Protected the automated adding of event properties as Loki labels beh…

…ind a feature flag eventPropertiesAsLabels and documented it. Warned users when using the feature flag.

README.md

@@ -45,6 +45,7 @@ Under .NET Core, [remember to register](https://github.com/nlog/nlog/wiki/Regist
       orderWrites="true"
       compressionLevel="noCompression"
       layout="${level}|${message}${onexception:|${exception:format=type,message,method:maxInnerExceptionLevel=5:innerFormat=shortType,message,method}}|source=${logger}"
+      eventPropertiesAsLabels="false"
       sendLastFormatParameter="false"
       proxyUrl="http://proxy:8888"
       proxyUser="username"
@@ -96,7 +97,9 @@ Under .NET Core, [remember to register](https://github.com/nlog/nlog/wiki/Regist
 `layout` - While it is possible to define a simple layout structure in the attributes of the target configuration,
   prefer using a JsonLayout to structure your logs. This will allow better parsing in Grafana Loki.
 
-`sendLastFormatParameter`: enables the last parameter of a log message format to be sent to Loki as separate fields per property. Example:
+`eventPropertiesAsLabels`: creates one Grafana Loki's label per event property. Beware, this goes against [Grafana Loki's best practices](https://grafana.com/docs/loki/latest/best-practices/) since _Too many label value combinations leads to too many streams._ In order to structure your logs, you are advised to keep away from this feature and to use the `JsonLayout` provided in the example.
+
+`sendLastFormatParameter`: enables the last parameter of a log message format to be sent to Grafana Loki as separate fields per property. Feature `eventPropertiesAsLabels` must be `true` as well. Example:
 
 ```csharp
 // using simple anonymous type object to create custom fields for a log entry
@@ -163,22 +166,6 @@ These raw messages would look like the following in Grafana Loki :
 See [Log Queries and Parser Expressions in Loki](https://grafana.com/docs/loki/latest/logql/log_queries/#parser-expression)
 for more details.
 
-### Additional Properties
-
-Like Gelf target, NLog.Loki reads custom fields from the log event properties. It significantly streamlines the migration process from Graylog to Loki. Example:
-
-```csharp
-// using additional properties to create custom fields for a log entry
-var eventInfo = new LogEventInfo
-{
-    Message = "Testing additional properties inside LogEventInfo",
-    Level = LogLevel.Info,
-};
-eventInfo.Properties.Add("publisher", "ACME Publisher");
-eventInfo.Properties.Add("releaseDate", DateTime.Now);
-log.Log(eventInfo);
-```
-
 ### Benchmark
 
 See [NLog.Loki.Benchmarks](https://github.com/corentinaltepe/nlog.loki.benchmark) for benchmark between HTTP and gRPC clients for NLog targets for Grafana Loki.

src/NLog.Loki/LokiTarget.cs

@@ -28,6 +28,7 @@ public class LokiTarget : AsyncTaskTarget
     public Layout Password { get; set; }
 
     public bool SendLastFormatParameter { get; set; }
+    public bool EventPropertiesAsLabels { get; set; }
 
     /// <summary>
     /// Orders the logs by timestamp before sending them to Loki. False by default.
@@ -82,14 +83,15 @@ private IEnumerable<LokiEvent> GetLokiEvents(IEnumerable<LogEventInfo> logEvents
 
     private LokiEvent GetLokiEvent(LogEventInfo logEvent)
     {
-        var labels = new LokiLabels(RenderAndMapLokiLabels(Labels, logEvent, SendLastFormatParameter));
+        var labels = new LokiLabels(RenderAndMapLokiLabels(Labels, logEvent, SendLastFormatParameter, EventPropertiesAsLabels));
         return new LokiEvent(labels, logEvent.TimeStamp, RenderLogEvent(Layout, logEvent));
     }
 
     private static ISet<LokiLabel> RenderAndMapLokiLabels(
     IList<LokiTargetLabel> lokiTargetLabels,
     LogEventInfo logEvent,
-    bool sendLastFormatParameter)
+    bool sendLastFormatParameter,
+    bool eventPropertiesAsLabels)
     {
         var set = new HashSet<LokiLabel>();
         for(var i = 0; i < lokiTargetLabels.Count; i++)
@@ -108,11 +110,13 @@ private static ISet<LokiLabel> RenderAndMapLokiLabels(
             }
         }
 
-        // programmer might also want to create fields in loki using event properties
-        foreach(var property in logEvent.Properties)
-        {
-            _ = set.Add(new LokiLabel(property.Key.ToString(), property.Value?.ToString() ?? ""));
-        }
+        // programmer might also want to create labels in loki using event properties
+        // This goes against Loki best pratices as it tends to create too many streams.
+        // But the feature was requested twice in a short span so it is included in the library,
+        // with warnings in the readme.
+        if(eventPropertiesAsLabels)
+            foreach(var property in logEvent.Properties)
+                _ = set.Add(new LokiLabel(property.Key.ToString(), property.Value?.ToString() ?? ""));
 
         return set;
     }

src/Template/nlog.config

@@ -18,7 +18,8 @@
       retryCount="3"
       orderWrites="true"
       compressionLevel="fastest"
-      sendLastFormatParameter="true">
+      eventPropertiesAsLabels="false"
+      sendLastFormatParameter="false">
       <label name="app" layout="template" />
       <layout xsi:type="JsonLayout" includeEventProperties="true">
         <attribute name="level" layout="${level} "/>