___|

https://aws.amazon.com/amazon-linux-ami/2018.03-release-notes/
[ec2-user@ip-10-0-2-229 ~]$ 

Hope that helps :)