!! This document applies to the next version under development.

    See here for documentation on the latest released version.

Logback JSON encoder

Provides logback encoders, layouts, and appenders to log in JSON format.

Supports both regular LoggingEvents (logged through a Logger) and AccessEvents (logged via logback-access).

Originally written to support output in logstash's JSON format, but has evolved into a highly-configurable, general-purpose, JSON logging mechanism. The structure of the JSON output, and the data it contains, is fully configurable.

Contents:

• Including it in your project
• Usage
  • UDP Appender
  • TCP Appenders
    • SSL
  • Async Appenders
  • Encoders / Layouts
• LoggingEvent Fields
  • Standard Fields
  • MDC fields
  • Context fields
  • Caller Info Fields
  • Custom Fields
    • Global Custom Fields
    • Event-specific Custom Fields
• AccessEvent Fields
  • Standard Fields
  • Header Fields
• Customizing Standard Field Names
• Customizing TimeZone
• Customizing JSON Factory and Generator
• Customizing Logger Name Length
• Customizing Stack Traces
• Prefix/Suffix
• Composite Encoder/Layout
  • Providers for LoggingEvents
  • Providers for AccessEvents
  • Pattern JSON Provider
    • LoggingEvent patterns
    • AccessEvent patterns
• Debugging

## Including it in your project

Maven style:

<dependency>
  <groupId>net.logstash.logback</groupId>
  <artifactId>logstash-logback-encoder</artifactId>
  <version>4.2</version>
</dependency>

If you get ClassNotFoundException/NoClassDefFoundError/NoSuchMethodError at runtime, then ensure the required dependencies (and appropriate versions) as specified in the pom file from the maven repository exist on the runtime classpath. Specifically, the following need to be available on the runtime classpath:

• jackson-databind / jackson-core / jackson-annotations
• logback-core
• logback-classic (required for logging LoggingEvents)
• logback-access (required for logging AccessEvents)
• slf4j-api

Older versions than the ones specified in the pom file might work, but the versions in the pom file are what testing has been performed against.

## Usage

To log using JSON format, you must configure logback to use either:

• an appender provided by the logstash-logback-encoder library, OR
• an appender provided by logback (or another library) with an encoder or layout provided by the logstash-logback-encoder library

The appenders, encoders, and layouts provided by the logstash-logback-encoder library are as follows:

Format	Protocol	Function	LoggingEvent	AccessEvent
Logstash JSON	Syslog/UDP	Appender	LogstashSocketAppender	n/a
Logstash JSON	TCP	Appender	LogstashTcpSocketAppender	LogstashAccessTcpSocketAppender
any	any	Appender	LoggingEventAsyncDisruptorAppender	AccessEventAsyncDisruptorAppender
Logstash JSON	any	Encoder	LogstashEncoder	LogstashAccessEncoder
Logstash JSON	any	Layout	LogstashLayout	LogstashAccessLayout
General JSON	any	Encoder	LoggingEventCompositeJsonEncoder	AccessEventCompositeJsonEncoder
General JSON	any	Layout	LoggingEventCompositeJsonLayout	AccessEventCompositeJsonLayout

These encoders/layouts can generally be used by any logback appender (such as RollingFileAppender).

The general composite JSON encoders/layouts can be used to output any JSON format/data by configuring them with various JSON providers. The Logstash encoders/layouts are really just extensions of the general composite JSON encoders/layouts with a pre-defined set of providers.

The logstash encoders/layouts are easier to configure if you want to use the standard output format. Use the composite encoders/layouts if you want to heavily customize the output.

The *AsyncDisruptorAppender appenders are similar to logback's AsyncAppender, except that a LMAX Disruptor RingBuffer is used as the queuing mechanism, as opposed to a BlockingQueue. These async appenders can delegate to any other underlying logback appender.

### UDP Appender

To output JSON for LoggingEvents to a syslog/UDP channel, use the LogstashSocketAppender in your logback.xml like this:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <appender name="stash" class="net.logstash.logback.appender.LogstashSocketAppender">
    <host>MyAwesomeSyslogServer</host>
    <!-- port is optional (default value shown) -->
    <port>514</port>
  </appender>
  <root level="all">
    <appender-ref ref="stash" />
  </root>
</configuration>

Internally, the LogstashSocketAppender uses a LogstashLayout to perform the JSON formatting. Therefore, by default, the output will be logstash-compatible.

