MongoDB SSH

Last reviewed: over 3 years ago

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.

Follow these instructions to set up Cloudflare Access in your account.
In Zero Trust ↗, go to Access > Applications.
Select Add an application and choose Self-hosted.
Create an application for a subdomain where users will connect to your deployment. Select Next.
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.
Select 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 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.

Once you select 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.

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.

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, refer to the list of useful terms.

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.

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MongoDB SSH

Configure Cloudflare Access

Configure the Kubernetes deployment

Configure Cloudflare Tunnel

Create a Tunnel

Delete the cert.pem file

Configure Cloudflare Tunnel

Connect from a client

Delete the `cert.pem` file