<% set_title("How", product_name, "Logging Works") %>

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<%=vars.product_name_long%> uses Apache Log4j 2 as the basis for its logging system.

<%=vars.product_name%> uses [Apache Log4j 2](http://logging.apache.org/log4j/2.x/) API and Core libraries as the basis for its logging system. Log4j 2 API is a popular and powerful front-end logging API used by all the <%=vars.product_name%> classes to generate log statements. Log4j 2 Core is a backend implementation for logging; you can route any of the front-end logging API libraries to log to this backend. <%=vars.product_name%> uses the Core backend to run two custom Log4j 2 Appenders: **AlertAppender** and **LogWriterAppender**.

<%=vars.product_name%> has been tested with Log4j 2.1.

**Note:**
For this reason, <%=vars.product_name%> now always requires the following JARs to be in the classpath: `log4j-api-2.1.jar`, `log4j-core-2.1.jar`. Both of these JARs are distributed in the `$GEMFIRE/lib` directory and included in the appropriate `*-dependencies.jar` convenience libraries.

**AlertAppender** is the component that generates <%=vars.product_name%> alerts that are then managed by the JMX Management and Monitoring system. See [Notification Federation](../management/notification_federation_and_alerts.html#topic_212EE5A2ABAB4E8E8EF71807C9ECEF1A) for more details.

**LogWriterAppender** is the component that is configured by all the `log-*` <%=vars.product_name%> properties such as `log-file`, `log-file-size-limit` and `log-disk-space-limit`.

Both of these appenders are created and controlled programmatically. You configure their behavior with the `log-*` <%=vars.product_name%> properties and the alert level that is configured within the JMX Management & Monitoring system. These appenders do not currently support configuration within a `log4j2.xml` config file.

Advanced users may wish to define their own `log4j2.xml`. See [Advanced Users—Configuring Log4j 2 for <%=vars.product_name%>](configuring_log4j2.html) for more details.