You can further customize the JSON output of LogstashSocketAppender just like you can with a LogstashLayout or LogstashEncoder as described in later sections. It is not necessary to configure a <layout> or <encoder> sub-element within the <appender> element in the logback configuration. All the properties of LogstashLayout or LogstashEncoder can be set at the <appender> level. For example, to configure global custom fields, you can specify

  <appender name="stash" class="net.logstash.logback.appender.LogstashSocketAppender">
    <host>MyAwesomeSyslogServer</host>
    <!-- port is optional (default value shown) -->
    <port>514</port>
    <customFields>{"appname":"myWebservice"}</customFields>
  </appender>

There currently is no way to log AccessEvents over syslog/UDP.

To receive syslog/UDP input in logstash, configure a syslog or udp input with the json codec in logstash's configuration like this:

input {
  syslog {
    codec => "json"
  }
}

### TCP Appenders

To output JSON for LoggingEvents over TCP, use a LogstashTcpSocketAppender with a LogstashEncoder or LoggingEventCompositeJsonEncoder.

Example logging appender configuration in logback.xml:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <appender name="stash" class="net.logstash.logback.appender.LogstashTcpSocketAppender">
      <!-- remoteHost and port are optional (default values shown) -->
      <remoteHost>127.0.0.1</remoteHost>
      <port>4560</port>
  
      <!-- encoder is required -->
      <encoder class="net.logstash.logback.encoder.LogstashEncoder" />
  </appender>
  
  <root level="DEBUG">
      <appender-ref ref="stash" />
  </root>
</configuration>

To output JSON for AccessEvents over TCP, use a LogstashAccessTcpSocketAppender with a LogstashAccessEncoder or AccessEventCompositeJsonEncoder.

Example access appender in logback-access.xml

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <appender name="stash" class="net.logstash.logback.appender.LogstashAccessTcpSocketAppender">
      <!-- remoteHost and port are optional (default values shown) -->
      <remoteHost>127.0.0.1</remoteHost>
      <port>4560</port>
  
      <!-- encoder is required -->
      <encoder class="net.logstash.logback.encoder.LogstashEncoder" />
  </appender>

  <appender-ref ref="stash" />
</configuration>

Unlike the UDP appender, an encoder must be configured for the TCP appenders. You can use a Logstash*Encoder, *EventCompositeJsonEncoder, or any other logback encoder. All of the output formatting options are configured at the encoder level.

Internally, the TCP appenders are asynchronous (using the LMAX Disruptor RingBuffer). All the encoding and TCP communication is delegated to a single writer thread. There is no need to wrap the TCP appenders with another asynchronous appender (such as AsyncAppender or LoggingEventAsyncDisruptorAppender).

All the configuration parameters (except for sub-appender) of the async appenders are valid for TCP appenders. For example, waitStrategyType and ringBufferSize.

The TCP appenders will never block the logging thread. If the RingBuffer is full (e.g. due to slow network, etc), then events will be dropped.

The TCP appenders will automatically reconnect if the connection breaks. However, events may be lost before Java's socket realizes the connection has broken.

If events occur infrequently, and the connection breaks consistently due to a server-side idle timeout, then you can enable keep alive functionality by configuring a keepAliveDuration like this:

  <appender name="stash" class="net.logstash.logback.appender.LogstashTcpSocketAppender">
      ...
      <keepAliveDuration>5 minutes</keepAliveDuration>
  </appender>

When the keepAliveDuration is set, then a keep alive message will be sent if an event has not occurred for the length of the duration. The keep alive message defaults to the system's line separator, but can be changed by setting the keepAliveMessage property.

To receive TCP input in logstash, configure a tcp input with the json codec in logstash's configuration like this:

input {
    tcp {
        port => 4560
        codec => json
    }
}

#### SSL

To use SSL, add an <ssl> sub-element within the <appender> element for the LogstashTcpSocketAppender or LogstashAccessTcpSocketAppender.

See the logback manual for how to configure SSL. SSL for the Logstash*TcpSocketAppenders are configured the same way as logback's SSLSocketAppender.

