If you have means to directly access to the various machines you intend to connect to through the bastion host (such as through a VPN tunnel or temporarily connecting to the same physical network) then you should be able to ssh into them without an account password as well. ![]() With that the basics of public-key authentication are handled: You can ssh into the bastion host without a password. For linux/unix OSs, it’s recommended to add ssh-agent to the shell’s login, and then call ssh-add after login and before using ssh.(The keychain is usually unlocked as long as the user is logged in and the screen isn’t locked.) The automatically started ssh-agent will then be able to access those keys in the keychain as long as the keychain is unlocked. When you generate a key, call ssh-add with the OS X-only -K option to add it’s passphrase to the user’s keychain. NOTE: In OS X, the ssh-agent is automatically started at login, and has been extended to grab an SSH key’s passphrase from the user’s keychain.ssh-agent(1) is running and all of the key pairs to be used have been ssh-add(1)ed, thus allowing each key to be used without (further) entering a password.If it fails, check for incorrect permissions to the file and it’s containing directories, and verify that authorized-keys is not disabled in the sshd config of the destination machine. That each machine (including the bastion host) already has the relevant public-key copied to ~/.ssh/authorized_keys, thereby granting access to the holder of the corresponding private key - hopefully, that’s just you! This should be tested and proven to allow login to that machine from the client machine without an account password.You could of course use a single key pair for all machines, or one key pair for the bastion host and another for all the other machines, or any combination of the above. From here on we’ll assume one key pair per machine you’re connection to, including one for the bastion host itself.One or more key pairs in ~/.ssh/ that are secured by password(s).However you get there, we’ll need to end up with: There are many references on the internet about how to generate key pairs that can be used for ssh, such as for GitHub, Amazon AWS, Google Compute Engine, and there’s always the ssh-keygen(1) man page. In order to efficiently and (arguably) securely connect to multiple machines from one machine, we’ll be using Public Key Authentication in SSH. Configuring Ansible to use an SSH bastion host.Using SSH bastion hosts with AWS, and dynamically locating them with EC2 tags.SSH connection multiplexing, port forwarding, and use as a SOCKS proxy.Dynamically located SSH bastion hosts with AWS.In follow-up posts, I’ll cover these related topics: Making the connection transparently using the bastion host based on destination.Making the connection through the bastion host to the destination machine in one step.The mechanics of using SSH to connect to the bastion host, and from there SSH to another machine without having to store authentication information on the bastion host.The purpose of using a bastion host for access is clearly a matter of increased security. We won’t be going deeply into the security implications in this article. ![]() We will be demonstrating how to make that connection transparent and automatic, not only for manual SSH connections but also for programmatic SSH connections such as with GIT or Ansible. Here we will be using a bastion host to serve as a SSH server that we can “hop” through into another machine (real or VM), allowing users to automate remote task execution over SSH. ![]() However, adding bastion hosts creates complexity in remote execution of scripts or deployment tasks. Having a bastion host is a good security practice commonly deployed to strengthen yet simplify security controls of an environment. It is hardened in this manner primarily due to its location and purpose, which is either on the outside of the firewall or in the DMZ and usually involves access from untrusted networks or computers. The computer generally hosts a single application, for example a proxy server, and all other services are removed or limited to reduce the threat to the computer. A Bastion host is a special purpose computer on a network specifically designed and configured to withstand attacks.
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