[SelfDiagnosticsModule] Add user guide for troubleshooting (#1477)

* Add troubleshooting doc to enable self diagnostics module

* Add explanation on EventLevel and parsing failure behavior.

* Change the configuration file name to OTEL_DIAGNOSTICS.json

* Add more explanation

* Rename EventLevel to LogLevel

* Add link to EventLevel enum

Co-authored-by: Cijo Thomas <[email protected]>

src/OpenTelemetry/Internal/SelfDiagnosticsConfigParser.cs

@@ -24,7 +24,7 @@ namespace OpenTelemetry.Internal
 {
     internal class SelfDiagnosticsConfigParser
     {
-        private const string ConfigFileName = "DiagnosticsConfiguration.json";
+        private const string ConfigFileName = "OTEL_DIAGNOSTICS.json";
         private const int FileSizeLowerLimit = 1024;  // Lower limit for log file size in KB: 1MB
         private const int FileSizeUpperLimit = 128 * 1024;  // Upper limit for log file size in KB: 128MB
 
@@ -39,19 +39,19 @@ internal class SelfDiagnosticsConfigParser
         private static readonly Regex FileSizeRegex = new Regex(
             @"""FileSize""\s*:\s*(?<FileSize>\d+)", RegexOptions.IgnoreCase | RegexOptions.Compiled);
 
-        private static readonly Regex EventLevelRegex = new Regex(
-            @"""EventLevel""\s*:\s*""(?<EventLevel>.*?)""", RegexOptions.IgnoreCase | RegexOptions.Compiled);
+        private static readonly Regex LogLevelRegex = new Regex(
+            @"""LogLevel""\s*:\s*""(?<LogLevel>.*?)""", RegexOptions.IgnoreCase | RegexOptions.Compiled);
 
         // This class is called in SelfDiagnosticsConfigRefresher.UpdateMemoryMappedFileFromConfiguration
         // in both main thread and the worker thread.
         // In theory the variable won't be access at the same time because worker thread first Task.Delay for a few seconds.
         private byte[] configBuffer;
 
-        public bool TryGetConfiguration(out string logDirectory, out int fileSizeInKB, out EventLevel eventLevel)
+        public bool TryGetConfiguration(out string logDirectory, out int fileSizeInKB, out EventLevel logLevel)
         {
             logDirectory = null;
             fileSizeInKB = 0;
-            eventLevel = EventLevel.LogAlways;
+            logLevel = EventLevel.LogAlways;
             try
             {
                 using FileStream file = File.Open(ConfigFileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite | FileShare.Delete);
@@ -84,12 +84,12 @@ public bool TryGetConfiguration(out string logDirectory, out int fileSizeInKB, o
                     fileSizeInKB = FileSizeUpperLimit;
                 }
 
-                if (!TryParseEventLevel(configJson, out var eventLevelString))
+                if (!TryParseLogLevel(configJson, out var logLevelString))
                 {
                     return false;
                 }
 
-                eventLevel = (EventLevel)Enum.Parse(typeof(EventLevel), eventLevelString);
+                logLevel = (EventLevel)Enum.Parse(typeof(EventLevel), logLevelString);
                 return true;
             }
             catch (Exception)
@@ -114,11 +114,11 @@ internal static bool TryParseFileSize(string configJson, out int fileSizeInKB)
             return fileSizeResult.Success && int.TryParse(fileSizeResult.Groups["FileSize"].Value, out fileSizeInKB);
         }
 
