SSH

Tips

Static config

Util ssh able to using predefined configurations. The most popular place to check ~/.ssh/config, /etc/ssh/ssh_config

Example:

Host baloo
   Hostname <hostname>
   Port <port>
   User <username>
   LocalForward 3000 localhost:3000
   LocalForward 8080 localhost:8080
   LocalForward 4646 localhost:4646
   LocalForward 9090 localhost:9090
   ForwardAgent yes

Hostname baloo like an alias will using to connect via SSH.

$ ssh baloo

Generate key

$ ssh-keygen -t ed25519

Copy a generated key into a target host

$ ssh-copyid -l <username> <target_host>

Connect to host through LoadBalancer

• LoadBalancer have to know about HostSNI which passing in request;
• Resolve will be running on LoadBalancer side;
• Source host might carreless about target_host FQDN.

Scheme:

flowchart LR
    A[User] -->|TCP/443| C(LoadBalancer)
    C -->|TCP/22| D[SSH]

$ ssh -o "ProxyCommand=openssl s_client -quiet -servername %h -connect <loadbalancer_host>:<loadbalancer_port>" <target_host> 

Make a tunnel between source host and target

Imagine a situation on target_host exists to running a process on loopback interface, which not availabled outside.

$ ss -tanpl | grep 127.0.0.1

LISTEN  0        1024           127.0.0.1:8080          0.0.0.0:*

We can make to able reacheble from source_host thought ssh util.

$ ssh -L 127.0.0.1:8080:8080 <target_host>

How to transfer files through SSH connection

Basically rsync or scp can transfer data through SSH connection. However in case when just pure SSH you also can doing that.

Transfer files from localhost to the remote host

$ tar -czf - <SRC_FOLDER> | ssh <REMOTE_HOST> tar -xzf - -C <DEST_FOLDER>

Transfer data from the remote host on localhost

$ ssh <REMOTE_HOST> tar -czf - <SRC_FOLDER> | tar -xzf - -C <DEST_FOLDER>

ssh-agent

The util ssh-agent provide to make easy process to forward auth through other host/hosts.

$ eval (ssh-add)              # Sometime requires to use `eval` to init ssh-agent
$ ssh-add                     # Add key to ssh agent
$ ssh-add -L                  # Check already added keys
$ ssh <target_host> -A        # Enable Agent-Forwarding(On target host also have to enabled)
<target_host> $ ssh-add -L    # Check already added keys on target host after login on target host
$ env | grep SSH_AUTH_SOCK    # Place where storing ssh-agent sock