Single dashboards upd (#1593)

* dasbhoard: replace `null` datasources

null datasource value may confuse Grafana and make it drop panel query in some
versions.

* docker: bump grafana image version

* dashboards: add URL variable selector to vmagent dashboard

* dashboards: add new panel `Remote write connection saturation` to vmagent dashboard

* alerts: add new alert for `Remote write connection saturation` panel of vmagent dashboard

* dashboards: add "Logging rate" panel to vmagent dashboard

dashboards/victoriametrics.json

@@ -91,7 +91,7 @@
       "id": 6,
       "panels": [
         {
-          "datasource": null,
+          "datasource": "$ds",
           "description": "",
           "gridPos": {
             "h": 2,
@@ -373,7 +373,7 @@
           "type": "stat"
         },
         {
-          "datasource": null,
+          "datasource": "$ds",
           "fieldConfig": {
             "defaults": {
               "color": {

deployment/docker/alerts.yml

@@ -248,3 +248,16 @@ groups:
           description: "Vmagent fails to push data via remote write protocol to destination \"{{ $labels.url }}\"\n
             Ensure that destination is up and reachable."
 
+      - alert: RemoteWriteConnectionIsSaturated
+        expr: rate(vmagent_remotewrite_send_duration_seconds_total[5m]) > 0.9
+        for: 15m
+        labels:
+          severity: warning
+        annotations:
+          dashboard: "http://localhost:3000/d/G7Z9GzMGz?viewPanel=84&var-instance={{ $labels.instance }}"
+          summary: "Remote write connection from \"{{ $labels.job }}\" (instance {{ $labels.instance }}) to {{ $labels.url }} is saturated"
+          description: "The remote write connection between vmagent \"{{ $labels.job }}\" (instance {{ $labels.instance }}) and destination \"{{ $labels.url }}\"
+            is saturated by more than 90% and vmagent won't be able to keep up.\n
+            This usually means that `-remoteWrite.queues` command-line flag must be increased in order to increase
+            the number of connections per each remote storage."
+

deployment/docker/docker-compose.yml

@@ -39,7 +39,7 @@ services:
     restart: always
   grafana:
     container_name: grafana
-    image: grafana/grafana:8.0.0
+    image: grafana/grafana:8.1.2
     depends_on:
       - "victoriametrics"
     ports: