[jira] [Commented] (LOG4J2-3621) Log4J 2.19 breaks contract of order of loading of System Properties

["Adwait Kumar Singh (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LOG4J2-3621?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17684303#comment-17684303 ] 

Adwait Kumar Singh commented on LOG4J2-3621:
--------------------------------------------

[~pkarwasz] Can I use a simpler approach of creating a new {{LegacySystemPropertiesSource}} which would have priority of 1. I having some trouble getting your approach to work with the existing tests.

> Log4J 2.19 breaks contract of order of loading of System Properties
> -------------------------------------------------------------------
>
>                 Key: LOG4J2-3621
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-3621
>             Project: Log4j 2
>          Issue Type: Bug
>          Components: Configuration
>    Affects Versions: 2.19.0, 2.19.1
>            Reporter: Adwait Kumar Singh
>            Priority: Major
>
> [This change|https://github.com/apache/logging-log4j2/pull/742] broke one of our systems on upgrading to 2.19.
> In our applications we had both LOG4J_CONFIGURATION_FILE environment variable as well as log4j.configurationFile system property set.
> In version 2.17.2 "log4j.configurationFile" gets priority vs in 2.19 "LOG4J_CONFIGURATION_FILE" gets priority. This also breaks the contract mentioned in the [documentation|https://logging.apache.org/log4j/2.x/manual/configuration.html#SystemProperties].
> This is happening because of the normalization code here, [https://github.com/apache/logging-log4j2/blob/release-2.x/log4j-api/src/main/java/org/apache/logging/log4j/util/PropertiesUtil.java#L503-L526]
>  
> When we are trying to normalize, we are checking if the source contains the normalKey. In case both log4j.configurationFile and LOG4J_CONFIGURATION_FILE are present, the following sequence happens,
>  # log4j.configurationFile does not get inserted into the normalized map because the normal key is log4j2.configurationFile which is not present in the SystemPropertiesSource.
>  # Then when we hit the EnvironmentPropertiesSource, log4j.configurationFile is normalized to LOG4J_CONFIGURATION_FILE and then an entry is made in the normalized map with key = log4j.configurationFile, but value of LOG4J_CONFIGURATION_FILE.
>  # During look up with first look into normalized map, so now we got the wrong value (EnvironmentVariable instead of SystemProperty).
>  
> I am aware changing "log4j.configurationFile" to "log4j2.configurationFile" can fix the issue, however this is clearly a backward incompatible change which will require this change across a lot of consumers who want to upgrade to log4j 2.19
> I can think of two ways to fix this,
>  # We make an entry into the normalized map with the actual key if the normalized key is not present in the source, OR
>  # While fetching we prefer literal map over normalized map.
> Would like to know which of the approaches would be better, can raise a PR accordingly.



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