For example, to enable SSL using the JVM's default keystore/truststore, do the following:

  <appender name="stash" class="net.logstash.logback.appender.LogstashTcpSocketAppender">
      <!-- remoteHost and port are optional (default values shown) -->
      <remoteHost>127.0.0.1</remoteHost>
      <port>4560</port>
  
      <!-- encoder is required -->
      <encoder class="net.logstash.logback.encoder.LogstashEncoder" />
      
      <!-- Enable SSL using the JVM's default keystore/truststore -->
      <ssl/>
  </appender>

To use a different truststore, do the following:

  <appender name="stash" class="net.logstash.logback.appender.LogstashAccessTcpSocketAppender">
      <!-- remoteHost and port are optional (default values shown) -->
      <remoteHost>127.0.0.1</remoteHost>
      <port>4560</port>
  
      <!-- encoder is required -->
      <encoder class="net.logstash.logback.encoder.LogstashEncoder" />
      
      <!-- Enable SSL and use a different truststore -->
      <ssl>
          <trustStore>
              <location>classpath:server.truststore</location>
              <password>${server.truststore.password}</password>
          </trustStore>
      </ssl>
  </appender>

All the customizations that logback offers (such as configuring cipher specs, protocols, algorithms, providers, etc.) are supported by the Logback*TcpSocketAppenders.

See the logstash documentation for the tcp input for how to configure it to use SSL.

### Async Appenders

The *AsyncDisruptorAppender appenders are similar to logback's AsyncAppender, except that a LMAX Disruptor RingBuffer is used as the queuing mechanism, as opposed to a BlockingQueue. These async appenders can delegate to any other underlying logback appender.

For example:

  <appender name="async" class="net.logstash.logback.appender.LoggingEventAsyncDisruptorAppender">
    <appender class="ch.qos.logback.core.rolling.RollingFileAppender">
       ...
    </appender>
  </appender>

The async appenders will never block the logging thread. If the RingBuffer is full (e.g. due to slow network, etc), then events will be dropped.

By default, the BlockingWaitStrategy is used by the worker thread spawned by this appender. The BlockingWaitStrategy minimizes CPU utilization, but results in slower latency and throughput. If you need faster latency and throughput (at the expense of higher CPU utilization), consider a different wait strategy offered by the disruptor, such as SleepingWaitStrategy.

The wait strategy can be configured on the async appender using the waitStrategyType parameter, like this:

  <appender name="async" class="net.logstash.logback.appender.LoggingEventAsyncDisruptorAppender">
    <waitStrategyType>sleeping</waitStrategyType>
    <appender class="ch.qos.logback.core.rolling.RollingFileAppender">
       ...
    </appender>
  </appender>

The supported wait strategies are as follows:

Wait Strategy	Parameters	Implementation
blocking	none	BlockingWaitStrategy
busySpin	none	BusySpinWaitStrategy
liteBlocking	none	LiteBlockingWaitStrategy
sleeping	none	SleepingWaitStrategy
yielding	none	YieldingWaitStrategy
phasedBackoff{ spinTime, yieldTime, timeUnit, fallbackStrategy } e.g. phasedBackoff{10,60,seconds,blocking}	spinTime - Time to spin before yielding yieldTime - Time to yield before falling back to the fallbackStrategy timeUnit - Units of time for spin and yield timeouts. String name of a TimeUnit value (e.g. seconds) fallbackStrategy - String name of the wait strategy to fallback to after the timeouts have elapsed	PhasedBackoffWaitStrategy
timeoutBlocking{ timeout, timeUnit } e.g. timeoutBlocking{1,minutes}<	timeout - Time to block before throwing an exception timeUnit - Units of time for timeout. String name of a TimeUnit value (e.g. seconds)	TimeoutBlockingWaitStrategy

See AsyncDisruptorAppender for other configuration parameters (such as ringBufferSize, producerType, threadNamePrefix, daemon, and droppedWarnFrequency)

### Encoders / Layouts

You can use any of the encoders/layouts provided by the logstash-logback-encoder library with other logback appenders.

For example, to output LoggingEvents to a file, use the LogstashEncoder with the RollingFileAppender in your logback.xml like this:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <appender name="stash" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <filter class="ch.qos.logback.classic.filter.ThresholdFilter">
      <level>info</level>
    </filter>
    <file>/some/path/to/your/file.log</file>
    <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
      <fileNamePattern>/some/path/to/your/file.log.%d{yyyy-MM-dd}</fileNamePattern>
      <maxHistory>30</maxHistory>
    </rollingPolicy>
    <encoder class="net.logstash.logback.encoder.LogstashEncoder" />
  </appender>
  <root level="all">
    <appender-ref ref="stash" />
  </root>
</configuration>

To log AccessEvents to a file, configure your logback-access.xml like this:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
  <appender name="stash" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <file>/some/path/to/your/file.log</file>
    <encoder class="net.logstash.logback.encoder.LogstashAccessEncoder" />
  </appender>

  <appender-ref ref="stash" />
</configuration>

The LogstashLayout and LogstashAccessLayout can be configured the same way as the LogstashEncoder and LogstashAccessEncoder. All the other examples in this document use encoders, but the same options apply to the layouts as well.

