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This repository contains two nuget packages: Serilog.Sinks.Elasticsearch and Serilog.Formatting.Elasticsearch.

Table of contents

What is this sink

The Serilog Elasticsearch sink project is a sink (basically a writer) for the Serilog logging framework. Structured log events are written to sinks and each sink is responsible for writing it to its own backend, database, store etc. This sink delivers the data to Elasticsearch, a NoSQL search engine. It does this in a similar structure as Logstash and makes it easy to use Kibana for visualizing your logs.

Features

Quick start

Elasticsearch sinks

Install-Package serilog.sinks.elasticsearch

Simplest way to register this sink is to use default configuration:

var loggerConfig = new LoggerConfiguration()
    .WriteTo.Elasticsearch(new ElasticsearchSinkOptions(new Uri("http://localhost:9200")));

Or, if using .NET Core and Serilog.Settings.Configuration Nuget package and appsettings.json, default configuration would look like this:

{
  "Serilog": {
    "Using": [ "Serilog.Sinks.Elasticsearch" ],
    "MinimumLevel": "Warning",
    "WriteTo": [
      {
        "Name": "Elasticsearch",
        "Args": {
          "nodeUris": "http://localhost:9200"
        }
      }
    ],
    "Enrich": [ "FromLogContext", "WithMachineName" ],
    "Properties": {
      "Application": "ImmoValuation.Swv - Web"
    }
  }
}

More elaborate configuration, using additional Nuget packages (e.g. Serilog.Enrichers.Environment) would look like:

{
  "Serilog": {
    "Using": [ "Serilog.Sinks.Elasticsearch" ],
    "MinimumLevel": "Warning",
    "WriteTo": [
      {
        "Name": "Elasticsearch",
        "Args": {
          "nodeUris": "http://localhost:9200"
        }
      }
    ],
    "Enrich": [ "FromLogContext", "WithMachineName" ],
    "Properties": {
      "Application": "My app"
    }
  }
}

This way the sink will detect version of Elasticsearch server (DetectElasticsearchVersion is set to true by default) and handle TypeName behavior correctly, based on the server version (6.x, 7.x or 8.x).

Disable detection of Elasticsearch server version

Alternatively, DetectElasticsearchVersion can be set to false and certain option can be configured manually. In that case, the sink will assume version 7 of Elasticsearch, but options will be ignored due to a potential version incompatibility.

For example, you can configure the sink to force registeration of v6 index template. Be aware that the AutoRegisterTemplate option will not overwrite an existing template.

var loggerConfig = new LoggerConfiguration()
    .WriteTo.Elasticsearch(new ElasticsearchSinkOptions(new Uri("http://localhost:9200") ){
             DetectElasticsearchVersion = false,
             AutoRegisterTemplate = true,
             AutoRegisterTemplateVersion = AutoRegisterTemplateVersion.ESv6
     });

Configurable properties

Besides a registration of the sink in the code, it is possible to register it using appSettings reader (from v2.0.42+) reader (from v2.0.42+) as shown below.

This example shows the options that are currently available when using the appSettings reader.

