This is a text-only version of the following page on https://raymii.org:
---
Title       : 	Clear Uncluttered SSH client config with Ansible
Author      : 	Remy van Elst
Date        : 	21-12-2014
URL         : 	https://raymii.org/s/blog/Clear_Uncluttered_SSH_client_config_with_Ansible.html
Format      : 	Markdown/HTML
---



Openssh allows you to configure parameters like username, port, proxycommand,
key and more in the ~/.ssh/config file. If you have many servers this file can
become cluttered and maintaining it can become a not so nice task. This simple
guide shows you how you can use a conf.d directory with seperate smaller files
which gets converted to the big config file by Ansible.

I need to manage a lot of linux servers. With a lot I mean almost a thousand
servers. Some of those servers require VPN, some of those servers are clusters
and some of those servers require a seperate key, username, port or
configuration. I don't like the big `~/.ssh/config` file which, in my case, is
extremely large.

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I much rather prefer the `conf.d` type structure with a lot of small files.
OpenSSH does not support this, however, Ansible has the [assemble][2] module
which, given a set of files or a folder, assembles a configuration file based on
all the given files.

Using this Ansible module together with a `local connection` we can assemble the
configuration file on our own machine.

Create the `~/.ssh/conf.d` folder:

    
    
    mkdir ~/.ssh/conf.d/ 
    

Split your configuration up in smaller parts, like below:

    
    
    $ ls -larth ~/.ssh/conf.d
    total 36M
    -rw-r--r-- 1 user user  396 Sep 27 14:07 defaults
    -rw-r--r-- 1 user user  216 Sep 27 14:07 client1
    -rw-r--r-- 1 user user 4812 Dec 10 04:03 client2
    -rw-r--r-- 1 user user  216 oct  5 08:37 client3
    

Copy the following Ansible playbook locally:

    
    
    - name: SSH config assembler
      hosts: 127.0.0.1
      connection: local
    
      tasks:
    
      - assemble: src=/home/user/.ssh/conf.d dest=/home/user/.ssh/config
    

Don't forget to change the username to yours.

And run it:

    
    
    ansible local_ssh.yml
    

You now have the big `~/.ssh/config` file generated out of the small files.

My `defaults` file contains the following:

    
    
    ###################################
    # Start Defaults                  #
    ###################################
    
    ForwardX11 yes
    GSSAPIAuthentication no
    HashKnownHosts yes
    
    Host *
      ConnectTimeout 90
      ServerAliveInterval 10
      ControlMaster auto
      ControlPersist yes
      ControlPath ~/.ssh/socket-%r@%h:%p
      RemoteForward 8022 localhost:22
    

The `clientX` files contain specific client configuration:

    
    
    Host web-jumphost
      Hostname 10.39.179.2
      User remy
      IdentityFile ~/.ssh/id_rsa_clientX
      Port 22
    
    Host web22 web22.example.org
      Hostname 10.39.100.5
      ProxyCommand ssh -W %h:%p -i ~/.ssh/id_rsa web-jumphost
      User remy
      IdentityFile ~/.ssh/id_rsa_clientX
      Port 22
    

To read more about the ssh client config file, see the manual page:
<http://linux.die.net/man/5/ssh_config>

   [1]: https://www.digitalocean.com/?refcode=7435ae6b8212
   [2]: http://docs.ansible.com/assemble_module.html

---

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