Log4j Spring Cloud Configuration

This module allows logging configuration files to be dynamically updated when new versions are available in Spring Cloud Configuration.

Overview

Spring Boot applications initialize logging 3 times. 1. SpringApplication declares a Logger. This Logger will be initialized using Log4j’s “normal” mechanisms. Thus a system property named log4j2.configurationFile will be checked to see if a specific configuration file has been provided, otherwise it will search for a configuration file on the classpath. The property may also be declare in log4j2.component.properties.

Usage

Log4j configuration files that specify a monitor interval of greater than zero will use polling to determine whether the configuration has been updated. If the monitor interval is zero then Log4j will listen for notifications from Spring Cloud Config and will check for configuration changes each time an event is generated. If the monitor interval is less than zero Log4j will not check for changes to the logging configuration.

When referencing a configuration located in Spring Cloud Config the configuration should be referenced similar to

log4j.configurationFile=http://host.docker.internal:8888/ConfigService/sampleapp/default/master/log4j2.xml

Log4j also supports Composite Configurations. The standard way to do that is to concatentate the paths to the files in a comma separated string. Unfortunately, Spring validates the URL being provided and commas are not allowed. Therefore, additional configurations must be supplied as “override” query parametes.

log4j.configurationFile=http://host.docker.internal:8888/ConfigService/sampleapp/default/master/log4j2.xml
?override=http://host.docker.internal:8888/ConfigService/sampleapp/default/master/log4j2-sampleapp.xml

Note that the location within the directory structure and how configuration files are located is completely dependent on the searchPaths setting in the Spring Cloud Config server.

When running in a docker container host.docker.internal may be used as the domain name to access an application running on the same hose outside of the docker container. Note that in accordance with Spring Cloud Config practices but the application, profile, and label should be specified in the url.

The Spring Cloud Config support also allows connections using TLS and/or basic authentication. When using basic authentication the userid and password may be specified as system properties, log4j2.component.properties or Spring Boot’s bootstrap.yml. The table below shows the alternate names that may be used to specify the properties. Any of the alternatives may be used in any configuration location.

Property	Alias	Spring-like alias	Purpose
log4j2.configurationUserName	log4j2.config.username	logging.auth.username	User name for basic authentication
log4j2.configurationPassword	log4j2.config.password	logging.auth.password	Password for basic authentication
log4j2.authorizationProvider	log4j2.config.authorizationProvider	logging.auth.authorizationProvider	Class used to create HTTP Authorization header

log4j2.configurationUserName=guest
log4j2.configurationPassword=guest

As noted above, Log4j supports accessing logging configuration from bootstrap.yml. As an example, to configure reading from a Spring Cloud Configuration service using basic authoriztion you can do:

spring:
  application:
    name: myApp
  cloud:
    config:
      uri: https://spring-configuration-server.mycorp.com
      username: appuser
      password: changeme

logging:
  config: classpath:log4j2.xml
  label: ${spring.cloud.config.label}

---
spring:
  profiles: dev

logging:
  config: https://spring-configuration-server.mycorp.com/myApp/default/${logging.label}/log4j2-dev.xml
  auth:
    username: appuser
    password: changeme

Note that Log4j currently does not directly support encrypting the password. However, Log4j does use Spring’s standard APIs to access properties in the Spring configuration so any customizations made to Spring’s property handling would apply to the properties Log4j uses as well.

If more extensive authentication is required an AuthorizationProvider can be implemented and the fully qualified class name in the log4j2.authorizationProvider system property, in log4j2.component.properties or in Spring’s bootstrap.yml using either the log4j2.authorizationProvider key or with the key logging.auth.authorizationProvider.

TLS can be enabled by adding the following system properties or defining them in log4j2.component.properties

Property	Optional or Default Value	Description
log4j2.trustStoreLocation	Optional	The location of the trust store. If not provided the default trust store will be used.
log4j2.trustStorePassword	Optional	Password needed to access the trust store.
log4j2.trustStorePasswordFile	Optional	The location of a file that contains the password for the trust store.
log4j2.trustStorePasswordEnvironmentVariable	Optional	The name of the environment variable that contains the trust store password.
log4j2.trustStoreKeyStoreType	Required if keystore location provided	The type of key store.
log4j2.trustStoreKeyManagerFactoryAlgorithm	Optional	Java cryptographic algorithm.
log4j2.keyStoreLocation	Optional	The location of the key store. If not provided the default key store will be used.
log4j2.keyStorePassword	Optional	Password needed to access the key store.
log4j2.keyStorePasswordFile	Optional	The location of a file that contains the password for the key store.
log4j2.keyStorePasswordEnvironmentVariable	Optional	The name of the environment variable that contains the key store password.
log4j2.keyStoreType	Required if trust store location provided.	The type of key store.
log4j2.keyStoreKeyManagerFactoryAlgorithm	Optional	Java cryptographic algorithm.
log4j2.sslVerifyHostName	false	true or false

Requirements

The Log4j 2 Spring Cloud Configuration integration has a dependency on Log4j 2 API, Log4j 2 Core, and Spring Cloud Configuration versions 2.0.3.RELEASE or 2.1.1.RELEASE or later versions it either release series. For more information, see Runtime Dependencies.