Route SSH connections through a bastion host

ssh.config

Host bastion_ip
    User                   ec2-user
    HostName               ##.##.##.##
    ProxyCommand           none
    IdentityFile           ~/.ssh/bastion_key.pem
    BatchMode              yes
    PasswordAuthentication no

Host *
    ServerAliveInterval    60 
    TCPKeepAlive           yes 
    ProxyCommand           ssh -q -A ec2-user@bastion_host -i ~/.ssh/bastion-key.pem nc %h %p 
    ControlMaster          auto 
    ControlPath            ~/.ssh/mux-%r@%h:%p 
    ControlPersist         8h 
    User                   ubuntu
    StrictHostKeyChecking  no
    IdentityFile           ~/.ssh/applicatio-server-key.pem