Kubernetes pod as a Bastion Host

In Cloud Native apps private networks, databases and services are a reality.

An infrastructure can be fully private and only a limited number of entry points can be available.

Obviously the more restricted the better.

Still there are cases where there has not been any infrastructure setup for the private services and ways to link towards them. however if there is access through Kubernetes, HAProxy can help.

HAProxy can accept a configuration file. Uploading that file as a configmap and then mount the configmap to a Kubernetes pod will be easy. Then the HAProxy Kubernetes pod will be able to spin up using that configuration and thus establish a proxy connection.

Let’s start with the ha-proxy configuration. The target would be a MySQL database with a private IP.

 
apiVersion: v1
data:
  haproxy.cfg: |-
    global
    defaults
        timeout client          30s
        timeout server          30s
        timeout connect         30s

    frontend frontend
        bind    0.0.0.0:3306
        default_backend backend

    backend backend
        mode                    tcp
        server upstream 10.0.1.7:3306
kind: ConfigMap
metadata:
  creationTimestamp: null
  name: mysql-haproxy-port-forward

On the upstream we just add the ip and the port of the db, on the frontend we specify the local port and address we shall use.

By doing the above we have a way to mount the config file to our Kubernetes pod.

Now let’s create the pod

 
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: mysql-forward-pod
  name: mysql-forward-pod
spec:
  containers:
    - command:
      - haproxy
      - -f
      - /usr/local/etc/haproxy/haproxy.cfg
      - -V
      image: haproxy:1.7-alpine
      name: mysql-forward-pod
      resources: {}
      volumeMounts:
        - mountPath: /usr/local/etc/haproxy/
          name: mysql-haproxy-port-forward
  dnsPolicy: ClusterFirst
  restartPolicy: Always
  volumes:
    - name: mysql-haproxy-port-forward
      configMap:
        name: mysql-haproxy-port-forward
status: {}

On the volume section we set the configmap as a volume. On the container section we mount the configmap to a path thus having access to the file.
We use a HAProxy image, and we provide the command to start HAProxy using the file we mounted before.

To test that it works, use a kubectl session that has port-forward permissions and do

 
kubectl port-forward  mysql-forward-pod 3306:3306

You shall be able to access mysql from your localhost.