To receive file input in logstash, configure a file input in logstash's configuration like this:

input {
  file {
    path => "/some/path/to/your/file.log"
    codec => "json"
  }
}

## LoggingEvent Fields

The following sections describe the fields included in the JSON output by default for LoggingEvents written by the

• LogstashEncoder
• LogstashLayout, and
• the logstash appenders

If you are using the composite encoders/layouts, then the fields written will vary by the providers you configure.

### Standard Fields

These fields will appear in every LoggingEvent unless otherwise noted. The field names listed here are the default field names. The field names can be customized (see Customizing Standard Field Names).

Field	Description
@timestamp	Time of the log event. (yyyy-MM-dd'T'HH:mm:ss.SSSZZ) See customizing timezone.
@version	Logstash format version (e.g. 1)
message	Formatted log message of the event
logger_name	Name of the logger that logged the event
thread_name	Name of the thread that logged the event
level	String name of the level of the event
level_value	Integer value of the level of the event
stack_trace	(Only if a throwable was logged) The stacktrace of the throwable. Stackframes are separated by line endings.
tags	(Only if tags are found) The names of any markers not explicitly handled. (e.g. markers from MarkerFactory.getMarker will be included as tags, but the markers from Markers will not.)

### MDC fields

By default, each entry in the Mapped Diagnostic Context (MDC) (org.slf4j.MDC) will appear as a field in the LoggingEvent.

This can be fully disabled by specifying <includeMdc>false</includeMdc>, in the encoder/layout/appender configuration.

You can also configure specific entries in the MDC to be included or excluded as follows:

<encoder class="net.logstash.logback.encoder.LogstashEncoder">
  <includeMdcKeyName>key1ToInclude</includeMdcKeyName>
  <includeMdcKeyName>key2ToInclude</includeMdcKeyName>
</encoder>

or

<encoder class="net.logstash.logback.encoder.LogstashEncoder">
  <excludeMdcKeyName>key1ToExclude</excludeMdcKeyName>
  <excludeMdcKeyName>key2ToExclude</excludeMdcKeyName>
</encoder>

When key names are specified for inclusion, then all other fields will be excluded. When key names are specified for exclusion, then all other fields will be included. It is a configuration error to specify both included and excluded key names.

### Context fields

By default, each property of Logback's Context (ch.qos.logback.core.Context) will appear as a field in the LoggingEvent. This can be disabled by specifying <includeContext>false</includeContext> in the encoder/layout/appender configuration.

### Caller Info Fields The encoder/layout/appender do not contain caller info by default. This can be costly to calculate and should be switched off for busy production environments.

To switch it on, add the includeCallerInfo property to the configuration.

<encoder class="net.logstash.logback.encoder.LogstashEncoder">
  <includeCallerInfo>true</includeCallerInfo>
</encoder>

When switched on, the following fields will be included in the log event:

Field	Description
caller_class_name	Fully qualified class name of the class that logged the event
caller_method_name	Name of the method that logged the event
caller_file_name	Name of the file that logged the event
caller_line_number	Line number of the file where the event was logged

### Custom Fields

In addition to the fields above, you can add other fields to the LoggingEvent either globally, or on an event-by-event basis.

#### Global Custom Fields

Add custom fields that will appear in every LoggingEvent like this :

<encoder class="net.logstash.logback.encoder.LogstashEncoder">
  <customFields>{"appname":"myWebservice","roles":["customerorder","auth"],"buildinfo":{"version":"Version 0.1.0-SNAPSHOT","lastcommit":"75473700d5befa953c45f630c6d9105413c16fe1"}}</customFields>
</encoder>

#### Event-specific Custom Fields

When logging a message, you can specify additional fields to add to the LoggingEvent by using the markers provided by Markers.

