Merge pull request #292 from BhHaipls/feat-support-host-and-port-from-env-and-startup-properties

feat: implementation of support for host;port configuration from env and jar startup properties

Author: sladkoff

README.md

@@ -40,14 +40,41 @@ See [Health Checks](#health-checks) for more information on how to build your ow
 
 ## Installation & Configuration
 
+#### Configuration Hierarchy
+
+The Prometheus metrics exporter plugin supports multiple configuration sources for the HTTP endpoint (host/port). The configuration is applied in the following order of priority:
+
+1. **Environment Variables:**
+  - `MINECRAFT_PROMETHEUS_EXPORTER_HOST`
+  - `MINECRAFT_PROMETHEUS_EXPORTER_PORT`  
+    If these environment variables are set, their values will override all other settings.
+
+2. **System Properties:**
+  - `minecraft.prometheus.exporter.host`
+  - `minecraft.prometheus.exporter.port`  
+    If the environment variables are not provided, the plugin checks these system properties. They can be set when launching the JVM.
+
+3. **Configuration File:**  
+   If neither environment variables nor system properties are defined, the plugin falls back to the values in the configuration file.
+
+
 ### Plugin config
 
 The default configuration file will be created after the first use of the plugin.
 
 ```yml
 # Note that the HTTP server binds to localhost by default.
-# If your Prometheus runs on another host or inside a Kubernetes cluster
+# If your Prometheus runs on another host or inside a Kubernetes cluster,
 # set this to any reachable IP or 0.0.0.0 to listen on all interfaces.
+#
+# These settings can be overridden by environment variables or system properties.
+# Environment variables:
+#   - MINECRAFT_PROMETHEUS_EXPORTER_HOST: Overrides the host setting (e.g., 0.0.0.0)
+#   - MINECRAFT_PROMETHEUS_EXPORTER_PORT: Overrides the port setting (e.g., 9001)
+#
+# System properties (set during JVM startup):
+#   -Dminecraft.prometheus.exporter.host=0.0.0.0
+#   -Dminecraft.prometheus.exporter.port=9001
 host: localhost
 # The port can be changed in case it conflicts with any other application.
 port: 9940

src/main/kotlin/de/sldk/mc/PrometheusExporter.kt

@@ -25,9 +25,22 @@ class PrometheusExporter : JavaPlugin() {
         startMetricsServer(healthChecks)
     }
 
+    private fun getConfigValue(envKey: String, propertyKey: String, defaultValue: String): String {
+        return System.getenv(envKey) ?: System.getProperty(propertyKey) ?: defaultValue
+    }
+
     private fun startMetricsServer(healthChecks: HealthChecks) {
-        val host = config[PrometheusExporterConfig.HOST]
-        val port = config[PrometheusExporterConfig.PORT]
+        val host = getConfigValue(
+            envKey = "MINECRAFT_PROMETHEUS_EXPORTER_HOST",
+            propertyKey = "minecraft.prometheus.exporter.host",
+            defaultValue = config[PrometheusExporterConfig.HOST].toString()
+        )
+
+        val port = getConfigValue(
+            envKey = "MINECRAFT_PROMETHEUS_EXPORTER_PORT",
+            propertyKey = "minecraft.prometheus.exporter.port",
+            defaultValue = config[PrometheusExporterConfig.PORT].toString()
+        ).toInt()
 
         metricsServer = MetricsServer(host, port, this, healthChecks)