NLog Loki gRPC Target

This is an NLog target that sends messages to Loki using Loki's with a gRPC client. For HTTP client, use this target instead.

Loki is a horizontally-scalable, highly-available, multi-tenant log aggregation system inspired by Prometheus. It is designed to be very cost effective and easy to operate.

Installation

The NLog.Targets.Loki.gRPC NuGet package can be found here. You can install it via one of the following commands below:

NuGet command:

Install-Package NLog.Targets.Loki.gRPC

.NET Core CLI command:

dotnet add package NLog.Targets.Loki.gRPC

Usage

Under .NET Core, remember to register NLog.Loki.Grpc as an extension assembly with NLog. You can now add a Loki target to your configuration file:

<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  
  <extensions>
    <add assembly="NLog.Loki.Grpc" />
  </extensions>

  <!-- Loki target is async, so there is no need to wrap it in an async target wrapper. -->
  <targets>
    <target 
      name="loki" 
      xsi:type="loki.grpc"
      batchSize="200"
      taskDelayMilliseconds="500"
      endpoint="http://localhost:3100"
      orderWrites="true"
      layout="${level}|${message}${onexception:|${exception:format=type,message,method:maxInnerExceptionLevel=5:innerFormat=shortType,message,method}}|source=${logger}">
      <!-- Loki requires at least one label associated with the log stream. 
      Make sure you specify at least one label here. -->
      <label name="app" layout="my-app-name" />
      <label name="server" layout="${hostname:lowercase=true}" />
    </target>
  </targets>

  <rules>
    <logger name="*" minlevel="Info" writeTo="loki" />
  </rules>

</nlog>

endpoint must resolve to a fully-qualified absolute URL of the Loki Server when running in a Single Proccess Mode or of the Loki Distributor when running in Microservices Mode.

orderWrites - Orders the logs by timestamp before sending them to loki when logs are batched in a single HTTP call. This is required if you use Loki v2.3 or below. But it is not required if you use Loki v2.4 or above (see out-of-order writes). You are strongly advised to set this value to false when using Loki v2.4+ since it reduces allocations by about 20% by the serializer (default true).

label elements can be used to enrich messages with additional labels. label/@layout support usual NLog layout renderers.

Async Target

NLog.Loki.gRPC is an async target. You should not wrap it in an AsyncWrapper target. The following configuration options are supported. Make sure to adjust them to the expected throughput and criticality of your application's logs, especially the batch size, retry count and task delay.

taskTimeoutSeconds - How many seconds a Task is allowed to run before it is cancelled (default 150 secs).

retryDelayMilliseconds - How many milliseconds to wait before next retry (default 500ms, and will be doubled on each retry).

retryCount - How many attempts to retry the same Task, before it is aborted (default 0, meaning no retry).

batchSize - Gets or sets the number of log events that should be processed in a batch by the lazy writer thread (default 1).

taskDelayMilliseconds - How many milliseconds to delay the actual write operation to optimize for batching (default 1 ms).

queueLimit - Gets or sets the limit on the number of requests in the lazy writer thread request queue (default 10000).

overflowAction - Gets or sets the action to be taken when the lazy writer thread request queue count exceeds the set limit (default Discard).

Benchmark

See NLog.Loki.Benchmarks for benchmark between HTTP and gRPC clients for NLog targets for Loki.