For example:

import static net.logstash.logback.marker.Markers.*

/*
 * Add "name":"value" to the json event.
 */
logger.info(append("name", "value"), "log message");

/*
 * Add "name1":"value1","name2":"value2" to the json event by using multiple markers.
 */
logger.info(append("name1", "value1").and(append("name2", "value2")), "log message");

/*
 * Add "name1":"value1","name2":"value2" to the json event by using a map.
 *
 * Note the values can be any object that can be serialized by Jackson's ObjectMapper
 * (e.g. other Maps, JsonNodes, numbers, arrays, etc)
 */
Map myMap = new HashMap();
myMap.put("name1", "value1");
myMap.put("name2", "value2");
logger.info(appendEntries(myMap), "log message");

/*
 * Add "array":[1,2,3] to the json event
 */
logger.info(appendArray("array", 1, 2, 3), "log message");

/*
 * Add "array":[1,2,3] to the json event by using raw json.
 * This allows you to use your own json seralization routine to construct the json output
 */
logger.info(appendRaw("array", "[1,2,3]"), "log message");

/*
 * Add any object that can be serialized by Jackson's ObjectMapper
 * (e.g. Maps, JsonNodes, numbers, arrays, etc)
 */
logger.info(append("object", myobject), "log message");

/*
 * Add fields of any object that can be unwrapped by Jackson's UnwrappableBeanSerializer.
 * i.e. The fields of an object can be written directly into the json output.
 * This is similar to the @JsonUnwrapped annotation.
 */
logger.info(appendFields(myobject), "log message");

See DEPRECATED.md for other deprecated ways of adding json to the output.

## AccessEvent Fields

The following sections describe the fields included in the JSON output by default for AccessEvents written by the

• LogstashAccessEncoder,
• LogstashAccessLayout, and
• the logstash access appenders.

If you are using the composite encoders/layouts, then the fields written will vary by the providers you configure.

### Standard Fields

These fields will appear in every AccessEvent unless otherwise noted. The field names listed here are the default field names. The field names can be customized (see Customizing Standard Field Names).

Field	Description
@timestamp	Time of the log event. (yyyy-MM-dd'T'HH:mm:ss.SSSZZ) See customizing timezone.
@version	Logstash format version (e.g. 1)
@message	Message in the form ${remoteHost} - ${remoteUser} [${timestamp}] "${requestUrl}" ${statusCode} ${contentLength}
@fields.method	HTTP method
@fields.protocol	HTTP protocol
@fields.status_code	HTTP status code
@fields.requested_url	Request URL
@fields.requested_uri	Request URI
@fields.remote_host	Remote host
@fields.HOSTNAME	another field for remote host (not sure why this is here honestly)
@fields.remote_user	Remote user
@fields.content_length	Content length
@fields.elapsed_time	Elapsed time in millis

### Header Fields

Request and response headers are not logged by default, but can be enabled by specifying a field name for them, like this:

<encoder class="net.logstash.logback.encoder.LogstashAccessEncoder">
  <fieldNames>
    <fieldsRequestHeaders>@fields.request_headers</fieldsRequestHeaders>
    <fieldsResponseHeaders>@fields.response_headers</fieldsResponseHeaders>
  </fieldNames>
</encoder>

See Customizing Standard Field Names) for more details.

## Customizing Standard Field Names

The standard field names above for LoggingEvents and AccessEvents can be customized by using the fieldNamesconfiguration element in the encoder or appender configuration.

For example:

<encoder class="net.logstash.logback.encoder.LogstashEncoder">
  <fieldNames>
    <timestamp>time</timestamp>
    <message>msg</message>
    ...
  </fieldNames>
</encoder>

Prevent a field from being output by setting the field name to [ignore].

For LoggingEvents, see LogstashFieldNames for all the field names that can be customized. Additionally, a separate set of shortened field names can be configured like this:

<encoder class="net.logstash.logback.encoder.LogstashEncoder">
  <fieldNames class="net.logstash.logback.fieldnames.ShortenedFieldNames"/>
</encoder>

For LoggingEvents, log the caller info, MDC properties, and context properties in sub-objects within the JSON event by specifying field names for caller, mdc, and context, respectively.

For AccessEvents, see LogstashAccessFieldNames for all the field names that can be customized

## Customizing TimeZone

By default, timestamps are logged in the default TimeZone of the host Java platform. You can change the timezone like this:

<encoder class="net.logstash.logback.encoder.LogstashEncoder">
  <timeZone>UTC</timeZone>
</encoder>

The value of the timeZone element can be any string accepted by java's TimeZone.getTimeZone(String id) method.

## Customizing JSON Factory and Generator

The JsonFactory and JsonGenerator used to serialize output can be customized by creating custom instances of JsonFactoryDecorator or JsonGeneratorDecorator, respectively.

