Teleport
Using Teleport with OpenSSH in agentless mode
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Using Teleport with OpenSSH
Length: 16:04
In this guide, we will show you how to configure Teleport in agentless mode and
have the OpenSSH server sshd
join a Teleport cluster. Existing fleets of
OpenSSH servers can be configured to accept SSH certificates dynamically issued
by a Teleport CA.
Using Teleport and OpenSSH has the advantage of getting you up
and running, but in the long run, we would recommend replacing sshd
with teleport
.
teleport
SSH servers have support for multiple features that are incompatible with OpenSSH:
- RBAC and resource filtering based on dynamically updated labels
- Session recording without SSH connection termination
- Session sharing
- Advanced session recording
Teleport supports OpenSSH by proxying SSH connections through the Proxy Service. When a Teleport user requests to connect to an OpenSSH node, the Proxy Service checks the user's Teleport roles.
If the RBAC checks succeed, the Proxy Service authenticates to the OpenSSH node with a dynamically generated certificate signed by a Teleport CA. This allows the Proxy Service to record and audit connections to OpenSSH nodes.
The Proxy Service prevents Teleport users from bypassing auditing by requiring a certificate signed by a Teleport CA that only the Auth Service possesses.
In this setup, the Teleport SSH Service performs RBAC checks as well as audits and records sessions on its host, which eliminates the need for connection termination when recording SSH sessions.
Registering an OpenSSH node with Teleport involves copying the teleport
binary
onto your sshd
host. The teleport
binary will handle registering the node
with your cluster, generating certificates, modifying your OpenSSH sshd
config,
and more. If copying the teleport
binary onto your sshd
and running it isn't
an option, you can register your node manually instead.
Prerequisites
-
OpenSSH version 6.9 or above on your local machine. View your OpenSSH version with the command:
ssh -V
-
A running Teleport cluster version 16.4.10 or above. If you want to get started with Teleport, sign up for a free trial or set up a demo environment.
-
The
tctl
admin tool andtsh
client tool.Visit Installation for instructions on downloading
tctl
andtsh
.
- A Linux host with the OpenSSH server
sshd
version 7.4 or above installed, but not Teleport. The SSH port on this host must be open to traffic from the Teleport Proxy Service host. - To check that you can connect to your Teleport cluster, sign in with
tsh login
, then verify that you can runtctl
commands using your current credentials. For example:If you can connect to the cluster and run thetsh login --proxy=teleport.example.com --user=[email protected]tctl statusCluster teleport.example.com
Version 16.4.10
CA pin sha256:abdc1245efgh5678abdc1245efgh5678abdc1245efgh5678abdc1245efgh5678
tctl status
command, you can use your current credentials to run subsequenttctl
commands from your workstation. If you host your own Teleport cluster, you can also runtctl
commands on the computer that hosts the Teleport Auth Service for full permissions.
Upgrading to v14 from legacy OpenSSH nodes
If you have previously configured OpenSSH nodes to trust a Teleport CA without registering them and you upgrade your Teleport cluster to Teleport 14, you won't be able to connect to them anymore by default. This is because open dialing to OpenSSH servers not registered with the cluster is no longer allowed in Teleport 14. To ensure that you will retain access to your OpenSSH nodes you will need to follow this guide to register every OpenSSH node with Teleport that you previously configured. This must be done before your Teleport cluster is upgraded to Teleport 14.
If you are having issues registering OpenSSH nodes or need to upgrade your
Teleport cluster to Teleport 14 before registering all of your OpenSSH nodes, you can
pass the TELEPORT_UNSTABLE_UNLISTED_AGENT_DIALING
environment variable to your
Proxy Service and set it to yes
. This will allow connections to unregistered
OpenSSH nodes but will be removed in Teleport v15.
Step 1/3. Configure sshd
Teleport only allows access to resources in your infrastructure via Teleport processes that that have joined the cluster.
To register the OpenSSH node, you must have a valid auth token to connect to the cluster. You can generate the token by running the following command against your Teleport Auth Service:
tctl tokens add --type=node --format=textabcd123-insecure-do-not-use-this
Copy the teleport
binary to your sshd
host. Configure sshd
and create a node
resource on your cluster with the following command:
sudo teleport join openssh \ --address server1.example.com:22 \ --proxy-server teleport.example.com:443 \ --join-method token \ --token abcd123-insecure-do-not-use-this \ --labels env=dev
Change the command-line options to assign the following values:
- server1.example.com:22 Set to the address and port of the node that will join your Teleport cluster.
- teleport.example.com:443 Set to the address and port of your Teleport Proxy Service.
- abcd123-insecure-do-not-use-this Set to the join token value.
Check that your new node is listed with tsh ls
or in the Web UI. You can edit the
hostname and labels with tctl edit nodes/<hostname>
. If the hostname isn't unique, get the UUID
from tctl nodes ls -v
and edit with tctl edit nodes/<uuid>
. After you've confirmed the node
was registered successfully you can delete the copied teleport
binary.
Step 2/3. Generate an SSH client configuration
The next step is to configure your OpenSSH client to connect to your sshd
host
using credentials managed by Teleport. This configuration will use your user's
Teleport-issued certificate to authenticate to the sshd
host. It will also
authenticate the sshd
host using the host certificate you generated earlier.
First, make sure you have logged in to your Teleport cluster:
tsh status> Profile URL: https://teleport.example.com:443 Logged in as: myuser Cluster: teleport.example.com Roles: access, auditor, editor, host-certifier Logins: ubuntu, root Kubernetes: enabled Valid until: 2022-05-06 22:54:01 -0400 EDT [valid for 11h53m0s] Extensions: permit-agent-forwarding, permit-port-forwarding, permit-pty
tsh status> Profile URL: https://teleport.example.com:443 Logged in as: myuser Cluster: teleport.example.com Roles: access, auditor, editor, reviewer, host-certifier Logins: ubuntu, root Kubernetes: enabled Valid until: 2022-05-06 22:54:01 -0400 EDT [valid for 11h53m0s] Extensions: permit-agent-forwarding, permit-port-forwarding, permit-pty
tsh status> Profile URL: https://mytenant.teleport.sh:443 Logged in as: myuser Cluster: mytenant.teleport.sh Roles: access, auditor, editor, reviewer, host-certifier Logins: ubuntu, root Kubernetes: enabled Valid until: 2022-05-06 22:54:01 -0400 EDT [valid for 11h53m0s] Extensions: permit-agent-forwarding, permit-port-forwarding, permit-pty
On your local machine, run the following tsh
command. This will print a
configuration block that tells your SSH client to use credentials managed by
Teleport to connect to hosts in your cluster.
tsh config > ssh_config_teleport
This command creates an SSH configuration file at a nonstandard location in
order to make it easier to clean up, but you can append the output of
tsh config
to the default SSH config file (~/.ssh/config
) if you wish.
Teleport implements an SSH server that includes several subsystems, or
predefined commands that are run when the server handles a connection. The Proxy
Service implements a proxy
subsystem that forwards SSH traffic to remote hosts
and trusted clusters.
Here is a brief explanation of the configuration that tsh config
generates:
# Common flags for all {{ .ClusterName }} hosts
Host *.{{ .ClusterName }} {{ .ProxyHost }}
UserKnownHostsFile "{{ .KnownHostsPath }}"
IdentityFile "{{ .IdentityFilePath }}"
CertificateFile "{{ .CertificateFilePath }}"
If the host you are ssh
ing into belongs to your Teleport cluster (i.e., its
address is a subdomain of your cluster's domain), use a Teleport-managed known
hosts file, private key, and certificate that are stored in the .tsh
directory.
