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secondary-config.md

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Secondary HAProxy config file

The ingress controller supports loading a secondary HAProxy configuration file where you can define additional sections such as resolvers, cache, etc

The main configuration file, haproxy.cfg, which is generated by the ingress controller, reflects the state of services and ingress resources within your Kubernetes cluster. The secondary configuration file is loaded alongside it, but remains completely under your control.

There are two main reasons to use the secondary configuration file:

  • Configure anything not supported by Ingress Controller annotations
  • Provide a stepping stone for migrating a legacy HAProxy config into one compatible with the HAProxy Kubernetes Ingress Controller.

The secondary HAProxy config is expected to be mounted in /etc/haproxy/haproxy-aux.cfg and Ingress Controller will monitor this file and reload haproxy when the file is updated.

Example: DNS runtime resolution

In the following example, we define a secondary config file in order to configure runtime DNS resolution in HAProxy by creating a resolvers section named mydns.
DNS resolution at Runtime can be useful to handle kubernetes services of type ExternalName or any other context where you want to target services by their DNS name.

Loading config file

First, create a file named /tmp/haproxy-aux.cfg in your local system and add a resolvers section to it, as shown in the following example configuration:

resolvers mydns          
  nameserver local 127.0.0.1:53
  nameserver google 8.8.8.8:53

Next, load the file into a ConfigMap:

$ kubectl create configmap haproxy-aux-cfg --from-file /tmp/haproxy-aux.cfg

configmap/haproxy-aux-cfg created

Then mount the ConfigMap as a volume in the ingress controller pod by editing the pod YAML installation manifest to add volumeMounts and volumes.
The target mount location should be /etc/haproxy/haproxy-aux.cfg :

containers:
  - name: haproxy-ingress             
    image: haproxytech/kubernetes-ingress:latest
    volumeMounts:
      - name: haproxy-cfg-vol
          mountPath: /etc/haproxy/haproxy-aux.cfg
  volumes:
    - name: haproxy-cfg-vol
        configMap:
          name: haproxy-aux-cfg

The resolvers section can then be referenced for example in the haproxy default-server directive via a backend-config-snippet:

backend-config-snippet: default-server init-addr none resolvers mydns

This sets the default DNS resolution behavior for resolving the IP addresses of backend services:

  • They should start in a down state without any valid IP.
  • They should use resolvers from the mydns section.

Updating config file

If you want to update the secondary config you will need to:

  1. Edit the config file
  2. Replace the ConfigMap:
$ kubectl create configmap haproxy-aux-cfg --from-file /tmp/haproxy-aux.cfg -o yaml --dry-run | kubectl replace -f -
configmap/haproxy-aux-cfg replaced

After few seconds kubernetes will notice the updated ConfigMap and updates the mounted volume accordingly which will make Ingress Controller reload haproxy to take into account the new config file.