-        internal static bool TryParseEventLevel(string configJson, out string eventLevel)
+        internal static bool TryParseLogLevel(string configJson, out string logLevel)
         {
-            var eventLevelResult = EventLevelRegex.Match(configJson);
-            eventLevel = eventLevelResult.Groups["EventLevel"].Value;
-            return eventLevelResult.Success && !string.IsNullOrWhiteSpace(eventLevel);
+            var logLevelResult = LogLevelRegex.Match(configJson);
+            logLevel = logLevelResult.Groups["LogLevel"].Value;
+            return logLevelResult.Success && !string.IsNullOrWhiteSpace(logLevel);
         }
     }
 }

src/OpenTelemetry/README.md

@@ -84,6 +84,54 @@ using var otel = Sdk.CreateTracerProvider(b => b
   * [Building your own Processor](../../docs/trace/extending-the-sdk/README.md#processor)
   * [Building your own Sampler](../../docs/trace/extending-the-sdk/README.md#sampler)
 
+### Troubleshooting
+
+Self diagnostics module is provided to help troubleshooting. When enabled,
+internal events generated by OpenTelemetry will be written to a log file.
+These events contain important debugging information and error messages.
+
+To enable self diagnostics, go to the current directory of your process and
+create a configuration file named `OTEL_DIAGNOSTICS.json` with the following
+content:
+
+```json
+{
+    "LogDirectory": ".",
+    "FileSize": 1024,
+    "LogLevel": "Error"
+}
+```
+
+`LogDirectory` is the directory of the output file. It can be an absolute path
+or a relative path to the current directory. `FileSize` is a positive integer,
+which specifies the log file size in
+[KiB](https://en.wikipedia.org/wiki/Kibibyte).
+`LogLevel` is the lowest level of the events to be captured.
+It has to be one of the
+[values](https://docs.microsoft.com/dotnet/api/system.diagnostics.tracing.eventlevel#fields)
+of the [`EventLevel`
+enum](https://docs.microsoft.com/dotnet/api/system.diagnostics.tracing.eventlevel).
+(The level signifies the severity of an event. Lower severity levels encompass
+higher severity levels. For example, `Warning` includes the `Error` and
+`Critical` levels, which are higher in severity. See
+[here](https://docs.microsoft.com/dotnet/api/system.diagnostics.tracing.eventlevel)
+for more.)
+
+The SDK will attempt to open the configuration file in non-exclusive read-only
+mode, read the file and parse it as the configuration file every 3 seconds. If
+the SDK fails to parse the `LogDirectory`, `FileSize` or `LogLevel` fields as
+the specified format, the configuration file will be treated as invalid and no
+log file would be generated. Otherwise, it will create or overwrite a
+`FileSize`-KiB file at the specific directory `LogDirectory` with the log file
+named as `ExecutableName.ProcessId.log` (e.g. `foobar.exe.12345.log`).
+
+Note that the `FileSize` has to be between 1 MiB and 128 MiB (inclusive), or it
+will be rounded to the closest upper or lower limit.  When the `LogDirectory` or
+`FileSize` is found to be changed, the SDK will create or overwrite a file with
+new logs according to the new configuration.  The configuration file has to be
+no more than 4 KiB. In case the file is larger than 4 KiB, only the first 4 KiB
+of content will be read.
+
 ## References
 
 * [OpenTelemetry Project](https://opentelemetry.io/)

test/OpenTelemetry.Tests/Internal/SelfDiagnosticsConfigParserTest.cs

@@ -81,15 +81,15 @@ public void SelfDiagnosticsConfigParser_TryParseFileSize_MissingField()
 
         [Fact]
         [Trait("Platform", "Any")]
-        public void SelfDiagnosticsConfigParser_TryParseEventLevel()
+        public void SelfDiagnosticsConfigParser_TryParseLogLevel()
         {
             string configJson = @"{
                     ""LogDirectory"": ""Diagnostics"",
                     ""FileSize"": 1024,
-                    ""EventLevel"": ""Error""
+                    ""LogLevel"": ""Error""
                     }";
-            Assert.True(SelfDiagnosticsConfigParser.TryParseEventLevel(configJson, out string eventLevelString));
-            Assert.Equal("Error", eventLevelString);
+            Assert.True(SelfDiagnosticsConfigParser.TryParseLogLevel(configJson, out string logLevelString));
+            Assert.Equal("Error", logLevelString);
         }
     }
 }