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.

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