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MongoDB SSH

You can build Zero Trust rules to secure connections to MongoDB deployments using Cloudflare Access and Cloudflare Tunnel. Cloudflare Tunnel requires a lightweight daemon, cloudflared, running alongisde the deployment and as on the client side.

In this tutorial, a client running cloudflared connects over SSH to a MongoDB deployment running on Kubernetes. The deployment example is structured to connect Compass to the MongoDB instance. The MongoDB Kubernetes deployment runs both the MongoDB database service and cloudflared as a ingress service that operates like a jump host.

🗺️ This tutorial covers how to:

  • Create a Cloudflare Access rule to secure a MongoDB deployment
  • Configure a StatefulSet and service definition for the deployment
  • Configure an Cloudflare Tunnel connection to Cloudflare's edge
  • Create an SSH configuration file for the client

⏲️ Time to complete:

50 minutes


Configure Cloudflare Access

You can build a rule in Cloudflare Access to control who can connect to your MongoDB deployment. Cloudflare Access rules are built around a hostname; even though this deployment will be accessible over SSH, the resource will be represented in Cloudflare as a hostname. For example, if you have the website app.com in your Cloudflare account, you can build a rule to secure mongodb.app.com.

First, follow these instructions to set up Cloudflare Access in your account.

Next, navigate to the Applications page in the Access section of the Cloudflare for Teams dashboard.

Apps

Click Add an application and choose Self-hosted.

Apps

Create an application for a subdomain where users will connect to your deployment. Click Next.

Apps

Build a rule to determine who can reach the deployment. You can build a rule that allows anyone in your organization to connect or you can build more granular rules based on signals like identity provider groups, multifactor method, or country.

Apps

Click Next again and add the application.

Configure the Kubernetes deployment

To be accessible over SSH, the Kubernetes deployment should manage both the MongoDB standalone service and an SSH proxy service. The configuration below will deploy 1 replica of the database service, available at port 27017, as well as an SSH proxy available at port 22.

StatefulSet Configuration
apiVersion: apps/v1
kind: StatefulSet
metadata:
name: mongodb-standalone
namespace: mongodb
spec:
serviceName: database
replicas: 1
selector:
matchLabels:
app: database
template:
metadata:
labels:
app: database
selector: mongodb-standalone
spec:
containers:
- name: mongodb-standalone
image: mongo
command: ["mongod"]
args: ["--config=/config/mongod.conf"]
ports:
- containerPort: 27017
protocol: TCP
name: mongod
volumeMounts:
- name: mongodb-conf
mountPath: /config
readOnly: true
- name: mongodb-data
mountPath: /data/db
- name: tls
mountPath: /etc/tls
- name: mongodb-socket
mountPath: /socket
- name: ssh-proxy
image: ubuntu:20.04
command: ["/scripts/entrypoint.sh"]
ports:
- containerPort: 22
protocol: TCP
name: ssh-port
volumeMounts:
- name: mongodb-socket
mountPath: /socket
- name: scripts
mountPath: /scripts
readOnly: true
- name: ssh-authorized-keys
mountPath: /config/ssh
readOnly: true
resources:
requests:
cpu: 20m
memory: 32Mi
volumes:
- name: mongodb-socket
emptyDir: {}
- name: mongodb-conf
configMap:
name: mongodb-standalone
items:
- key: mongod.conf
path: mongod.conf
- name: tls
secret:
secretName: tls
- name: mongodb-data
persistentVolumeClaim:
claimName: mongodb-standalone
- name: scripts
configMap:
name: scripts
items:
- key: entrypoint.sh
path: entrypoint.sh
mode: 0744
- name: ssh-authorized-keys
configMap:
name: ssh-proxy-config
items:
- key: authorized_keys
path: authorized_keys
mode: 0400

The corresponding service definition should also specify the the ports and target ports for the containers (in this case, the database service and the SSH proxy service).

Service Definition
apiVersion: v1
kind: Service
metadata:
name: database
namespace: mongodb
labels:
app: database
spec:
clusterIP: None
selector:
app: database
ports:
- protocol: TCP
port: 27017
targetPort: 27017
---
apiVersion: v1
kind: Service
metadata:
name: ssh-proxy
namespace: mongodb
labels:
app: database
spec:
selector:
app: database
ports:
- protocol: TCP
port: 22
targetPort: 22

The MongoDB pod and the SSH jump host will share a Unix socket over an empty directory volume. The entrypoint.sh file run by the jump host, example below, will start an OpenSSH server.

#!/bin/sh
export TZ=America/Chicago
ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone
apt-get update -y && apt-get install -y openssh-server
mkdir /root/.ssh
cp /config/ssh/authorized_keys /root/.ssh/authorized_keys
chmod 400 /root/.ssh/authorized_keys
service ssh start
while true;
do sleep 30;
done;

Configure Cloudflare Tunnel

Next, you can use cloudflared to connect to Cloudflare's Edge using Cloudflare Tunnel. Start by downloading and installing the Cloudflare Tunnel daemon, cloudflared.

