Automatically Discover GCP Compute Instances

The Teleport Discovery Service can connect to GCP and automatically discover and enroll GCP Compute Engine instances matching configured labels. It will then execute a script on these discovered instances that will install Teleport, start it and join the cluster.

Prerequisites

• A running Teleport cluster version 15.2.4 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 and tsh client tool.

  On Teleport Enterprise, you must use the Enterprise version of tctl, which you can download from your Teleport account workspace. Otherwise, visit Installation for instructions on downloading tctl and tsh for Teleport Community Edition.

• A GCP compute instance to run the Discovery Service on.
• GCP compute instances to join the Teleport cluster, running Ubuntu/Debian/RHEL if making use of the default Teleport install script. (For other Linux distributions, you can install Teleport manually.)
• To check that you can connect to your Teleport cluster, sign in with tsh login, then verify that you can run tctl commands using your current credentials. tctl is supported on macOS and Linux machines. For example:

  tsh login --proxy=teleport.example.com --user=[email protected]
  tctl status
  Cluster  teleport.example.com
  Version  15.2.4
  CA pin   sha256:abdc1245efgh5678abdc1245efgh5678abdc1245efgh5678abdc1245efgh5678

  If you can connect to the cluster and run the tctl status command, you can use your current credentials to run subsequent tctl commands from your workstation. If you host your own Teleport cluster, you can also run tctl commands on the computer that hosts the Teleport Auth Service for full permissions.

Step 1/6. Create a GCP invite token

When discovering GCP compute instances, Teleport makes use of GCP invite tokens for authenticating joining SSH Service instances.

Create a file called token.yaml:

# token.yaml
kind: token
version: v2
metadata:
  # the token name is not a secret because instances must prove that they are
  # running in your GCP project to use this token
  name: gcp-discovery-token
spec:
  # use the minimal set of roles required (e.g. Node, Proxy, App, Kube, DB, WindowsDesktop)
  roles: [Node]

  # set the join method allowed for this token
  join_method: gcp

  gcp:
    allow:
      # The GCP project ID(s) that VMs can join from.
      - project_ids: []
        # (Optional) The locations that VMs can join from. Note: both regions and
        # zones are accepted.
        locations: []
        # (Optional) The email addresses of service accounts that VMs can join
        # with.
        service_accounts: []

Add your instance's project ID(s) to the project_ids field. Add the token to the Teleport cluster with:

tctl create -f token.yaml

Step 2/6. Configure IAM permissions for Teleport

Create a service account that will give Teleport IAM permissions needed to discover instances.

• Console
• gcloud

Go to IAM > Roles in the GCP console and click + Create Role. Pick a name for the role (e.g. teleport-discovery) and give it the following permissions:

• compute.instances.get
• compute.instances.getGuestAttributes
• compute.instances.list
• compute.instances.setMetadata
• iam.serviceAccounts.actAs
• iam.serviceAccounts.get
• iam.serviceAccounts.list

Click Create.

Go to IAM > Service accounts and click + Create Service Account. Pick a name for the service account (e.g. teleport-discovery) and copy its email address to your clipboard. Click Create and Continue.

Go to IAM and click Grant Access. Paste the service account's email into the New principals field and select your custom role. Click Save.

Copy the following and paste it into a file called teleport-discovery-role.yaml:

# teleport-discovery-role.yaml
title: "teleport-discovery"
description: "A role to enable Teleport to discover GCP compute instances"
stage: "ALPHA"
includedPermissions:
- compute.instances.get
- compute.instances.getGuestAttributes
- compute.instances.list
- compute.instances.setMetadata
- iam.serviceAccounts.actAs
- iam.serviceAccounts.get
- iam.serviceAccounts.list

Then run the following command to create the role:

gcloud iam roles create teleport_discovery \--project=project_id \--file=teleport-discovery-role.yaml

Run the following command to create the service account:

gcloud iam service-accounts create teleport-discovery \--description="A service account to enable Teleport to discover GCP compute instances" \--display-name="teleport-discovery"

Run the following command to add the new role to the new service account:

gcloud projects add-iam-policy-binding project_id \--member="serviceAccount:teleport-discovery@project_id.iam.gserviceaccount.com" \--role="projects/project_id/roles/teleport_discovery"

Step 3/6. Configure instances to be discovered

Ensure that each instance to be discovered has a service account assigned to it. No permissions are required on the service account. To check if an instance has a service account, run the following command and confirm that there is at least one entry under serviceAccounts:

gcloud compute instances describe --format="yaml(name,serviceAccounts)" instance_name

Enable guest attributes on instances

Guest attributes (a subset of custom metadata used for infrequently updated data) must be enabled on instances to be discovered so Teleport can access their SSH host keys. Enable guest attributes by setting enable-guest-attributes to TRUE in the instance's metadata.

gcloud compute instances add-metadata instance_name \--metadata=enable-guest-attributes=True

If guest attributes are enabled during instance creation, the guest attributes will automatically be populated with the instance's host keys. If guest attributes were enabled after the instance was created, you can manually add the host keys to the guest attributes below:

#!/usr/bin/env bash
for file in /etc/ssh/ssh_host_*_key.pub; do
  read -r KEY_TYPE KEY _ <"$file"
  curl -X PUT --data "$KEY" "http://metadata.google.internal/computeMetadata/v1/instance/guest-attributes/hostkeys/$KEY_TYPE" -H "Metadata-Flavor: Google"
done

gcloud compute instances add-metadata instance_name \--metadata-from-file=startup-script="add-host-keys.sh"

gcloud compute ssh instance_name \--command='for file in /etc/ssh/ssh_host_*_key.pub; do KEY_TYPE=$(awk '\''{print $1}'\'' $file); KEY=$(awk '\''{print $2}'\''  $file); curl -X PUT --data "$KEY" "http://metadata.google.internal/computeMetadata/v1/instance/guest-attributes/hostkeys/$KEY_TYPE" -H "Metadata-Flavor: Google"; done'

Step 4/6. Install the Teleport Discovery Service

Install Teleport on the virtual machine that will run the Discovery Service.

Install Teleport on your Linux server:

1. Assign edition to one of the following, depending on your Teleport edition:

   Edition	Value
   Teleport Enterprise Cloud	cloud
   Teleport Enterprise (Self-Hosted)	enterprise
   Teleport Community Edition	oss

2. Get the version of Teleport to install. If you have automatic agent updates enabled in your cluster, query the latest Teleport version that is compatible with the updater:

   TELEPORT_DOMAIN=example.teleport.com
   TELEPORT_VERSION="$(curl https://$TELEPORT_DOMAIN/v1/webapi/automaticupgrades/channel/default/version | sed 's/v//')"

   Otherwise, get the version of your Teleport cluster:

   TELEPORT_DOMAIN=example.teleport.com
   TELEPORT_VERSION="$(curl https://$TELEPORT_DOMAIN/v1/webapi/ping | jq -r '.server_version')"

3. Install Teleport on your Linux server:

   curl https://goteleport.com/static/install.sh | bash -s ${TELEPORT_VERSION} edition

   The installation script detects the package manager on your Linux server and uses it to install Teleport binaries. To customize your installation, learn about the Teleport package repositories in the installation guide.

Step 5/6. Configure Teleport to discover GCP compute instances

If you are running the Discovery Service on its own host, the service requires a valid invite token to connect to the cluster. Generate one by running the following command against your Teleport Auth Service:

tctl tokens add --type=discovery

Save the generated token in /tmp/token on the virtual machine that will run the Discovery Service.

In order to enable GCP instance discovery the discovery_service.gcp section of teleport.yaml must include at least one entry:

version: v3
teleport:
  join_params:
    token_name: "/tmp/token"
    method: token
  proxy_server: "teleport.example.com:443"
auth_service:
  enabled: off
proxy_service:
  enabled: off
ssh_service:
  enabled: off
discovery_service:
  enabled: "yes"
  gcp:
    - types: ["gce"]
      # The IDs of GCP projects that VMs can join from.
      project_ids: []
      # (Optional) The locations that VMs can join from. Note: both regions and
      # zones are accepted.
      locations: []
      # (Optional) The email addresses of service accounts that VMs can join
      # with.
      service_accounts: []
      # (Optional) Labels that joining VMs must have.
      labels:
        "env": "prod" # Match virtual machines where label:env=prod
      installer:
        public_proxy_addr: "teleport.example.com:443"

• Edit the teleport.auth_server or teleport.proxy_server key to match your Auth Service or Proxy Service's domain name and port, respectively.
• Adjust the keys under discovery_service.gcp to match your GCP environment, specifically the projects, locations, service accounts, and tags you want to associate with the Discovery Service.

GCP credentials

The Teleport Discovery Service must have the credentials of the teleport-discovery GCP service account we created above in order to be able to log in.

The easiest way to ensure that is to run the Discovery Service on a GCP instance and assign the service account to that instance. Refer to Set Up Application Default Credentials for details on alternate methods.

Step 6/6. [Optional] Customize the default installer script

To customize the default installer script, execute the following command on your workstation:

tctl get installer/default-installer > teleport-default-installer.yaml

The resulting teleport-default-installer.yaml can be edited to change what gets executed when enrolling discovered instances.

After making the desired changes to the default installer, the resource can be updated by executing:

tctl create -f teleport-default-installer.yaml

Multiple installer resources can exist and be specified in the gcp.install.script_name section of a discovery_service.gcp list item in teleport.yaml:

discovery_service:
  gcp:
    - types: ["gce"]
      tags:
       - "env": "prod"
      install: # optional section when default-installer is used.
        script_name: "default-installer"
    - types: ["gce"]
      tags:
       - "env": "devel"
      install:
        script_name: "devel-installer"

The installer resource has the following templating options:

• {{ .MajorVersion }}: the major version of Teleport to use when installing from the repository.
• {{ .PublicProxyAddr }}: the public address of the Teleport Proxy Service to connect to.
• {{ .RepoChannel }}: Optional package repository (apt/yum) channel name. Has format <channel>/<version> e.g. stable/v15. See installation for more details.
• {{ .AutomaticUpgrades }}: indicates whether Automatic Updates are enabled or disabled. Its value is either true or false. See self-hosted automatic agent updates for more information.
• {{ .TeleportPackage }}: the Teleport package to use. Its value is either teleport-ent or teleport depending on whether the cluster is enterprise or not.

These can be used as follows:

kind: installer
metadata:
  name: default-installer
spec:
  script: |
    echo {{ .PublicProxyAddr }}
    echo Teleport-{{ .MajorVersion }}
    echo Repository Channel: {{ .RepoChannel }}
version: v1

Which, when retrieved for installation, will evaluate to a script with the following contents:

echo teleport.example.com
echo Teleport-15.2.4
echo Repository Channel: stable/v15.2.4

The default installer will take the following actions:

• Add an official Teleport repository to supported Linux distributions.
• Install Teleport via apt or yum.
• Generate the Teleport config file and write it to /etc/teleport.yaml.
• Enable and start the Teleport service.

Next steps

• Read Joining Services via GCP for more information on GCP tokens.
• Full documentation on GCP discovery configuration can be found through the config file reference documentation.
• The complete default installer can be found with the Teleport source .