Dynamic Logback Log Level in Spring Boot

There are times where we want to create a dynamic configuration for our logging level. Lets say for most of cases, logger with level INFO is sufficient enough, but we want a much more detail logger such as DEBUG or TRACE for debugging purpose.

We can achieve that condition by using a dynamic configuration in Logback. This is how we do it, we’ll start with using a specific logging library called Logback.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.edw</groupId>
    <artifactId>springboot-and-logback-xml</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>17</maven.compiler.source>
        <maven.compiler.target>17</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.0.4</version>
        <relativePath/>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

And create a file called logback.xml,

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

    <property name="APP_LOG_LEVEL" value="${APP_LOG_LEVEL:-INFO}" />
    <property name="ROOT_LOG_LEVEL" value="${ROOT_LOG_LEVEL:-WARN}" />
    
    <appender name="CONSOLE"
              class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
            <charset>utf8</charset>
        </encoder>
    </appender>

    <logger name="com.edw" level="${APP_LOG_LEVEL}" additivity="false">
        <appender-ref ref="CONSOLE" />
    </logger>

    <root level="${ROOT_LOG_LEVEL}">
        <appender-ref ref="CONSOLE" />
    </root>
</configuration>

We can test by using below Java code where we create two different logging line with different log level,

package com.edw.controller;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.HashMap;

@RestController
public class IndexController {

    private static final Logger logger = LoggerFactory.getLogger(IndexController.class);

    @GetMapping("/")
    public HashMap getIndexPage() {
        logger.debug("we are at index page using {}", "DEBUG");
        logger.info("we are at index page using {}", "INFO");

        return new HashMap() {{
            put("hello", "world");
        }};
    }
}

We can run the project using default command and see default log outputs

$  java -jar springboot-and-logback-xml-1.0-SNAPSHOT.jar

  .   ____          _            __ _ _    
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \   
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \  
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) ) 
  '  |____| .__|_| |_|_| |_\__, | / / / /  
 =========|_|==============|___/=/_/_/_/   
 :: Spring Boot ::                (v3.0.4) 

14:12:49.321 [main] INFO  com.edw.Main - Starting Main v1.0-SNAPSHOT using Java 17.0.6 with PID 13480 
14:12:49.326 [main] INFO  com.edw.Main - No active profile set, falling back to 1 default profile: "default" 
14:12:51.122 [main] INFO  com.edw.Main - Started Main in 2.283 seconds (process running for 2.983) 
14:13:02.489 [http-nio-8080-exec-1] INFO  com.edw.controller.IndexController - we are at index page using INFO 

However for a much more detail outputs, we can use below command with configured “APP_LOG_LEVEL” and “ROOT_LOG_LEVEL”

$ java -DAPP_LOG_LEVEL=DEBUG -DROOT_LOG_LEVEL=INFO -jar springboot-and-logback-xml-1.0-SNAPSHOT.jar

  .   ____          _            __ _ _    
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \   
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \  
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) ) 
  '  |____| .__|_| |_|_| |_\__, | / / / /  
 =========|_|==============|___/=/_/_/_/   
 :: Spring Boot ::                (v3.0.4) 
 
14:15:40.353 [main] INFO  com.edw.Main - Starting Main v1.0-SNAPSHOT using Java 17.0.6 with PID 9004 
14:15:40.356 [main] DEBUG com.edw.Main - Running with Spring Boot v3.0.4, Spring v6.0.6                      
14:15:40.357 [main] INFO  com.edw.Main - No active profile set, falling back to 1 default profile: "default" 
14:15:41.774 [main] INFO  o.s.b.w.e.tomcat.TomcatWebServer - Tomcat initialized with port(s): 8080 (http) 
14:15:41.788 [main] INFO  o.a.coyote.http11.Http11NioProtocol - Initializing ProtocolHandler ["http-nio-8080"] 
14:15:41.789 [main] INFO  o.a.catalina.core.StandardService - Starting service [Tomcat]
14:15:41.789 [main] INFO  o.a.catalina.core.StandardEngine - Starting Servlet engine: [Apache Tomcat/10.1.5]
14:15:41.903 [main] INFO  o.a.c.c.C.[Tomcat].[localhost].[/] - Initializing Spring embedded WebApplicationContext 
14:15:41.905 [main] INFO  o.s.b.w.s.c.ServletWebServerApplicationContext - Root WebApplicationContext: initialization completed in 1449 ms 
14:15:42.365 [main] INFO  o.a.coyote.http11.Http11NioProtocol - Starting ProtocolHandler ["http-nio-8080"] 
14:15:42.404 [main] INFO  o.s.b.w.e.tomcat.TomcatWebServer - Tomcat started on port(s): 8080 (http) with context path '' 
14:15:42.425 [main] INFO  com.edw.Main - Started Main in 2.604 seconds (process running for 3.422) 
14:17:29.454 [http-nio-8080-exec-1] INFO  o.a.c.c.C.[Tomcat].[localhost].[/] - Initializing Spring DispatcherServlet 'dispatcherServlet' 
14:17:29.455 [http-nio-8080-exec-1] INFO  o.s.web.servlet.DispatcherServlet - Initializing Servlet 'dispatcherServlet' 
14:17:29.456 [http-nio-8080-exec-1] INFO  o.s.web.servlet.DispatcherServlet - Completed initialization in 1 ms
14:17:29.490 [http-nio-8080-exec-1] DEBUG com.edw.controller.IndexController - we are at index page using DEBUG 
14:17:29.492 [http-nio-8080-exec-1] INFO  com.edw.controller.IndexController - we are at index page using INFO 

For Kubernetes delployments, we can also use below environment variables

  env:
	- name: APP_LOG_LEVEL
	  value: DEBUG
	- name: ROOT_LOG_LEVEL
	  value: INFO