Logging and monitoring

Logging with ILogger

As an alternative to TraceWriter, an instance of ILogger can be used instead.

The advantage of using ILogger instead of TraceWriter is that you get support for structured logging, which allows for richer analytics support. This is helpful if you target your logs at a tool like Application Insights.

C#

[FunctionName("ILoggerHttpLogging")]
public static HttpResponseMessage Run([HttpTrigger(AuthorizationLevel.Anonymous, "GET")]HttpRequestMessage req, ILogger log)
{
    log.LogInformation("101 Azure Function Demo - Logging with ITraceWriter");
    log.LogTrace("Here is a verbose log message");
    log.LogWarning("Here is a warning log message");
    log.LogError("Here is an error log message");
    log.LogCritical("This is a critical log message => {message}", "We have a big problem");
    return req.CreateResponse(HttpStatusCode.OK);
}

F#

[<FunctionName("ILoggerHttpLogging")>]
let Run([<HttpTrigger(AuthorizationLevel.Anonymous, "GET")>] req: HttpRequestMessage, log: ILogger) =
  log.LogInformation "101 Azure Function Demo - Logging with ITraceWriter"
  log.LogTrace "Here is a verbose log message"
  log.LogWarning "Here is a warning log message"
  log.LogError "Here is an error log message"
  log.LogCritical("This is a critical log message => {message}", "We have a big problem")
  req.CreateResponse HttpStatusCode.OK

Takeaways

• ILogger can be used as an alternative to TraceWriter
• ILogger supports structured logging

Read more

• ILogger support
• ILogger extension methods

Basic logging with TraceWriter

To enable basic logging in your functions, you can include a parameter of type TraceWriter and an instance is provided to you. TraceWriter is defined in the Azure WebJobs SDK. The tracing property in host.json can be used to configure TraceWriter.

C#

[FunctionName("TraceWriterLogging")]
public static HttpResponseMessage Run([HttpTrigger(AuthorizationLevel.Anonymous, "GET")]HttpRequestMessage req, TraceWriter log)
{
    log.Info("101 Azure Function Demo - Basic logging with TraceWriter");
    log.Verbose("Here is a verbose log message");
    log.Warning("Here is a warning log message");
    log.Error("Here is an error log message");

    TraceEvent traceEvent = new TraceEvent(TraceLevel.Info, "and another one!");
    log.Trace(traceEvent);

    return req.CreateResponse(HttpStatusCode.OK);
}

F#

[<FunctionName("TraceWriterLogging")>]
let Run([<HttpTrigger(AuthorizationLevel.Anonymous, "GET")>] req: HttpRequestMessage, log: TraceWriter) =
  log.Info "101 Azure Function Demo - Basic logging with TraceWriter"
  log.Verbose "Here is a verbose log message"
  log.Warning "Here is a warning log message"
  log.Error "Here is an error log message"

  let traceEvent = TraceEvent(TraceLevel.Info, "and another one!")
  log.Trace traceEvent

  req.CreateResponse HttpStatusCode.OK

host.json

{
  "tracing": {
    "consoleLevel": "verbose"
  }
}

Takeaways

• You can optionally include a TraceWriter parameter to your function.
• TraceWriter provides the Trace, Verbose, Info, Warning & Error methods.
• TraceWriter is a part of the Microsoft.Azure.WebJobs package.
• Avoid using Console.WriteLine for logging.
• Log levels can be configured in host.json. The default log level is info.

Read more

• Azure Functions C# Developer Reference

Logging with a third-party logger

If you would rather use your preferred logger, you can easily do so by just adding a NuGet package.

The following code shows a function using the Serilog.Sinks.AzureTableStorage package.

C#

[FunctionName("ThirdPartyLogger")]
public static HttpResponseMessage Run([HttpTrigger(AuthorizationLevel.Anonymous, "GET")]HttpRequestMessage req)
{

    string connectionString = Environment.GetEnvironmentVariable("StorageAccountConnectionString", EnvironmentVariableTarget.Process);

    string tableName = Environment.GetEnvironmentVariable("StorageAccountTableName", EnvironmentVariableTarget.Process);

    Logger log = new LoggerConfiguration()
                .WriteTo.AzureTableStorage(connectionString, storageTableName: tableName, restrictedToMinimumLevel: LogEventLevel.Verbose)
                .CreateLogger();

    log.Debug("Here is a debug message {message}", "with some structured content");

    log.Verbose("Here is a verbose log message");
    log.Warning("Here is a warning log message");
    log.Error("Here is an error log message");

    return req.CreateResponse(HttpStatusCode.OK);
}

F#

[<FunctionName("ThirdPartyLogger")>]
let Run([<HttpTrigger(AuthorizationLevel.Anonymous, "GET")>] req: HttpRequestMessage) =
  let connectionString = Environment.GetEnvironmentVariable("StorageAccountConnectionString", EnvironmentVariableTarget.Process)

  let tableName = Environment.GetEnvironmentVariable("StorageAccountTableName", EnvironmentVariableTarget.Process)

  let log = LoggerConfiguration()
              .WriteTo
              .AzureTableStorage(connectionString, storageTableName = tableName, restrictedToMinimumLevel = LogEventLevel.Verbose)
              .CreateLogger()

  log.Debug("Here is a debug message {message}", "with some structured content")

  log.Verbose "Here is a verbose log message"
  log.Warning "Here is a warning log message"
  log.Error "Here is an error log message"

  req.CreateResponse HttpStatusCode.OK

Takeaways

• Alternative loggers can be used to capture log information from your functions.
• You can use NuGet to not only add loggers, but extend your functions with other functionality.

Read more

• Serilog
• Azure Functions C# Developer Reference