For example, you could enable pretty printing like this:

public class PrettyPrintingDecorator implements JsonGeneratorDecorator {

    @Override
    public JsonGenerator decorate(JsonGenerator generator) {
        return generator.useDefaultPrettyPrinter();
    }

}

and then specify your decorator in the logback.xml file like this:

<encoder class="net.logstash.logback.encoder.LogstashEncoder">
  <jsonGeneratorDecorator class="your.package.PrettyPrintingDecorator"/>
</encoder>

## Customizing Logger Name Length

For LoggingEvents, you can shorten the logger name field length similar to the normal pattern style of %logger{36}. Examples of how it is shortened can be found here

<encoder class="net.logstash.logback.encoder.LogstashEncoder">
  <shortenedLoggerNameLength>36</shortenedLoggerNameLength>
</encoder>

## Customizing Stack Traces

For LoggingEvents, stack traces are formatted using logback's ExtendedThrowableProxyConverter by default. However, you can configure the encoder to use any ThrowableHandlingConverter to format stacktraces.

A powerful ShortenedThrowableConverter is included in the logstash-logback-encoder library to format stacktraces by:

• Limiting the number of stackTraceElements per throwable (applies to each individual throwable. e.g. caused-bys and suppressed)
• Limiting the total length in characters of the trace
• Abbreviating class names
• Filtering out consecutive unwanted stackTraceElements based on regular expressions.
• Using evaluators to determine if the stacktrace should be logged.
• Outputing in either 'normal' order (root-cause-last), or root-cause-first.

For example:

<encoder class="net.logstash.logback.encoder.LogstashEncoder">
  <throwableConverter class="net.logstash.logback.stacktrace.ShortenedThrowableConverter">
    <maxDepthPerThrowable>30</maxDepthPerThrowable>
    <maxLength>2048</maxLength>
    <shortenedClassNameLength>20</shortenedClassNameLength>
    <exclude>sun\.reflect\..*\.invoke.*</exclude>
    <exclude>net\.sf\.cglib\.proxy\.MethodProxy\.invoke</exclude>
    <evaluator class="myorg.MyCustomEvaluator"/>
    <rootCauseFirst>true</rootCauseFirst>
  </throwableConverter>
</encoder>

ShortenedThrowableConverter can even be used within a PatternLayout to format stacktraces in any non-JSON logs you may have.

## Prefix/Suffix

You can specify a prefix (written before the JSON object) and/or suffix (written after the JSON object), which may be required for the log pipeline you are using, such as:

• If you are using the Common Event Expression (CEE) format for syslog, you need to add the @cee: prefix.
• If you are using other syslog destinations, you might need to add the standard syslog headers.
• If you are using Loggly, you might need to add your customer token.

For example, to add standard syslog headers for syslog over UDP, configure the following:

<configuration>
  <conversionRule conversionWord="syslogStart" converterClass="ch.qos.logback.classic.pattern.SyslogStartConverter"/>
    
  <appender name="stash" class="net.logstash.logback.appender.LogstashSocketAppender">
    <host>MyAwesomeSyslogServer</host>
    <!-- port is optional (default value shown) -->
    <port>514</port>
    <prefix class="ch.qos.logback.core.encoder.LayoutWrappingEncoder">
      <layout class="ch.qos.logback.classic.PatternLayout">
        <pattern>%syslogStart{USER}</pattern>
      </layout>
    </prefix>
  </appender>
  
  ...
</configuration>

## Composite Encoder/Layout

If you want greater flexibility in the JSON format and data included in LoggingEvents and AccessEvents, use the LoggingEventCompositeJsonEncoder and AccessEventCompositeJsonEncoder (or the corresponding layouts).

These encoders/layouts are composed of one or more JSON providers that contribute to the JSON output. No providers are configured by default in the composite encoders/layouts. You must add the ones you want.

For example:

<encoder class="net.logstash.logback.encoder.LoggingEventCompositeJsonEncoder">
  <providers>
    <mdc/>
    <pattern>
      <pattern>
        {
          "timestamp": "%date{ISO8601}"
          "myCustomField": "fieldValue",
          "relative": "#asLong{%relative}"
        }
      </pattern>
    </pattern>
    <stackTrace>
      <throwableConverter class="net.logstash.logback.stacktrace.ShortenedThrowableConverter">
        <maxDepthPerThrowable>30</maxDepthPerThrowable>
        <maxLength>2048</maxLength>
        <shortenedClassNameLength>20</shortenedClassNameLength>
        <exclude>sun\.reflect\..*\.invoke.*</exclude>
        <exclude>net\.sf\.cglib\.proxy\.MethodProxy\.invoke</exclude>
        <evaluator class="myorg.MyCustomEvaluator"/>
        <rootCauseFirst>true</rootCauseFirst>
      </throwableConverter>
    </stackTrace>
  </providers>
</encoder>

The logstash-logback-encoder library contains many providers out-of-the-box, and you can even plug-in your own by extending JsonProvider. Each provider has its own configuration options to further customize it.

