Support config from system env in SentinelConfig and polish TransportConfig (#2154)

- An improved method for obtaining IP address and port number from containers

sentinel-core/src/main/java/com/alibaba/csp/sentinel/config/SentinelConfig.java

@@ -125,6 +125,24 @@ public final class SentinelConfig {
         AssertUtil.notNull(key, "key cannot be null");
         return props.get(key);
     }
+    
+    /**
+     * Get config value of the specific key.
+     *
+     * @param key config key
+     * @param envVariableKey Get the value of the environment variable with the given key
+     * @return the config value.
+     */
+    public static String getConfig(String key, boolean envVariableKey) {
+        AssertUtil.notNull(key, "key cannot be null");
+        if (envVariableKey) {
+            String value = System.getenv(key);
+            if (StringUtil.isNotEmpty(value)) {
+                return value;
+            }
+        }
+        return getConfig(key);
+    }
 
     public static void setConfig(String key, String value) {
         AssertUtil.notNull(key, "key cannot be null");

sentinel-transport/sentinel-transport-common/src/main/java/com/alibaba/csp/sentinel/transport/config/TransportConfig.java

@@ -140,7 +140,7 @@ public class TransportConfig {
         if (runtimePort > 0) {
             return String.valueOf(runtimePort);
         }
-        return SentinelConfig.getConfig(SERVER_PORT);
+        return SentinelConfig.getConfig(SERVER_PORT, true);
     }
 
     /**
@@ -159,7 +159,7 @@ public class TransportConfig {
      * @return the local ip.
      */
     public static String getHeartbeatClientIp() {
-        String ip = SentinelConfig.getConfig(HEARTBEAT_CLIENT_IP);
+        String ip = SentinelConfig.getConfig(HEARTBEAT_CLIENT_IP, true);
         if (StringUtil.isBlank(ip)) {
             ip = HostNameUtil.getIp();
         }