How To Manage SSH Connections for Multiple Machines

If you want to work with many remote Linux machines, managing and remembering IP addresses, user names and keys would be a little hard.

If you are using ssh clients like putty, you can store the session, but if you are the devops engineer who uses a terminal to do ssh, there should be a managed way to connect remote machines.

In this guide, you will learn to make use of ssh config file which stores all you ssh information that’s needed for the ssh connection.

SSH Connections for Multiple Machines

Every Linux and Unix-based machine has a .ssh folder where you keep your ssh keys. In this folder, you can have a file named “config” and you can put all the remote machine details in this file.

Now create a config file in your .ssh folder using the following command.

touch ~/.ssh/config

A sample configuration is shown below.

Host nodejs
  HostName nodejs.myserver.com
  Port 22
  User yahooda

Host nodejs
  HostName database.myserver.com
  Port 22
  User yahooda
  IdentityFile ~/.ssh/mykey.pem

We have declared “nodejs” (Host) as an identifier for our remote host in the above snippet. All the other parameters are self-explanatory. For example, if your server does not have a domain name, you can give the IP address instead of the domain name.

Connecting Configured Machines

Now you have entered all the configurations that are needed to connect to remote machines. Now to connect, all you have to do is use ssh command with the identifier you used in the config file. An example is shown below.

ssh nodejs

The above command will look for nodejs identifier in the config file and will pick all the parameters from the config file for the remote ssh connection.

Defining Common SSH Parameters

You need to manage ten servers, and all the servers have the same username and ssh key. In this case, you can define the common parameters under one block with a regular expression. An example for defining the common parameters is shown below.

Host dev

Host web.node1

Host web.node2

Host *
  Port 4556
  User jordan
  IdentityFile ~/.ssh/jordan_privatekey

Host web*
  Port 4668
  User james
  IdentityFile ~/.ssh/james_privatekey

In the above example Host * means, the parameters described in that block apply to all the servers. Host web* .The parameters described in that block apply to all the host definitions that start with the web keywords in the identifiers.