grafana: add dynamic prometheus datasource

jobs/monitoring/grafana.hcl

@@ -48,11 +48,11 @@ job "grafana" {
         ports = ["http"]
 
         volumes = [
-          "/storage/nomad/${NOMAD_JOB_NAME}/${NOMAD_TASK_NAME}:/var/lib/grafana"
+          "/storage/nomad/${NOMAD_JOB_NAME}/${NOMAD_TASK_NAME}:/var/lib/grafana",
+          "local/datasources.yml:/etc/grafana/provisioning/datasources/datasources.yml"
         ]
       }
 
-
       template {
         data        = <<EOH
 GF_DATABASE_TYPE=postgres
@@ -66,6 +66,21 @@ EOH
         destination = "local/.env"
         env         = true
       }
+      template {
+        data        = <<EOH
+apiVersion: 1
+
+datasources:
+  - name: Prometheus
+    type: prometheus
+    access: proxy
+    {{- range service "prometheus" }}
+    url: http://prometheus.service.consul:{{ .Port }}{{ end }}
+    isDefault: true
+    editable: false
+EOH
+        destination = "local/datasources.yml"
+      }
     }
     task "db" {
       driver = "docker"