When you deploy your application in cloud you don’t need and don’t want your hosts exposed via SSH to the world. Malware scans whole network for easy SSH access and when find something will try some brute force attacks, overloading such machines. It’s easier to have one exposed, but secured host, that doesn’t host anything and is used as proxy/gateway to access our infrastructure- it’s called bastion host.
Ansible is quite easy to integrate with bastion host configuration. We will need custom
ssh_config file. So let’s start with
Host bastion Hostname ip.xxx.xxx.xxx.xxx.or.host.name User ubuntu IdentityFile ~/.ssh/id_rsa PasswordAuthentication no ForwardAgent yes ServerAliveInterval 60 TCPKeepAlive yes ControlMaster auto ControlPath ~/.ssh/ansible-%r@%h:%p ControlPersist 15m ProxyCommand none LogLevel QUIET Host * User ubuntu IdentityFile ~/.ssh/id_rsa ServerAliveInterval 60 TCPKeepAlive yes ProxyCommand ssh -q -A ubuntu@bastion nc %h %p LogLevel QUIET StrictHostKeyChecking no
Now I will describe what most important options mean. For bastion:
User– I’m using Ubuntu kickstarted on cloud as bastion host with it’s default user. Never use root here – you don’t need that
ForwardAgent yes– we want to forward our ssh keys through bastion to destination hosts,
ServerAliveInterval 60– this is like keepalive connection, ssh will send small ping/pong packets every 60 seconds so your connection won’t hung/terminate after long time,
ControlMaster auto– we will open one connection to bastion host and multiplex other ssh connections through it, connection will be opened for
ControlPath– this have to be configured same way like in
ProxyCommand none– we’re setting
ProxyCommandfor all hosts but we need it disabled for bastion,
Default hosts configuration:
ProxyCommand ssh -q -A ubuntu@bastion nc %h %p– this is what makes all magic, it will pipe your ssh connection via bastion to destination host,
StrictHostKeyChecking no– this options shouldn’t be there for production but it’s useful at beginning when you create and destroy machines few times before you test everything. Normally this will cause notifications about ssh key changes, but you’re aware of that – you just recreated those machines.
I’ve found examples without netcat but was unable to get them working – this one worked for me really well.
To test if connections work fine use this configuration like:
ssh -F ssh_config bastion ssh -F ssh_config other.host.behind.bastion
[defaults] forks=20 [ssh_connection] ssh_args = -F ./ssh_config -o ControlMaster=auto -o ControlPersist=5m -o LogLevel=QUIET control_path = ~/.ssh/ansible-%%r@%%h:%%p pipelining=True
Most important section here is in
ssh_args where we’re pointing to
ssh_config file in current dir with
-F option. I also have to reenter configuration for multiplexing here – it wasn’t working with ssh only configuration.
control_path option have to use same paths like
% signs are escaped with
You should be able to run
ansible-playbook commands normally now – all traffic will be forwarded through bastion.
It’s good time now to install
fail2ban on bastion and maybe reconfigure it to run
ssh on crazy high port 🙂