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https://issues.apache.org/jira/browse/SOLR-15960?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17757608#comment-17757608
]
Jan Høydahl commented on SOLR-15960:
------------------------------------
I did a similar stunt in otel plugin, a method {{{}envOrSysprop{}}}:
[https://github.com/apache/solr/blob/main/solr/modules/opentelemetry/src/java/org/apache/solr/opentelemetry/OtelTracerConfigurator.java#L138-L159]
{code:java}
/**
* Returns system property if found, else returns environment variable, or null
if none found.
*
* @param envName the environment to look for
* @return the resolved value
*/
String getEnvOrSysprop(String envName) {
String envValue = currentEnv.get(envName);
String propValue = System.getProperty(envNameToSyspropName(envName));
return propValue != null ? propValue : envValue;
}
/**
* In OTEL Java SDK there is a convention that the java property name for
OTEL_FOO_BAR is
* otel.foo.bar
*
* @param envName the environmnet name to convert
* @return the corresponding sysprop name
*/
static String envNameToSyspropName(String envName) {
return envName.toLowerCase(Locale.ROOT).replace("_", ".");
} {code}
> Unified use of system properties and environment variables
> ----------------------------------------------------------
>
> Key: SOLR-15960
> URL: https://issues.apache.org/jira/browse/SOLR-15960
> Project: Solr
> Issue Type: Improvement
> Reporter: Jan Høydahl
> Priority: Major
>
> We have a lot of boiler-plate code in Solr related to resolving configuration
> from config-files, system properties and environment variables.
> The main pattern so far has been to load a config from an xml file, which
> uses system property variables like {{{}$\{myVar{}}}}. All the environment
> variables that we expose in {{solr.in.sh}} are converted to system.properties
> in {{bin/solr}} and inside of Solr we only care about sys.props. This has
> served us quite well, but is also has certain disadvantages:
> * Naming mismatches. You have one config name in the xml file, one as system
> property and yet another for environment variable.
> * Duplicate code to deal with type conversion, and converting comma
> separated lists from env.var into Java lists
> * Every new config option needs to touch {{{}bin/solr{}}}, {{bin/solr.cmd}}
> and often more.
> In the world of containers and k8s, we want to configure almost every aspect
> of an app using environment variables. It is sometimes also more secure than
> passing sys.props on the cmdline since they won't show up in a "ps".
> So this is a proposal to unify all Solr's configs in a more structured way
> * Make naming a convention. All env.variable should be uppercase with format
> {{SOLR_X_Y}} and all sys.propos should be lowercase with the format
> {{solr.x.y}}. Perhaps {{solr.camelCase}} should map to {{SOLR_CAMEL_CASE}},
> or we discourage camel case in favour of dots.
> * Add a central {{ConfigResolver}} class to Solr that can answer e.g.
> {{getInt("solr.my.number")}} and it would return either prop
> {{solr.my.number}} or {{SOLR_MY_NUMBER}}. Similar for String, bool etc, and
> with fallback-values
> * List support, e.g. {{getListOfStrings("solr.modules")}} and it would
> return a {{List<String>}} from either {{solr.modules}} or {{SOLR_MODULES}},
> supporting comma-separated, custom separator and why not also json list
> format ["foo","bar"]?
> A pitfall of using environment variables directly is testing, since env.vars
> are immutable. I suggest we solve this by reading all {{SOLR_*}}
> env.variables on startup and inserting them into a static, mutable map
> somewhere which is the single source of truth for env.vars. Then we can ban
> the use of {{System.getenv()}}.
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