#### Providers for LoggingEvents

For LoggingEvents, the available providers and their configuration properties (defaults in parenthesis) are as follows:

Provider	Description/Properties
timestamp	Event timestamp fieldName - Output field name (@timestamp) pattern - Output format (yyyy-MM-dd'T'HH:mm:ss.SSSZZ) timeZone - Timezone (local timezone)
version	Logstash JSON format version fieldName - Output field name (@version) version - Output value (1)
message	Formatted log event message fieldName - Output field name (message)
loggerName	Name of the logger that logged the message fieldName - Output field name (logger_name) shortenedLoggerNameLength - Length to which the name will be attempted to be abbreviated (no abbreviation)
threadName	Name of the thread from which the event was logged fieldName - Output field name (thread_name)
logLevel	Logger level text (INFO, WARN, etc) fieldName - Output field name (level)
logLevelValue	Logger level numerical value fieldName - Output field name (level_value)
callerData	Outputs data about from where the logger was called (class/method/file/line) fieldName - Sub-object field name (no sub-object) classFieldName - Field name for class name (caller_class_name) methodFieldName - Field name for method name (caller_method_name) fileFieldName - Field name for file name (caller_file_name) lineFieldName - Field name for lin number (caller_line_number)
stackTrace	Stacktrace of any throwable logged with the event. Stackframes are separated by newline chars. fieldName - Output field name (stack_trace) throwableConverter - The ThrowableHandlingConverter to use to format the stacktrace (stack_trace)
context	Outputs entries from logback's context fieldName - Sub-object field name (no sub-object)
mdc	Outputs entries from the Mapped Diagnostic Context (MDC). Will include all entries by default. When key names are specified for inclusion, then all other fields will be excluded. When key names are specified for exclusion, then all other fields will be included. It is a configuration error to specify both included and excluded key names. fieldName - Sub-object field name (no sub-object) includeMdcKeyName - Name of keys to include (all) excludeMdcKeyName - Name of keys to include (none)
tags	Outputs logback markers as a comma separated list fieldName - Output field name (tags)
logstashMarkers	Used to output Logstash Markers as specified in Event-specific Custom Fields
pattern	Outputs fields from a configured JSON Object string, while substituting patterns supported by logback's PatternLayout. See Pattern JSON Provider pattern - JSON object string (no default)

#### Providers for AccessEvents

For AccessEvents, the available providers and their configuration properties (defaults in parenthesis) are as follows:

Provider	Description/Properties
timestamp	Event timestamp fieldName - Output field name (@timestamp) pattern - Output format (yyyy-MM-dd'T'HH:mm:ss.SSSZZ) timeZone - Timezone (local timezone)
version	Logstash JSON format version fieldName - Output field name (@version) version - Output value (1)
message	Message in the form `${remoteHost} - ${remoteUser} [${timestamp}] "${requestUrl}" ${statusCode} ${contentLength}` fieldName - Output field name (@message)
method	HTTP method fieldName - Output field name (@fields.method)
protocol	HTTP protocol fieldName - Output field name (@fields.protocol)
statusCode	HTTP status code fieldName - Output field name (@fields.status_code)
requestedUrl	Requested URL fieldName - Output field name (@fields.requested_url)
requestedUri	Requested URI fieldName - Output field name (@fields.requested_uri)
remoteHost	Remote Host fieldName - Output field name (@fields.remote_host)
remoteUser	Remote User fieldName - Output field name (@fields.remote_user)
contentLength	Content length fieldName - Output field name (@fields.content_length)
elapsedTime	Elapsed time in milliseconds fieldName - Output field name (@fields.elapsed_time)
pattern	Outputs fields from a configured JSON Object string, while substituting patterns supported by logback access's PatternLayout. See Pattern JSON Provider pattern - JSON object string (no default)

### Pattern JSON Provider

When used with a composite JSON encoder/layout, the pattern JSON provider can be used to define a template for a portion of the logged JSON output. The encoder/layout will populate values within the template. Every value in the template is treated as a pattern for logback's standard PatternLayout so it can be a combination of literal strings (for some constants) and various conversion specifiers (like %d for date).

The pattern string (configured within the pattern provider) must be a JSON Object. The contents of the JSON object are included within the logged JSON output.

This example...

