docs/modules/servers/partials/operate/logging.adoc

We recommend to closely monitoring *ERROR* and *WARNING* logs. Those
logs should be considered not normal.

If you encounter some suspicious logs:

* If you have any doubt about the log being caused by a bug in James
source code, please reach us via the bug tracker, the user mailing list or our Gitter channel (see our
http://james.apache.org/#second[community page])
* They can be due to insufficient performance from tier applications (eg
{backend-name} timeouts). In such case we advise you to conduct a close
review of performances at the tier level.

Leveraging filters in Kibana discover view can help to filter out
''already known'' frequently occurring logs.

When reporting ERROR or WARNING logs, consider adding the full logs, and
related data (eg the raw content of a mail triggering an issue) to the
bug report in order to ease resolution.

== Logging configuration

{server-name} uses link:http://logback.qos.ch/[logback] as a logging library
and link:https://docs.fluentbit.io/[FluentBit] as centralize logging.

Information about logback configuration can be found
link:http://logback.qos.ch/manual/configuration.html[here].

== Structured logging

=== Pushing logs to ElasticSearch

{server-name} leverages the use of MDC in order to achieve structured logging,
and better add context to the logged information. We furthermore ship
link:https://github.com/linagora/logback-elasticsearch-appender[Logback Elasticsearch Appender]
on the classpath to easily allow direct log indexation in
link:https://www.elastic.co/elasticsearch[ElasticSearch].

Here is a sample `conf/logback.xml` configuration file for logback with the following
pre-requisites:

* Logging both in an unstructured fashion on the console and in a structured fashion in ElasticSearch
* Logging ElasticSearch Log appender logs in the console

Configuration for pushing log direct to ElasticSearch

* Logging ElasticSearch Log appender logs in the console

....
<?xml version="1.0" encoding="UTF-8"?>
<configuration scan="true" scanPeriod="30 seconds">

        <contextListener class="ch.qos.logback.classic.jul.LevelChangePropagator">
                <resetJUL>true</resetJUL>
        </contextListener>

        <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
                <encoder>
                        <pattern>%d{yyyy.MM.dd HH:mm:ss.SSS} %highlight([%-5level]) %logger{15} - %msg%n%rEx</pattern>
                        <immediateFlush>false</immediateFlush>
                </encoder>
        </appender>

        <appender name="ELASTIC" class="com.linagora.logback.elasticsearch.ElasticsearchAppender">
            <url>http://elasticsearch:9200/_bulk</url>
            <index>logs-james-%date{yyyy.MM.dd}</index>
            <type>tester</type>
            <includeMdc>true</includeMdc>
            <excludedMdcKeys>host</excludedMdcKeys>
            <errorLoggerName>es-error-logger</errorLoggerName>
            <properties>
                <property>
                    <name>host</name>
                    <value>${HOSTNAME}</value>
                    <allowEmpty>false</allowEmpty>
                </property>
                <property>
                    <name>severity</name>
                    <value>%level</value>
                </property>
                <property>
                    <name>thread</name>
                    <value>%thread</value>
                </property>
                <property>
                    <name>stacktrace</name>
                    <value>%ex</value>
                </property>
                <property>
                    <name>logger</name>
                    <value>%logger</value>
                </property>
            </properties>
            <headers>
                <header>
                    <name>Content-Type</name>
                    <value>application/json</value>
                </header>
            </headers>
        </appender>

        <root level="WARN">
                <appender-ref ref="ELASTIC" />
        </root>

        <logger name="es-error-logger" level="DEBUG" additivity="false">
            <appender-ref ref="CONSOLE" />
        </logger>

        <logger name="org.apache.james" level="INFO" />

</configuration>
....

