Add schema to DNS service discovery docs

The missing schema leads to errors like `improperly formatted alertmanager URL "alertmanager.mimir.svc.cluster.local:8080/alertmanager" (maybe the scheme is missing?)`.

cmd/mimir/config-descriptor.json

@@ -7366,7 +7366,7 @@
           "kind": "field",
           "name": "alertmanager_url",
           "required": false,
-          "desc": "Comma-separated list of URL(s) of the Alertmanager(s) to send notifications to. Each URL is treated as a separate group. Multiple Alertmanagers in HA per group can be supported by using DNS service discovery format. Basic auth is supported as part of the URL.",
+          "desc": "Comma-separated list of URL(s) of the Alertmanager(s) to send notifications to. Each URL is treated as a separate group. Multiple Alertmanagers in HA per group can be supported by using DNS service discovery format, comprehensive of the scheme. Basic auth is supported as part of the URL.",
           "fieldValue": null,
           "fieldDefaultValue": "",
           "fieldFlag": "ruler.alertmanager-url",

cmd/mimir/help-all.txt.tmpl

@@ -1616,7 +1616,7 @@ Usage of ./cmd/mimir/mimir:
   -ruler.alertmanager-refresh-interval duration
     	How long to wait between refreshing DNS resolutions of Alertmanager hosts. (default 1m0s)
   -ruler.alertmanager-url string
-    	Comma-separated list of URL(s) of the Alertmanager(s) to send notifications to. Each URL is treated as a separate group. Multiple Alertmanagers in HA per group can be supported by using DNS service discovery format. Basic auth is supported as part of the URL.
+    	Comma-separated list of URL(s) of the Alertmanager(s) to send notifications to. Each URL is treated as a separate group. Multiple Alertmanagers in HA per group can be supported by using DNS service discovery format, comprehensive of the scheme. Basic auth is supported as part of the URL.
   -ruler.client.backoff-max-period duration
     	Maximum delay when backing off. (default 10s)
   -ruler.client.backoff-min-period duration

cmd/mimir/help.txt.tmpl

@@ -508,7 +508,7 @@ Usage of ./cmd/mimir/mimir:
   -ruler.alertmanager-client.basic-auth-username string
     	HTTP Basic authentication username. It overrides the username set in the URL (if any).
   -ruler.alertmanager-url string
-    	Comma-separated list of URL(s) of the Alertmanager(s) to send notifications to. Each URL is treated as a separate group. Multiple Alertmanagers in HA per group can be supported by using DNS service discovery format. Basic auth is supported as part of the URL.
+    	Comma-separated list of URL(s) of the Alertmanager(s) to send notifications to. Each URL is treated as a separate group. Multiple Alertmanagers in HA per group can be supported by using DNS service discovery format, comprehensive of the scheme. Basic auth is supported as part of the URL.
   -ruler.enable-api
     	Enable the ruler config API. (default true)
   -ruler.evaluation-delay-duration duration

docs/sources/operators-guide/configure/about-dns-service-discovery.md

@@ -35,4 +35,6 @@ You select a discovery mode by adding one of the following supported prefixes to
 - **`dnssrvnoa+`**<br />
   The domain name after the prefix is looked up as a SRV query, with no A/AAAA lookup made after that. For example: `dnssrvnoa+_memcached._tcp.memcached.namespace.svc.cluster.local`.
 
+The Alertmanager URL must contain also the scheme. For example: `dns+http://alermanager.local:8080`.
+
 If no prefix is provided, the provided IP or hostname is used without pre-resolving it.

docs/sources/operators-guide/configure/reference-configuration-parameters/index.md

@@ -1243,8 +1243,8 @@ The `ruler` block configures the ruler.
 
 # Comma-separated list of URL(s) of the Alertmanager(s) to send notifications
 # to. Each URL is treated as a separate group. Multiple Alertmanagers in HA per
-# group can be supported by using DNS service discovery format. Basic auth is
-# supported as part of the URL.
+# group can be supported by using DNS service discovery format, comprehensive of
+# the scheme. Basic auth is supported as part of the URL.
 # CLI flag: -ruler.alertmanager-url
 [alertmanager_url: <string> | default = ""]
 

pkg/ruler/ruler.go

@@ -141,7 +141,7 @@ func (cfg *Config) RegisterFlags(f *flag.FlagSet, logger log.Logger) {
 	f.DurationVar(&cfg.EvaluationInterval, "ruler.evaluation-interval", 1*time.Minute, "How frequently to evaluate rules")
 	f.DurationVar(&cfg.PollInterval, "ruler.poll-interval", 1*time.Minute, "How frequently to poll for rule changes")
 
-	f.StringVar(&cfg.AlertmanagerURL, "ruler.alertmanager-url", "", "Comma-separated list of URL(s) of the Alertmanager(s) to send notifications to. Each URL is treated as a separate group. Multiple Alertmanagers in HA per group can be supported by using DNS service discovery format. Basic auth is supported as part of the URL.")
+	f.StringVar(&cfg.AlertmanagerURL, "ruler.alertmanager-url", "", "Comma-separated list of URL(s) of the Alertmanager(s) to send notifications to. Each URL is treated as a separate group. Multiple Alertmanagers in HA per group can be supported by using DNS service discovery format, comprehensive of the scheme. Basic auth is supported as part of the URL.")
 	f.DurationVar(&cfg.AlertmanagerRefreshInterval, "ruler.alertmanager-refresh-interval", 1*time.Minute, "How long to wait between refreshing DNS resolutions of Alertmanager hosts.")
 	f.IntVar(&cfg.NotificationQueueCapacity, "ruler.notification-queue-capacity", 10000, "Capacity of the queue for notifications to be sent to the Alertmanager.")
 	f.DurationVar(&cfg.NotificationTimeout, "ruler.notification-timeout", 10*time.Second, "HTTP timeout duration when sending notifications to the Alertmanager.")