# Flags for all {{ .ClusterName }} hosts except the proxy
Host *.{{ .ClusterName }} !{{ .ProxyHost }}
Port 3022
ProxyCommand "{{ .TSHPath }}" proxy ssh --cluster={{ .ClusterName }} --proxy={{ .ProxyHost }} %r@%h:%p
If the host that you are ssh
ing into belongs to your Teleport cluster, the
OpenSSH client will first execute a command, the ProxyCommand
, that
establishes an SSH connection to the Proxy Service. This command,
tsh proxy ssh
, requests the proxy
subsystem in order to forward SSH traffic
through the Proxy Service to your chosen host (including a host in a Trusted
Cluster).
The tsh proxy ssh
command requests the proxy
subsystem through a command
similar to the following, which assumes you are logging in to a node called
mynode
as root
with a cluster called teleport.example.com
:
/usr/bin/ssh -l root -A -o UserKnownHostsFile=/root/.tsh/known_hosts -p 11105 teleport.example.com -s proxy:mynode:[email protected]
Notice that the known_hosts
file used by the command is managed by tsh
.
Since the sshd
host's information is listed in this file, your SSH client can
authenticate the host via the certificate we generated earlier.
If using PowerShell on Windows, note that normal shell redirection may write the file with the incorrect encoding. To ensure it's written properly, try the following:
tsh.exe config | out-file .ssh\config -encoding utf8 -append
Routing in Teleport clusters is case-sensitive by default, but OpenSSH always lowercases hostnames. If you
are using an OpenSSH client and have hosts with uppercase letters in their hostnames, you may need to set
case_insensitive_routing: true
in either the auth_service
block of your Teleport config, or in the
cluster_networking_config
resource.
If you switch between multiple Teleport Proxy Servers, you'll need to re-run
tsh config
for each to generate the cluster-specific configuration.
Similarly, if trusted clusters are added or removed, be sure to re-run
tsh config
and replace the previous configuration.
Step 3/3. Connect to your sshd
host
Once you have appended the new text to your OpenSSH client configuration file,
you can log in to your sshd
host using the configuration we generated earlier.
First, define environment variables for the address of your Teleport cluster,
the username you will use to log in to your sshd
host, and the port on your
sshd
host you are using for SSH traffic:
See the available logins you can use to access your sshd host
tsh status | grep LoginsLogins: ubuntu, rootUSER=ubuntuCLUSTER=teleport.example.comPORT=22
See the available logins you can use to access your sshd host
tsh status | grep LoginsLogins: ubuntu, rootUSER=ubuntuCLUSTER=mytenant.teleport.shPORT=22
Next, SSH in to your remote host:
ssh -p ${PORT?} -F ssh_config_teleport "${USER?}@${ADDR?}.${CLUSTER?}"
This name does not need to be resolvable via DNS as the connection will be routed through your Teleport Proxy Service.
By default, the OpenSSH client configuration generated by tsh config
directs
the Teleport Proxy Service to dial port 3022 of a node in your Teleport cluster.
This works if the node's SSH Service is listening on port 3022, and means that
you can connect to the Teleport SSH Service via your OpenSSH client.
When you join a Teleport node to a cluster, the node creates a reverse tunnel
to the cluster's Proxy Service. When you run an ssh
command to access a host
in your Teleport cluster using the configuration we generated, the Teleport
Proxy Service will attempt to connect to the host via this reverse tunnel and,
if that fails, try directly dialing the address.
In our case, the sshd
host is not running Teleport, so no reverse tunnel will
exist. Instead, the Proxy Service will establish a direct connection on the
host's SSH port.
You can log in to a host in a trusted leaf cluster by placing the name of the leaf cluster between the name of the node and the name of the root cluster:
ssh -F ssh_config_teleport ${USER?}@node2.leafcluster.${CLUSTER}
Teleport uses OpenSSH certificates instead of keys. When you connect to a
remote host, OpenSSH verifies that the address of the host is listed under the
Principals
section of the OpenSSH certificate. Usually, this is a fully
qualified domain name, rather than an IP address.