=== Using FluentBit as a log forwarder

==== Using Docker

{server-name} leverages the use of MDC in order to achieve structured logging, and better add context to the logged information. We furthermore ship json logs to file with RollingFileAppender on the classpath to easily allow FluentBit to directly tail the log file.
Here is a sample conf/logback.xml configuration file for logback with the following pre-requisites:

Logging in a structured json fashion and write to file for centralizing logging.
Centralize logging third party like FluentBit can tail from logging’s file then filter/process and put in to OpenSearch

....
<?xml version="1.0" encoding="UTF-8"?>
<configuration>

        <contextListener class="ch.qos.logback.classic.jul.LevelChangePropagator">
                <resetJUL>true</resetJUL>
        </contextListener>

        <appender name="LOG_FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
                <rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
                        <fileNamePattern>logs/james.%d{yyyy-MM-dd}.%i.log</fileNamePattern>
                        <maxHistory>1</maxHistory>
                        <totalSizeCap>200MB</totalSizeCap>
                        <maxFileSize>100MB</maxFileSize>
                </rollingPolicy>

                <encoder class="ch.qos.logback.core.encoder.LayoutWrappingEncoder">
                    <layout class="ch.qos.logback.contrib.json.classic.JsonLayout">
                        <timestampFormat>yyyy-MM-dd'T'HH:mm:ss.SSSX</timestampFormat>
                        <timestampFormatTimezoneId>Etc/UTC</timestampFormatTimezoneId>

                        <!-- Importance for handling multiple lines log -->
                        <appendLineSeparator>true</appendLineSeparator>

                        <jsonFormatter class="ch.qos.logback.contrib.jackson.JacksonJsonFormatter">
                            <prettyPrint>false</prettyPrint>
                        </jsonFormatter>
                    </layout>
                </encoder>
        </appender>

        <root level="INFO">
            <appender-ref ref="LOG_FILE" />
        </root>

</configuration>
....

First you need to create a `logs` folder, then mount it to James container and to FluentBit.

docker-compose:

include::{docker-compose-code-block-sample}[]

FluentBit config as:
the `Host opensearch` pointing to `opensearch` service in docker-compose file.
....
[SERVICE]
    Parsers_File    /fluent-bit/etc/parsers.conf

[INPUT]
    name                    tail
    path                    /fluent-bit/log/*.log
    Parser                  docker
    docker_mode             on
    buffer_chunk_size       1MB
    buffer_max_size         1MB
    mem_buf_limit           64MB
    Refresh_Interval        30

[OUTPUT]
    Name  stdout
    Match *


[OUTPUT]
    Name  es
    Match *
    Host opensearch
    Port 9200
    Index fluentbit
    Logstash_Format On
    Logstash_Prefix fluentbit-james
    Type docker
....

FluentBit Parser config:
....
[PARSER]
  Name         docker
  Format       json
  Time_Key     timestamp
  Time_Format  %Y-%m-%dT%H:%M:%S.%LZ
  Time_Keep    On
  Decode_Field_As   escaped_utf8    log    do_next
  Decode_Field_As   escaped         log    do_next
  Decode_Field_As   json            log
....

==== Using Kubernetes

If using James in a Kubernetes environment, you can just append the logs to the console in a JSON formatted way 
using Jackson to easily allow FluentBit to directly tail them.

Here is a sample conf/logback.xml configuration file for achieving this:

....
<?xml version="1.0" encoding="UTF-8"?>
<configuration>

        <contextListener class="ch.qos.logback.classic.jul.LevelChangePropagator">
                <resetJUL>true</resetJUL>
        </contextListener>

        <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
                <encoder class="ch.qos.logback.core.encoder.LayoutWrappingEncoder">
                    <layout class="ch.qos.logback.contrib.json.classic.JsonLayout">
                        <timestampFormat>yyyy-MM-dd'T'HH:mm:ss.SSSX</timestampFormat>
                        <timestampFormatTimezoneId>Etc/UTC</timestampFormatTimezoneId>

                        <!-- Importance for handling multiple lines log -->
                        <appendLineSeparator>true</appendLineSeparator>

                        <jsonFormatter class="ch.qos.logback.contrib.jackson.JacksonJsonFormatter">
                            <prettyPrint>false</prettyPrint>
                        </jsonFormatter>
                    </layout>
                </encoder>
        </appender>

        <root level="INFO">
                <appender-ref ref="CONSOLE" />
        </root>

</configuration>
....

Regarding FluentBit on Kubernetes, you need to install it as a DaemonSet. Some official template exist
with FluentBit outputting logs to OpenSearch. For more information on how to install it,
with your cluster, you can look at this https://docs.fluentbit.io/manual/installation/kubernetes[documentation].

As stated by the https://docs.fluentbit.io/manual/installation/kubernetes#details[detail] of the
official documentation, FluentBit is configured to consume out of the box logs from containers
on the same running node. So it should scrap your James logs without extra configuration.