Allow prometheus metrics collection

This patch adds a METRICS_ENABLED configuration variables which,
when switched on, defines a metrics entrypoint and enables the
built-in prometheus metrics exporter. This allows the monitoring
stack to collect and show traefik metrics

.env.sample

@@ -53,6 +53,14 @@ COMPOSE_FILE="compose.yml"
 #COMPOSE_FILE="$COMPOSE_FILE:compose.keycloak.yml"
 #KEYCLOAK_MIDDLEWARE_ENABLED=1
 
+#####################################################################
+# Prometheus metrics                                                #
+#####################################################################
+
+## Enable prometheus metrics collection
+## used used by the coop-cloud monitoring stack
+#METRICS_ENABLED=1
+
 #####################################################################
 # Additional services                                               #
 #####################################################################

abra.sh

@@ -1,3 +1,3 @@
-export TRAEFIK_YML_VERSION=v11
+export TRAEFIK_YML_VERSION=v12
 export FILE_PROVIDER_YML_VERSION=v2
 export ENTRYPOINT_VERSION=v2

traefik.yml.tmpl

@@ -54,10 +54,20 @@ entrypoints:
   mumble-udp:
     address: ":64738/udp"
   {{ end }}
+  {{ if eq (env "METRICS_ENABLED") "1" }}
+  metrics:
+    address: ":8082"
+  {{ end }}
 
 ping:
   entryPoint: web
 
+{{ if eq (env "METRICS_ENABLED") "1" }}
+metrics:
+  prometheus:
+    entryPoint: metrics
+{{ end }}
+
 certificatesResolvers:
   staging:
     acme: