[loki-canary] Support passing loki address as environment variable (#8205)

cmd/loki-canary/main.go

@@ -95,7 +95,11 @@ func main() {
 	}
 
 	if *addr == "" {
-		_, _ = fmt.Fprintf(os.Stderr, "Must specify a Loki address with -addr\n")
+		*addr = os.Getenv("LOKI_ADDRESS")
+	}
+
+	if *addr == "" {
+		_, _ = fmt.Fprintf(os.Stderr, "Must specify a Loki address with -addr or set the environemnt variable LOKI_ADDRESS\n")
 		os.Exit(1)
 	}
 

docs/sources/operations/loki-canary/_index.md

@@ -272,9 +272,10 @@ $ make loki-canary-image
 
 ## Configuration
 
-The address of Loki must be passed in with the `-addr` flag, and if your Loki
+The address of Loki must be passed in with the `-addr` flag or by setting the
-server uses TLS, `-tls=true` must also be provided. Note that using TLS will
+environment variable `LOKI_ADDRESS`, and if your Loki server uses TLS, `-tls=true`
-cause the WebSocket connection to use `wss://` instead of `ws://`.
+must also be provided. Note that using TLS will cause the WebSocket connection
+to use `wss://` instead of `ws://`.
 
 The `-labelname` and `-labelvalue` flags should also be provided, as these are
 used by Loki Canary to filter the log stream to only process logs for the
@@ -302,7 +303,7 @@ All options:
 
 ```
   -addr string
-    	The Loki server URL:Port, e.g. loki:3100
+    	The Loki server URL:Port, e.g. loki:3100. Loki address can also be set using the environment variable LOKI_ADDRESS.
   -buckets int
     	Number of buckets in the response_latency histogram (default 10)
   -ca-file string