Once installed, run the following command to authenticate the instance of cloudflared into your Cloudflare account.

$ cloudflared login

The command will launch a browser window and prompt you to login with your Cloudflare account. Choose a website that you have added into your account.

Choose Site

Once you click one of the sites in your account, Cloudflare will download a certificate file, called cert.pem to authenticate this instance of cloudflared. The cert.pem file uses a certificate to authenticate your instance of cloudflared and includes an API key for your account to perform actions like DNS record changes.

You can now use cloudflared to control Cloudflare Tunnel connections in your Cloudflare account.

Download Cert

Create a Tunnel

You can now create a Tunnel that will connect cloudflared to Cloudflare's edge. You'll configure the details of that Tunnel in the next step.

Run the following command to create a Tunnel. You can replace mongodb with any name that you choose. This command requires the cert.pem file.

$ cloudflared tunnel create mongodb

Cloudflare will create the Tunnel with that name and generate an ID and credentials file for that Tunnel.

New Tunnel

Delete the cert.pem file

The credentials file is separate from the cert.pem file. Unlike the cert.pem file, the credentials file consists of a token that authenticates only the Named Tunnel you just created. Formatted as JSON, the file cannot make changes to your Cloudflare account or create additional Tunnels.

If you are done creating Tunnels, you can delete the cert.pem file, leave only the credentials file, and continue to manage DNS records directly in the Cloudflare dashboard or API. For additional information on the different functions of the two files, see the table in this section.

Store the JSON file as a Kubernetes secret.

Configure Cloudflare Tunnel

The previous setps used cloudflared to generate a credentials file for your Cloudflare account. When run as a service alongside the MongoDB Kubernetes deployment you will need to use a Docker image of cloudflared. Cloudflare makes an official image available in DockerHub.

The configuration below will run a single replica of cloudflared as an ingress point alongside the MongoDB and SSH proxy services. cloudflared will proxy traffic to the SSH proxy service. The cloudflared instance will run as its own deployment in a different namespace and, if network policy allows, ingress to any service in the Kubernetes node.

`cloudflared` Configuration
apiVersion: apps/v1
kind: Deployment
metadata:
name: dashboard-tunnel
namespace: argotunnel
labels:
app: dashboard-tunnel
spec:
replicas: 1
selector:
matchLabels:
app: dashboard-tunnel
template:
metadata:
labels:
app: dashboard-tunnel
spec:
containers:
- name: dashboard-tunnel
# Image from https://hub.docker.com/r/cloudflare/cloudflared
image: cloudflare/cloudflared:2020.11.11
command: ["cloudflared", "tunnel"]
args: ["--config", "/etc/tunnel/config.yaml", "run"]
ports:
- containerPort: 5000
livenessProbe:
tcpSocket:
port: 5000
initialDelaySeconds: 60
periodSeconds: 60
volumeMounts:
- name: dashboard-tunnel-config
mountPath: /etc/tunnel
- name: tunnel-credentials
mountPath: /etc/credentials
volumes:
- name: dashboard-tunnel-config
configMap:
name: dashboard-tunnel-config
- name: tunnel-credentials
secret:
secretName: tunnel-credentials
---
apiVersion: v1
kind: ConfigMap
metadata:
name: dashboard-tunnel-config
namespace: argotunnel
data:
config.yaml: |
tunnel: 9a00ef26-4997-4de2-83db-631efc74245c
credentials-file: /etc/credentials/k8s-dashboard.json
metrics: :5000
protocol: http2
no-autoupdate: true
ingress:
- hostname: mongodb.widgetcorp.tech
originRequest:
bastionMode: true
- service: http_status:404

Connect from a client

Once deployed, you can run cloudflared on the client side to connect to the MongoDB deployment. Add the following lines to your SSH configuration file, replacing the examples with your hostname and details. The --destination value should match the URL of the SSH Proxy service configured previously.

Host mongodb
ProxyCommand /usr/local/bin/cloudflared access ssh --hostname mongodb.widgetcorp.tech --destination ssh-proxy.mongodb.svc.cluster.local:22
LocalForward 27000 /socket/mongodb-27017.sock
User root
IdentityFile /Users/username/.ssh/id_rsa

This is a one-time step. When you next attempt to make an SSH connection to the deployment, cloudflared will launch a browser window and prompt you to authenticate. Once authenticated, you will be connected if you have a valid session. Once the tunnel is established, all requests to localhost:27000 on your machine will be forwarded to /socket/mongodb-27017.sock on the SSH proxy container.

You can then set MongoDB Compass to connect to localhost:27000.

Compass Config