Java Logging Support for Cloud Foundry

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Summary

This is a collection of support libraries for Java applications (Java 11 and above) that serves three main purposes:

1. Provide means to emit structured application log messages
2. Instrument parts of your application stack to collect request metrics
3. Allow auto-configuration of OpenTelemetry exporters.

The libraries started out to support applications running on Cloud Foundry. This integration has become optional. The library can be used in any runtime environment such as Kubernetes or Kyma.

When we say structured, we actually mean in JSON format. In that sense, it shares ideas with logstash-logback-encoder, but takes a simpler approach as we want to ensure that these structured messages adhere to standardized formats. With such standardized formats in place, it becomes much easier to ingest, process and search such messages in log analysis stacks such as ELK.

If you're interested in the specifications of these standardized formats, you may want to have a closer look at the fields.yml files in the beats folder.

While logstash-logback-encoder is tied to logback, we've tried to keep implementation neutral and have implemented the core functionality on top of slf4j, but provided implementations for both logback and log4j2 (and we're open to contributions that would support other implementations).

The instrumentation part is currently focusing on providing request filters for Java Servlets, but again, we're open to contributions for other APIs and frameworks.

Lastly, there is also a project on node.js logging support.

Features and dependencies

As you can see from the structure of this repository, we're not providing one uber JAR that contains everything, but provide each feature separately. We also try to stay away from wiring up too many dependencies by tagging almost all of them as provided. As a consequence, it's your task to get all runtime dependencies resolved in your application POM file.

All in all, you should do the following:

1. Make up your mind which features you actually need.
2. Adjust your Maven dependencies accordingly.
3. Pick your favorite logging implementation. And
4. Adjust your logging configuration accordingly.

Let's say you want to make use of the servlet filter feature, then you need to add the following dependency to your POM with property cf-logging-version referring to the latest nexus version (currently 4.0.0-RC1):

<properties>
	<cf-logging-version>4.0.0-RC1</cf-logging-version>
</properties>

<dependency>
  <groupId>com.sap.hcp.cf.logging</groupId>
  <artifactId>cf-java-logging-support-servlet</artifactId>
  <version>${cf-logging-version}</version>
</dependency>

This feature only depends on the servlet API which you have included in your POM anyhow. You can find more information about the servlet filter feature (like e.g. how to adjust the web.xml) in the Wiki.

Implementation variants and logging configurations

The core feature (on which all other features rely) is just using the org.slf4j API, but to actually get logs written, you need to pick an implementation feature. As stated above, we have two implementations:

• cf-java-logging-support-logback based on logback, and
• cf-java-logging-support-log4j2 based on log4j2.

Again, we don't include dependencies to those implementation backends ourselves, so you need to provide the corresponding dependencies in your POM file:

Using logback:

<dependency>
	<groupId>com.sap.hcp.cf.logging</groupId>
  	<artifactId>cf-java-logging-support-logback</artifactId>
  	<version>${cf-logging-version}</version>
</dependency>

<dependency>
  	<groupId>ch.qos.logback</groupId>
   	<artifactId>logback-classic</artifactId>
   	<version>1.2.11</version>
 </dependency>

Using log4j2:

<dependency>
	<groupId>com.sap.hcp.cf.logging</groupId>
  	<artifactId>cf-java-logging-support-log4j2</artifactId>
  	<version>${cf-logging-version}</version>
</dependency>
<dependency>
	<groupId>org.apache.logging.log4j</groupId>
	<artifactId>log4j-slf4j-impl</artifactId>
	<version>2.20.0</version>
</dependency>
	<dependency>
	<groupId>org.apache.logging.log4j</groupId>
	<artifactId>log4j-core</artifactId>
	<version>2.20.0</version>
</dependency>

As they have slightly differ in configuration, you again will need to do that yourself. But we hope that we've found an easy way to accomplish that. The one thing you have to do is pick our encoder in your logback.xml if you're using logback or our layout in your log4j2.xmlif you're using log4j2.

Here are the minimal configurations you'd need:

logback.xml:

<configuration debug="false" scan="false">
	<appender name="STDOUT-JSON" class="ch.qos.logback.core.ConsoleAppender">
       <encoder class="com.sap.hcp.cf.logback.encoder.JsonEncoder"/>
    </appender>
    <!-- for local development, you may want to switch to a more human-readable layout -->
    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%date %-5level [%thread] - [%logger] [%mdc] - %msg%n</pattern>
        </encoder>
    </appender>
    <root level="${LOG_ROOT_LEVEL:-WARN}">
       <!-- Use 'STDOUT' instead for human-readable output -->
       <appender-ref ref="STDOUT-JSON" />
    </root>
  	<!-- request metrics are reported using INFO level, so make sure the instrumentation loggers are set to that level -->
    <logger name="com.sap.hcp.cf" level="INFO" />
</configuration>

log4j2.xml:

<Configuration
   status="warn" strict="true">
	<Appenders>
        <Console name="STDOUT-JSON" target="SYSTEM_OUT" follow="true">
            <JsonPatternLayout charset="utf-8"/>
        </Console>
        <Console name="STDOUT" target="SYSTEM_OUT" follow="true">
            <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} [%mdc] - %msg%n"/>
        </Console>
	</Appenders>
  <Loggers>
     <Root level="${LOG_ROOT_LEVEL:-WARN}">
        <!-- Use 'STDOUT' instead for human-readable output -->
        <AppenderRef ref="STDOUT-JSON" />
     </Root>
  	 <!-- request metrics are reported using INFO level, so make sure the instrumentation loggers are set to that level -->
     <Logger name="com.sap.hcp.cf" level="INFO"/>
  </Loggers>
</Configuration>

Dynamic Log Levels

This library provides the possibility to change the log-level threshold for a single thread by adding a token in the header of a request. A detailed description about how to apply this feature can be found here.

Logging Stacktraces

Stacktraces can be logged within one log message. Further details can be found here.

Sample Applications

In order to illustrate how the different features are used, this repository includes one sample application:

• a Spring Boot implementation in the ./sample-spring-boot folder

Documentation

More info on the actual implementation can be found in the Wiki.

Licensing

Please see our LICENSE for copyright and license information. Detailed information including third-party components and their licensing/copyright information is available via the REUSE tool.