Automating SSH configuration

automate configuring SSH settings on local machines for every new remote server we create on AWS by using provisioner "local-exec" in Terraform.

Use case

Using the "local-exec" provisioner in Terraform to make changes to the .ssh/config file is a common use case for configuring SSH settings on local machines. For example, if you have multiple servers that you frequently SSH into, you can use Terraform to dynamically update your .ssh/config file with the necessary configuration for each server. This can help streamline your SSH workflow and make it easier to manage your SSH connections.

Installation

1. Initialise terraform directory

terraform init

2. run terraform plan

terraform plan

3. Provision AWS infrastructure

terraform apply -auto-approve

Description of architecture on AWS

After running the above command you will have :

• vpc (10.0.0.0/16)
• public subnet(10.0.1.0/24)
• internet gateway and route table
• security group allowing ssh and http to '0.0.0.0/0'
• ec2 instance
• latest ami_id is pulled using datasource "aws_ami"

provisioner "local-exec"

local-exec is used to run commands on your local machiner after terraform apply command is used.

command =templaterfile() will look for the file specified and run commands in that file.

In this code, local-exec will run a mac-ssh-config.tpl file containing necessary code to create a local ssh development environment.

provisioner "local-exec" {
    command     = templatefile("${var.host_os}-ssh-config.tpl", 
   { hostname = self.public_ip, user = "ubuntu", identityfile = "~/.ssh/aws_key_pair" })
    interpreter = var.host_interpreter
  }

variables are defined in terraform.tfvars

host_interpreter=["bash","-c"] # replace it with ["powershell","-command"] for windows user

host_os="mac-linux" # replace it with "windows" for windows user

Setting up template file for ~/.ssh/config

• create a mac-ssh-config.tpl file

cat << EOF >> ~/.ssh/config

Host ${hostname}
    HostName ${hostname}
    User ${user}
    IdentityFile ${identityfile}
EOF

for windows use windows-ssh-config.tpl file

add-content -path c:/users/tusharthapliyal/.ssh/config -value @'

Host ${hostname}
    HostName ${hostname}
    User ${user}
    IdentityFile ${identityfile}

'@

variables for this file will are defined within provisioner block.

Note

If you ever decide to go with some other AWS AMI, other than Ubuntu, You will need to change the username in configuration tpl file. default username for ubuntu = "ubuntu" default username for Amazon Linux = "ec2-user".

VS code extensions

Download remote ssh extension in VScode to connect to your remote instance.