  <appSettings>
    <add key="serilog:using" value="Serilog.Sinks.Elasticsearch"/>
    <add key="serilog:write-to:Elasticsearch.nodeUris" value="http://localhost:9200;http://remotehost:9200"/>
    <add key="serilog:write-to:Elasticsearch.indexFormat" value="custom-index-{0:yyyy.MM}"/>
    <add key="serilog:write-to:Elasticsearch.templateName" value="myCustomTemplate"/>
    <add key="serilog:write-to:Elasticsearch.typeName" value="myCustomLogEventType"/>
    <add key="serilog:write-to:Elasticsearch.pipelineName" value="myCustomPipelineName"/>
    <add key="serilog:write-to:Elasticsearch.batchPostingLimit" value="50"/>
    <add key="serilog:write-to:Elasticsearch.batchAction" value="Create"/><!-- "Index" is default -->
    <add key="serilog:write-to:Elasticsearch.period" value="2"/>
    <add key="serilog:write-to:Elasticsearch.inlineFields" value="true"/>
    <add key="serilog:write-to:Elasticsearch.restrictedToMinimumLevel" value="Warning"/>
    <add key="serilog:write-to:Elasticsearch.bufferBaseFilename" value="C:\Temp\SerilogElasticBuffer"/>
    <add key="serilog:write-to:Elasticsearch.bufferFileSizeLimitBytes" value="5242880"/>
    <add key="serilog:write-to:Elasticsearch.bufferLogShippingInterval" value="5000"/>
    <add key="serilog:write-to:Elasticsearch.bufferRetainedInvalidPayloadsLimitBytes" value="5000"/>
    <add key="serilog:write-to:Elasticsearch.bufferFileCountLimit " value="31"/>
    <add key="serilog:write-to:Elasticsearch.connectionGlobalHeaders" value="Authorization=Bearer SOME-TOKEN;OtherHeader=OTHER-HEADER-VALUE" />
    <add key="serilog:write-to:Elasticsearch.connectionTimeout" value="5" />
    <add key="serilog:write-to:Elasticsearch.emitEventFailure" value="WriteToSelfLog" />
    <add key="serilog:write-to:Elasticsearch.queueSizeLimit" value="100000" />
    <add key="serilog:write-to:Elasticsearch.autoRegisterTemplate" value="true" />
    <add key="serilog:write-to:Elasticsearch.autoRegisterTemplateVersion" value="ESv7" />
    <add key="serilog:write-to:Elasticsearch.detectElasticsearchVersion" value="false" /><!-- `true` is default -->
    <add key="serilog:write-to:Elasticsearch.overwriteTemplate" value="false" />
    <add key="serilog:write-to:Elasticsearch.registerTemplateFailure" value="IndexAnyway" />
    <add key="serilog:write-to:Elasticsearch.deadLetterIndexName" value="deadletter-{0:yyyy.MM}" />
    <add key="serilog:write-to:Elasticsearch.numberOfShards" value="20" />
    <add key="serilog:write-to:Elasticsearch.numberOfReplicas" value="10" />
    <add key="serilog:write-to:Elasticsearch.formatProvider" value="My.Namespace.MyFormatProvider, My.Assembly.Name" />
    <add key="serilog:write-to:Elasticsearch.connection" value="My.Namespace.MyConnection, My.Assembly.Name" />
    <add key="serilog:write-to:Elasticsearch.serializer" value="My.Namespace.MySerializer, My.Assembly.Name" />
    <add key="serilog:write-to:Elasticsearch.connectionPool" value="My.Namespace.MyConnectionPool, My.Assembly.Name" />
    <add key="serilog:write-to:Elasticsearch.customFormatter" value="My.Namespace.MyCustomFormatter, My.Assembly.Name" />
    <add key="serilog:write-to:Elasticsearch.customDurableFormatter" value="My.Namespace.MyCustomDurableFormatter, My.Assembly.Name" />
    <add key="serilog:write-to:Elasticsearch.failureSink" value="My.Namespace.MyFailureSink, My.Assembly.Name" />
  </appSettings>

With the appSettings configuration the nodeUris property is required. Multiple nodes can be specified using , or ; to separate them. All other properties are optional. Also required is the <add key="serilog:using" value="Serilog.Sinks.Elasticsearch"/> setting to include this sink. All other properties are optional. If you do not explicitly specify an indexFormat-setting, a generic index such as 'logstash-[current_date]' will be used automatically.

And start writing your events using Serilog.

