DUP: allow to customize Erlang clustering on k8s

Introduce two configuration options for the formation of DUP
clusters on k8s. They can be set via two env vars:
- `DATA_UPDATER_PLANT_CLUSTERING_KUBERNETES_SELECTOR`,
  defaulting to `app=astarte-data-updater-plant`
- `DATA_UPDATER_PLANT_CLUSTERING_KUBERNETES_NAMESPACE`,
  defaulting to `astarte`

Signed-off-by: Arnaldo Cesco <arnaldo.cesco@secomind.com>

Author: Annopaolo

CHANGELOG.md

@@ -16,6 +16,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
   allowing to autoscale the service. This is done via Erlang clustering, so
   the `DATA_UPDATER_PLANT_CLUSTERING_STRATEGY` env var (default `none`) has
   been introduced to set clustering strategy.
+- [astarte_data_updater_plant] allow to configure Erlang clustering when using
+  the `kubernetes` option via `DATA_UPDATER_PLANT_CLUSTERING_KUBERNETES_SELECTOR`
+  and `DATA_UPDATER_PLANT_CLUSTERING_KUBERNETES_NAMESPACE`.
 
 ## [1.2.1] - Unreleased
 ### Changed

apps/astarte_data_updater_plant/lib/astarte_data_updater_plant/config.ex

@@ -245,6 +245,22 @@ defmodule Astarte.DataUpdaterPlant.Config do
           type: Astarte.DataUpdaterPlant.ClusteringStrategy,
           default: "none"
 
+  @envdoc "The Kubernetes selector to use when `kubernetes` Erlang clustering strategy is used. Defaults to `app=astarte-data-updater-plant`."
+  app_env :clustering_kubernetes_selector,
+          :astarte_data_updater_plant,
+          :clustering_kubernetes_selector,
+          os_env: "DATA_UPDATER_PLANT_CLUSTERING_KUBERNETES_SELECTOR",
+          type: :binary,
+          default: "app=astarte-data-updater-plant"
+
+  @envdoc "The Kubernetes namespace to use when `kubernetes` Erlang clustering strategy is used. Defaults to `astarte`."
+  app_env :clustering_kubernetes_namespace,
+          :astarte_data_updater_plant,
+          :clustering_kubernetes_namespace,
+          os_env: "DATA_UPDATER_PLANT_CLUSTERING_KUBERNETES_NAMESPACE",
+          type: :binary,
+          default: "astarte"
+
   # Since we have one channel per queue, this is not configurable
   def amqp_consumer_channels_per_connection_number!() do
     ceil(data_queue_total_count!() / amqp_consumer_connection_number!())
@@ -449,8 +465,8 @@ defmodule Astarte.DataUpdaterPlant.Config do
             config: [
               mode: :ip,
               kubernetes_node_basename: "astarte_data_updater_plant",
-              kubernetes_selector: "app=astarte-data-updater-plant",
-              kubernetes_namespace: "astarte",
+              kubernetes_selector: clustering_kubernetes_selector!(),
+              kubernetes_namespace: clustering_kubernetes_namespace!(),
               polling_interval: 10_000
             ]
           ]