<encoder class="net.logstash.logback.encoder.LoggingEventCompositeJsonEncoder">
  <providers>
    <!-- provides the timestamp -->
    <timestamp/>
    
    <!-- provides the version -->
    <version/>
    
    <!-- provides the fields in the configured pattern -->
    <pattern>
      <!-- the pattern that defines what to include -->
      <pattern>
        { "level": "%level" }
      </pattern>
    </pattern>
  </providers>
</encoder>

... will produce something like...

{
  "@timestamp":"...",
  "@version": 1,
  "level": "DEBUG"
}

The real power comes from the fact that there are lots of standard conversion specifiers so you can customise what is logged and how. For example, you could log a single specific value from MDC with %mdc{mykey}. Or, for access logs, you could log a single request header with %i{User-Agent}.

You can use nested objects and arrays in your pattern.

If you use a null, number, or a boolean constant in a pattern, it will keep its type in the resulting JSON. However, only the text values are searched for conversion patterns. And, as these patterns are sent through PatternLayout, the result is always a string even for something which you may feel should be a number - like for %b (bytes sent, in access logs).

You can either deal with the type conversion on the logstash side or you may use special operations provided by this encoder. The operations are:

• #asLong{...} - evaluates the pattern in curly braces and then converts resulting string to a long (or a null if conversion fails).
• #asDouble{...} - evaluates the pattern in curly braces and then converts resulting string to a double (or a null if conversion fails).

So this example...

<pattern>
  {
    "bytes_sent_str": "%b",
    "bytes_sent_long": "#asLong{%b}"
  }
</pattern>

...will produce something like...

{
  "bytes_sent_str": "1024",
  "bytes_sent_long": 1024
}

The value that is sent for bytes_sent_long is a number even though in your pattern it is a quoted text.

#### LoggingEvent patterns

For LoggingEvents, patterns from logback-classic's PatternLayout are supported.

For example:

<encoder class="net.logstash.logback.encoder.LoggingEventCompositeJsonEncoder">
  <providers>
    <timestamp/>
    <pattern>
      <pattern>
        {
        "custom_constant": "123",
        "tags": ["one", "two"],
        "logger": "%logger",
        "level": "%level",
        "thread": "%thread",
        "message": "%message",
...
        }
      </pattern>
    </pattern>
  </providers>
</encoder>

#### AccessEvent patterns

For AccessEvents, patterns from logback-access's PatternLayout are supported.

For example:

<encoder class="net.logstash.logback.encoder.AccessEventCompositeJsonEncoder">
  <providers>
    <pattern>
      <pattern>
        {
        "custom_constant": "123",
        "tags": ["one", "two"],
        "remote_ip": "%a",
        "status_code": "%s",
        "elapsed_time": "%D",
        "user_agent": "%i{User-Agent}",
        "accept": "%i{Accept}",
        "referer": "%i{Referer}",
        "session": "%requestCookie{JSESSIONID}",
...
        }
      </pattern>
    </pattern>
  </providers>
</encoder>

Note that the latest Logback (1.1.2 at the moment of writing), does not support deferred processing of request attributes. And because LogstashAccessTcpSocketAppender defers processing of the event to a background thread, you won't be able to use "%requestAttribute{name}" with TCP appender until this issue is fixed (or you build yourself a custom logback). http://jira.qos.ch/browse/LOGBACK-1033

There is also a special operation that can be used with this AccessEvents:

• #nullNA{...} - if the pattern in curly braces evaluates to a dash ("-"), it will be replaced with a null value.

You may want to use it because many of the PatternLayout conversion specifiers from logback-access will evaluate to "-" for non-existent value (for example for a cookie, header or a request attribute).

So the following pattern...

<pattern>
  {
    "default_cookie": "%requestCookie{MISSING}",
    "filtered_cookie": "#nullNA{%requestCookie{MISSING}}"
  }
</pattern>

...will produce...

{
  "default_cookie": "-",
  "filtered_cookie": null
}

## Debugging

During execution, the encoders/appenders/layouts provided in logstash-logback-encoder will add logback status messages to the logback StatusManager.

By default, logback only shows WARN/ERROR status messages on the console during configuration. No messages are output during actual operation (even if they are WARN/ERROR).

If you are having trouble identifying causes of problems (e.g. events are not getting delivered), then you can enable logback debugging or add a status listener as specified in the logback manual.

Profiling

Memory usage and performance of logstash-logback-encoder have been improved by addressing issues discovered with the help of the YourKit Java Profiler.

YourKit, LLC has graciously donated a free license of the YourKit Java Profiler to this open source project.

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