Registering Agentless OpenSSH Servers with IaC

In this guide, you will see how to register in Teleport your OpenSSH nodes through infrastructure as code (IaC). Teleport supports three ways to dynamically create resources from code:

• The Teleport Kubernetes Operator, which allows you to manage Teleport resources from Kubernetes
• The Teleport Terraform Provider, which allows you to manage Teleport resources via Terraform
• The tctl CLI, which allows you to manage Teleport resources from your local computer or your CI environment

Prerequisites

To follow this guide, you must have:

for operators deployed with the `teleport-cluster` Helm chart
export OPERATOR_NAMESPACE="teleport-cluster"

for standalone operators
export OPERATOR_NAMESPACE="teleport-iac"

• a server running OpenSSH you will add to the Teleport cluster. This server must be reachable from the proxy (public IP address and firewall allowing traffic on port 22).

Step 1/5 - Gather the required information

To register an OpenSSH server in Teleport you will need the following information:

• The server hostname: ssh-server-hostname
• The public server IP address with SSH port: 198.51.100.1:22

You must also choose a set of labels for the server. Those labels can be used to describe the server and control which users can access the server. They can be dynamically changed later, without having to reconfigure openSSH.

See the Access Controls for Servers page for more details about labels and how to control access to your servers.

In the rest of this guide, the labels will be:

env: test
team: engineering

Step 2/5 - Write the server manifest

In this step, we'll write text files describing the OpenSSH server resource we want to register in Teleport. Those files are called manifests and their syntax will vary based on the IaC tooling you'll use.

Those manifests are typically versioned in a shared revision system like git. This allows you to keep track of all changes, follow standard code review procedures before changing resources in Teleport, and quickly redeploy your Teleport instance if needed.

uuidgen

a100fdd0-52db-4eca-a7ab-c3afa7a1564a

uuidgen | tr '[:upper:]' '[:lower:]'

a100fdd0-52db-4eca-a7ab-c3afa7a1564a

New-guid
Guid----a100fdd0-52db-4eca-a7ab-c3afa7a1564a

kind: node
version: v2
sub_kind: openssh
metadata:
  name: a100fdd0-52db-4eca-a7ab-c3afa7a1564a  # this is the UUID previously generated
  labels:
    env: test
    team: engineering
spec:
  addr: 198.51.100.1:22
  hostname: ssh-server-hostname

uuidgen

a100fdd0-52db-4eca-a7ab-c3afa7a1564a

uuidgen | tr '[:upper:]' '[:lower:]'

a100fdd0-52db-4eca-a7ab-c3afa7a1564a

New-guid
Guid----a100fdd0-52db-4eca-a7ab-c3afa7a1564a

apiVersion: resources.teleport.dev/v1
kind: TeleportOpenSSHServerV2
metadata:
  name: a100fdd0-52db-4eca-a7ab-c3afa7a1564a  # this is the UUID previously generated
  # kubernetes CR labels are propagated to the Teleport resource
  labels:
    env: test
    team: engineering
spec:
  addr: 198.51.100.1:22
  hostname: ssh-server-hostname

resource "teleport_server" "openssh_agentless" {
  version = "v2"
  sub_kind = "openssh"
  // Name is not required for servers, this is a special case.
  // When a name is not set, an UUID will be generated by Teleport and
  // imported back into Terraform.
  spec = {
    addr = "198.51.100.1:22"
    hostname = "ssh-server-hostname"
  }
}

output "openssh_node_id" {
  value = teleport_server.openssh_agentless.metadata.name
}

Step 3/5. Apply all manifests

tctl create -f openssh-node-resource.yaml
node "a100fdd0-52db-4eca-a7ab-c3afa7a1564a" has been created

kubectl apply -n "$OPERATOR_NAMESPACE" -f openssh-node-resource.yaml
teleportopensshserverv2.resources.teleport.dev/a100fdd0-52db-4eca-a7ab-c3afa7a1564a created

kubectl get teleportopensshserverv2 -n "$OPERATOR_NAMESPACE"
NAME                                   AGE
a100fdd0-52db-4eca-a7ab-c3afa7a1564a   10m

terraform plan
Terraform will perform the following actions:
  # teleport_server.openssh_agentless will be created  + resource "teleport_server" "openssh_agentless" {      + id       = (known after apply)      + kind     = (known after apply)      + metadata = (known after apply)      + spec     = {          + addr     = "198.51.100.1:22"          + hostname = "ssh-server-hostname"        }      + sub_kind = "openssh"      + version  = "v2"    }
Plan: 1 to add, 0 to change, 0 to destroy.
Changes to Outputs:  + openssh_node_id = (known after apply)

terraform apply
[...]
Do you want to perform these actions?  Terraform will perform the actions described above.  Only 'yes' will be accepted to approve.
  Enter a value: yes
teleport_server.openssh_agentless: Creating...teleport_server.openssh_agentless: Creation complete after 3s [id=a100fdd0-52db-4eca-a7ab-c3afa7a1564a]
Apply complete! Resources: 1 added, 0 changed, 0 destroyed.
Outputs:
openssh_node_id = "a100fdd0-52db-4eca-a7ab-c3afa7a1564a"

Step 4/5. Validate the server created in Teleport

Now that the IaC tooling has run, we'll validate that Teleport is now aware of the OpenSSH server:

List nodes with a given hostname or IP address
tsh ls --search="ssh-server-hostname"
Node Name                                           Address        Labels--------------------- ------------ --------------- --------------------------ssh-server-hostname 198.51.100.1:22 env=test,team=engineering
Get the node details by hostname
tctl get "node/ssh-server-hostname"

Get the node details by ID
tctl get node/a100fdd0-52db-4eca-a7ab-c3afa7a1564a

Step 5/5. Trust the Teleport CA and issue host certificates

At this point, Teleport is aware that there's an OpenSSH server and knows how to contact it and which user should have access. However, neither Teleport nor the server trust each other.

You need to configure the server to trust connections coming from Teleport (trust the Teleport SSH Certificate Authority), and you need to give the server an SSH Host certificate issued by Teleport.

Those steps can be automated, but the automation will depend on your custom infrastructure and tooling (you can configure the SSH CA in the VM image, use custom startup scripts, provision servers with Ansible, ...).

A step-by-step manual setup is described in the OpenSSH manual installation guide starting with the Step 2.

Next steps

• Setup RBAC to control which user can SSH on which server.