Establishing SSH Connection to Private Instance over a Bastion Node in Go Using x/crypto/ssh

In this scenario, you aim to connect to a private instance (referred to as "service instance") from your local laptop over a bastion node deployed within AWS VPC containing public and private subnets. You intend to execute commands on the service instance and transfer files from your local laptop.

To achieve this using Go's "x/crypto/ssh" library:

1. Establish Connection to Bastion Host:

   • Create an ssh.Client representing the connection to the bastion host.

2. Establish Connection to Service Instance from Bastion:

   • Utilize the Dial method of the bastion client to establish a virtual net.Conn between you and the service instance.

3. Create New SSH Client for Service Instance:

   • Convert the net.Conn to an ssh.Conn using ssh.NewClientConn.
   • Create a new ssh.Client (sClient) for communication with the service instance.

4. Execute Commands and Transfer Files:

   • Utilize the sClient to execute commands on the service instance.
   • Implement file transfer mechanisms (e.g., SFTP) to upload files from your local laptop to the service instance.

Below is a code snippet demonstrating these steps:

// connect to the bastion host
bClient, err := ssh.Dial("tcp", bastionAddr, config)
if err != nil {
    log.Fatal(err)
}

// Dial a connection to the service host, from the bastion
conn, err := bClient.Dial("tcp", serviceAddr)
if err != nil {
    log.Fatal(err)
}

ncc, chans, reqs, err := ssh.NewClientConn(conn, serviceAddr, config)
if err != nil {
    log.Fatal(err)
}

sClient := ssh.NewClient(ncc, chans, reqs)

With sClient, you can execute commands and transfer files to and from the service instance.