[jira] [Commented] (LOG4J2-3366) Fix order of property sources

["Piotr P. Karwasz (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LOG4J2-3366?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17482997#comment-17482997 ] 

Piotr P. Karwasz commented on LOG4J2-3366:
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I noticed now, that documentation and Javadoc disagree on how to interpret the priority of the sources:
 * the [documentation|https://logging.apache.org/log4j/2.x/manual/configuration.html#SystemProperties] says: _Properties can be overridden by sources with a lower number priority (e.g.., -100 comes before 100)._
 * the [Javadoc|https://logging.apache.org/log4j/2.x/log4j-api/apidocs/org/apache/logging/log4j/util/PropertySource.html#getPriority--] says: _A higher value means that the source will be applied later so as to take precedence over other property sources._

> Fix order of property sources
> -----------------------------
>
>                 Key: LOG4J2-3366
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-3366
>             Project: Log4j 2
>          Issue Type: Improvement
>    Affects Versions: 2.10.0
>            Reporter: Piotr P. Karwasz
>            Priority: Minor
>
> The current order of system property sources (cf. [documentation|https://logging.apache.org/log4j/2.x/manual/configuration.html#SystemProperties]) is rather unnatural, because:
>  # It gives a higher priority to environment variables than Java system properties. Java system properties apply to a single JVM, whereas environment variables might be shared between processes.
>  # It mixes up property sources accessible to system administrators and those accessible only to programmers (`log4j2.component.properties`).
> IMHO Log4j should prioritize the sources accessible to system administrators over `log4j2.component.properties`, hence allowing them to easily override the defaults established by developers. It should also prioritize Java system properties over environment variables. This is what, e.g. [Spring Boot does|https://docs.spring.io/spring-boot/docs/current/reference/html/features.html#features.external-config]. I propose the following order:
>  # System properties,
>  # Environment variables,
>  # `log4j2.component.properties` as failover.
> While technically this would be a breaking change, the official property source order never worked and bug LOG4J2-3193 was filed only recently. This proves that almost no one configures the same property in more than one source.



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