Elasticsearch formatters

Install-Package serilog.formatting.elasticsearch

The Serilog.Formatting.Elasticsearch nuget package consists of a several formatters:

Override default formatter if it's possible with selected sink

var loggerConfig = new LoggerConfiguration()
  .WriteTo.Console(new ElasticsearchJsonFormatter());

More information

A note about fields inside Elasticsearch

Be aware that there is an explicit and implicit mapping of types inside an Elasticsearch index. A value called X as a string will be indexed as being a string. Sending the same X as an integer in a next log message will not work. ES will raise a mapping exception, however it is not that evident that your log item was not stored due to the bulk actions performed.

So be careful about defining and using your fields (and type of fields). It is easy to miss that you first send a {User} as a simple username (string) and next as a User object. The first mapping dynamically created in the index wins. See also issue #184 for details and a possible solution. There are also limits in ES on the number of dynamic fields you can actually throw inside an index.

A note about Kibana

In order to avoid a potentially deeply nested JSON structure for exceptions with inner exceptions, by default the logged exception and it's inner exception is logged as an array of exceptions in the field exceptions. Use the 'Depth' field to traverse the inner exceptions flow.

However, not all features in Kibana work just as well with JSON arrays - for instance, including exception fields on dashboards and visualizations. Therefore, we provide an alternative formatter, ExceptionAsObjectJsonFormatter, which will serialize the exception into the exception field as an object with nested InnerException properties. This was also the default behavior of the sink before version 2.

To use it, simply specify it as the CustomFormatter when creating the sink:

    new ElasticsearchSink(new ElasticsearchSinkOptions(url)
    {
      CustomFormatter = new ExceptionAsObjectJsonFormatter(renderMessage:true)
    });

JSON appsettings.json configuration

To use the Elasticsearch sink with Microsoft.Extensions.Configuration, for example with ASP.NET Core or .NET Core, use the Serilog.Settings.Configuration package. First install that package if you have not already done so:

Install-Package Serilog.Settings.Configuration

Instead of configuring the sink directly in code, call ReadFrom.Configuration():

var configuration = new ConfigurationBuilder()
    .SetBasePath(env.ContentRootPath)
    .AddJsonFile("appsettings.json")
    .Build();

var logger = new LoggerConfiguration()
    .ReadFrom.Configuration(configuration)
    .CreateLogger();

In your appsettings.json file, under the Serilog node, :

{
  "Serilog": {
    "WriteTo": [{
        "Name": "Elasticsearch",
        "Args": {
          "nodeUris": "http://localhost:9200;http://remotehost:9200/",
          "indexFormat": "custom-index-{0:yyyy.MM}",
          "templateName": "myCustomTemplate",
          "typeName": "myCustomLogEventType",
          "pipelineName": "myCustomPipelineName",
          "batchPostingLimit": 50,
          "batchAction": "Create",
          "period": 2,
          "inlineFields": true,
          "restrictedToMinimumLevel": "Warning",
          "bufferBaseFilename":  "C:/Temp/docker-elk-serilog-web-buffer",
          "bufferFileSizeLimitBytes": 5242880,
          "bufferLogShippingInterval": 5000,
          "bufferRetainedInvalidPayloadsLimitBytes": 5000,
          "bufferFileCountLimit": 31,
          "connectionGlobalHeaders" :"Authorization=Bearer SOME-TOKEN;OtherHeader=OTHER-HEADER-VALUE",
          "connectionTimeout": 5,
          "emitEventFailure": "WriteToSelfLog",
          "queueSizeLimit": "100000",
          "autoRegisterTemplate": true,
          "autoRegisterTemplateVersion": "ESv2",
          "overwriteTemplate": false,
          "registerTemplateFailure": "IndexAnyway",
          "deadLetterIndexName": "deadletter-{0:yyyy.MM}",
          "numberOfShards": 20,
          "numberOfReplicas": 10,
          "templateCustomSettings": [{ "index.mapping.total_fields.limit": "10000000" } ],
          "formatProvider": "My.Namespace.MyFormatProvider, My.Assembly.Name",
          "connection": "My.Namespace.MyConnection, My.Assembly.Name",
          "serializer": "My.Namespace.MySerializer, My.Assembly.Name",
          "connectionPool": "My.Namespace.MyConnectionPool, My.Assembly.Name",
          "customFormatter": "My.Namespace.MyCustomFormatter, My.Assembly.Name",
          "customDurableFormatter": "My.Namespace.MyCustomDurableFormatter, My.Assembly.Name",
          "failureSink": "My.Namespace.MyFailureSink, My.Assembly.Name"
        }
    }]
  }
}

See the XML <appSettings> example above for a discussion of available Args options.

