Optimize Your SSH Connections With SSH Config File

If most of your work is done remotely though ssh, and you have to access several environments, there will come a time where you need to organize our connection settings. Which user you need to access server X or which port is configured or the case you work in consulting and have several ssh_keys.

There are some tools that migth help on this, but i’m old school and still stick with plain ssh command.

ssh config file helps quite a lot, here are some tips unknown to some:

Alias

Let’s say you want to take advantage of tab auto-completion when using your connections for a enviroment like

├── ClientA
│   ├── server1
│   └── server2
├── ClientB
│   └── server1
├── DEV
│   ├── BackOffice
│   │   ├── server1
│   │   └── server2
│   └── FrontOffice
│       ├── server1
│       ├── server2
│       └── server3
├── LIVE
│   ├── Cluster
│   │   ├── node01
│   │   ├── node02
│   │   └── node03
│   └── Servers
│       ├── server01
│       └── server02
└── QA
    └── server1

this would be quicker to do something like ssh DEV TAB Back TAB server1

that’s actually possible with ssh_config alias.

Add the following to ~/.ssh/config to see this in action

Host ClientA.server1
     Hostname localhost
Host ClientA.server2
     Hostname localhost
Host ClientB.server1
     Hostname localhost
Host ClientA.server1
     Hostname localhost
Host DEV.BackOffice.server1
     Hostname localhost
Host DEV.BackOffice.server2
     Hostname localhost
Host DEV.FrontOffice.server1
     Hostname localhost
Host DEV.FrontOffice.server2
     Hostname localhost
Host DEV.FrontOffice.server3
     Hostname localhost
Host LIVE.Cluster.node01
     Hostname localhost
Host LIVE.Cluster.node02
     Hostname localhost
Host LIVE.Cluster.node03
     Hostname localhost
Host LIVE.Servers.server01
     Hostname localhost
Host LIVE.Servers.server02
     Hostname localhost
Host QA.server01
     Hostname localhost

Now try out the power of Tab-autocompletion. this is just an example of a type of structure you could use.

You could also add alias like

Host LIVE.Servers.server02 server01.mydomain.com
     Hostname localhost

So that both ssh attempts to LIVE.Servers.server02 and server01.mydomain.com would use the same configuration.

Access customizations

No let’s say for accessing LIVE.Servers.server01 you require account admin and ssh listens on port 2228 . one could setup the following

Host LIVE.Servers.server01
     Hostname localhost
     Port 2228
     User admin

With this configuration one could simple execute ssh LIVE.Servers.server01 and it will use the configured user and port in the connection.

Or if you have a specific ssh_key for it in QA

Host QA.server01
     Hostname localhost
     Port 2227
     User qa_user01
     IdentityFile ~/.ssh/id_rsa_qa

Tunnels

one could also setup tunnels directly in ssh_config like

Host tunnel
    HostName database.example.com
    IdentityFile ~/.ssh/id_rsa_dev
    LocalForward 9906 127.0.0.1:3306
    User dba

You can simple execute ssh -f -N tunnel

Or if you have access to server3 only from server1

Host DEV.FrontOffice.server3
     Hostname 10.0.0.1
     Port 22
     User admin
     IdentityFile ~/.ssh/id_rsa_dev
     ProxyCommand ssh -q -W %h:%p DEV.FrontOffice.server1

One configuration i normally use in development with containers or virtual machines wich are deprovision with regularity is the following:

Host 192.168.77.* mesos-*
   StrictHostKeyChecking no
   User rramos
   IdentityFile ~/.ssh/id_rsa
   UserKnownHostsFile=/dev/null
   LogLevel QUIET

This means any ssh connection to local network 192.168.77.* or hosts with name mesos-* wont get registered in KnownHosts.

You could also use this to change your settings for TCPKeepAlive or any other specific connections settings you may need the man page as the full list of options.

Cheers,
RR

References