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.