Handling errors

From version 5.5 you have the option to specify how to handle issues with Elasticsearch. Since the sink delivers in a batch, it might be possible that one or more events could actually not be stored in the Elasticsearch store. Can be a mapping issue for example. It is hard to find out what happened here. There is a new option called EmitEventFailure which is an enum (flagged) with the following options:

An example:

.WriteTo.Elasticsearch(new ElasticsearchSinkOptions(new Uri("http://localhost:9200"))
                {
                    FailureCallback = e => Console.WriteLine("Unable to submit event " + e.MessageTemplate),
                    EmitEventFailure = EmitEventFailureHandling.WriteToSelfLog |
                                       EmitEventFailureHandling.WriteToFailureSink |
                                       EmitEventFailureHandling.RaiseCallback,
                    FailureSink = new FileSink("./failures.txt", new JsonFormatter(), null)
                })

With the AutoRegisterTemplate option the sink will write a default template to Elasticsearch. When this template is not there, you might not want to index as it can influence the data quality. Since version 5.5 you can use the RegisterTemplateFailure option. Set it to one of the following options:

Since version 7 you can specify an action to do when log row was denied by the elasticsearch because of the data (payload) if durable file is specied. i.e.

BufferCleanPayload = (failingEvent, statuscode, exception) =>
                    {
                        dynamic e = JObject.Parse(failingEvent);
                        return JsonConvert.SerializeObject(new Dictionary<string, object>()
                        {
                            { "@timestamp",e["@timestamp"]},
                            { "level","Error"},
                            { "message","Error: "+e.message},
                            { "messageTemplate",e.messageTemplate},
                            { "failingStatusCode", statuscode},
                            { "failingException", exception}
                        });
                    },

The IndexDecider didnt worked well when durable file was specified so an option to specify BufferIndexDecider is added. Datatype of logEvent is string i.e.

 BufferIndexDecider = (logEvent, offset) => "log-serilog-" + (new Random().Next(0, 2)),

Option BufferFileCountLimit is added. The maximum number of log files that will be retained. including the current log file. For unlimited retention, pass null. The default is 31. Option BufferFileSizeLimitBytes is added The maximum size, in bytes, to which the buffer log file for a specific date will be allowed to grow. By default 100L * 1024 * 1024 will be applied.

Breaking changes

Version 9

Version 7

Version 6

Starting from version 6, the sink has been upgraded to work with Elasticsearch 6.0 and has support for the new templates used by ES 6.

If you use the AutoRegisterTemplate option, you need to set the AutoRegisterTemplateVersion option to ESv6 in order to generate default templates that are compatible with the breaking changes in ES 6.

Version 4

Starting from version 4, the sink has been upgraded to work with Serilog 2.0 and has .NET Core support.

Version 3

Starting from version 3, the sink supports the Elasticsearch.Net 2 package and Elasticsearch version 2. If you need Elasticsearch 1.x support, then stick with version 2 of the sink. The function

protected virtual ElasticsearchResponse<T> EmitBatchChecked<T>(IEnumerable<LogEvent> events)

now uses a generic type. This allows you to map to either DynamicResponse when using Elasticsearch.NET or to BulkResponse if you want to use NEST.

We also dropped support for .NET 4 since the Elasticsearch.NET client also does not support this version of the framework anymore. If you need to use .net 4, then you need to stick with the 2.x version of the sink.

Version 2

Be aware that version 2 introduces some breaking changes.