Avoid environment variable for default setting on k8s

Using environment variable make it harder to override the settings,
since only replacing the environment variable will work, configuration
files have less priority.

Only account_id and registration_key are still environment variables to
avoid breaking compatibility (some user already override the bleemeo-credentials
with their own value for those environment variables, converting them to
configuration file won't be transparent for them).

Author: PierreF

k8s.yaml

@@ -7,11 +7,24 @@ metadata:
   name: glouton-credentials
 type:
 stringData:
+  # ${VARIABLE} are expected to be replaced by envsubt before the YAML is used by kubectl.
+  # For example doing "curl -s https://packages.bleemeo.com/bleemeo-agent/kubernetes/k8s.yaml | envsubst | kubectl apply -f -"
   GLOUTON_BLEEMEO_ACCOUNT_ID: ${GLOUTON_BLEEMEO_ACCOUNT_ID}
   GLOUTON_BLEEMEO_REGISTRATION_KEY: ${GLOUTON_BLEEMEO_REGISTRATION_KEY}
 ---
 apiVersion: v1
 kind: ConfigMap
+metadata:
+  name: glouton-default-config
+data:
+  10-default.conf: |
+    # Avoid modifying this config. Modify the glouton-config present below, and we recommend using
+    # another YAML file (see comment below).
+    kubernetes:
+      clustername: "${GLOUTON_KUBERNETES_CLUSTERNAME}"
+---
+apiVersion: v1
+kind: ConfigMap
 metadata:
   name: glouton-config
 data:
@@ -25,6 +38,25 @@ data:
     # Note: it's not a typo. The "-,./glouton-custom.yaml" is correct: we read from stdin ("-") then from the file.
 ---
 apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: glouton-environment
+data:
+  # This configmap allow to set environment variable to configure Glouton,
+  # to use Glouton configuration files, see glouton-config above.
+  #
+  # We recommend using another Kubernetes YAML file to make change of glouton-environment.
+  # This will allow to use latest version of this k8s.yaml file without needs to merge your
+  # local change in the newer version.
+  # Example: have another file "glouton-custom.yaml" which only contains a glouton-environment ConfigMap
+  # then apply with:
+  # curl -s https://packages.bleemeo.com/bleemeo-agent/kubernetes/k8s.yaml | envsubst | kubectl apply -f -,./glouton-custom.yaml
+  # Note: it's not a typo. The "-,./glouton-custom.yaml" is correct: we read from stdin ("-") then from the file.
+  #
+  # Example of settings:
+  # GLOUTON_BLEEMEO_INITIAL_AGENT_NAME: my_name
+---
+apiVersion: v1
 kind: ServiceAccount
 metadata:
   name: glouton
@@ -125,15 +157,15 @@ spec:
           value: "/etc/glouton/glouton.conf,/etc/glouton/glouton-k8s-default.conf,/etc/glouton/conf.d,/etc/glouton/conf-k8s.d"
         - name: GLOUTON_KUBERNETES_ENABLE
           value: "True"
-        - name: GLOUTON_KUBERNETES_CLUSTERNAME
-          value: "${GLOUTON_KUBERNETES_CLUSTERNAME}"
         - name: GLOUTON_KUBERNETES_NODENAME
           valueFrom:
             fieldRef:
               fieldPath: spec.nodeName
         envFrom:
         - secretRef:
             name: glouton-credentials
+        - configMapRef:
+            name: glouton-environment
         resources:
           requests:
             cpu: 0.05
@@ -147,5 +179,9 @@ spec:
         hostPath:
           path: /
       - name: glouton-config
-        configMap:
-          name: glouton-config
+        projected:
+          sources:
+            - configMap:
+                name: glouton-default-config
+            - configMap:
+                name: glouton-config