Use InetAddress.getLocalHost() on prefer-ip

In case prefer-ip is true and no server.address is set use the IP address from
InetAddress.getLocalHost(); like it is done in Eureka.

spring-boot-admin-docs/src/main/asciidoc/index.adoc

@@ -228,7 +228,7 @@ spring.boot.admin.password
 | `${spring.application.name}` if set, `"spring-boot-application"` otherwise.
 
 | spring.boot.admin.client.prefer-ip
-| Use the ip-address rather then the hostname in the guessed urls. It's required to set `server.address` and `management.address`respectively.
+| Use the ip-address rather then the hostname in the guessed urls. If `server.address` / `management.address` is set they get used otherwise the IP address returned from `InetAddress.getLocalHost()` gets used.
 | `false`
 |===
 

spring-boot-admin-starter-client/src/main/java/de/codecentric/boot/admin/config/AdminClientProperties.java

@@ -25,12 +25,10 @@
 import org.springframework.boot.context.event.ApplicationReadyEvent;
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.context.event.EventListener;
-import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
 @ConfigurationProperties(prefix = "spring.boot.admin.client")
 public class AdminClientProperties {
-
 	/**
 	 * Client-management-URL to register with. Inferred at runtime, can be overriden in case the
 	 * reachable URL is different (e.g. Docker).
@@ -101,16 +99,17 @@ && getServiceUrl() != null) {
 		}
 
 		if (preferIp) {
-			Assert.notNull(management.getAddress(),
-					"management.address must be set when using preferIp");
-			return append(
-					append(createLocalUri(management.getAddress().getHostAddress(), managementPort),
-							server.getContextPath()),
-					management.getContextPath());
+			InetAddress address = management.getAddress();
+			if (address == null) {
+				address = getHostAddress();
+			}
+			return append(append(createLocalUri(address.getHostAddress(), managementPort),
+					server.getContextPath()), management.getContextPath());
 
 		}
 		return append(
-				append(createLocalUri(getHostname(), managementPort), server.getContextPath()),
+				append(createLocalUri(getHostAddress().getCanonicalHostName(), managementPort),
+						server.getContextPath()),
 				management.getContextPath());
 	}
 
@@ -140,12 +139,16 @@ public String getServiceUrl() {
 		}
 
 		if (preferIp) {
-			Assert.notNull(server.getAddress(), "server.address must be set when using preferIp");
-			return append(createLocalUri(server.getAddress().getHostAddress(), serverPort),
+			InetAddress address = server.getAddress();
+			if (address == null) {
+				address = getHostAddress();
+			}
+			return append(createLocalUri(address.getHostAddress(), serverPort),
 					server.getContextPath());
 
 		}
-		return append(createLocalUri(getHostname(), serverPort), server.getContextPath());
+		return append(createLocalUri(getHostAddress().getCanonicalHostName(), serverPort),
+				server.getContextPath());
 	}
 
 	public void setServiceUrl(String serviceUrl) {
@@ -187,9 +190,9 @@ private String append(String uri, String path) {
 		return baseUri + "/" + normPath;
 	}
 
-	private String getHostname() {
+	private InetAddress getHostAddress() {
 		try {
-			return InetAddress.getLocalHost().getCanonicalHostName();
+			return InetAddress.getLocalHost();
 		} catch (UnknownHostException ex) {
 			throw new IllegalArgumentException(ex.getMessage(), ex);
 		}

spring-boot-admin-starter-client/src/test/java/de/codecentric/boot/admin/config/AdminClientPropertiesTest.java

@@ -133,7 +133,7 @@ public void testSsl() {
 		assertThat(clientProperties.getServiceUrl(), is("https://" + getHostname() + ":8080"));
 	}
 
-	@Test(expected = IllegalArgumentException.class)
+	@Test
 	public void test_preferIpAddress_serveraddress_missing() {
 		load("local.server.port=8080");
 		AdminClientProperties clientProperties = new AdminClientProperties();
@@ -142,19 +142,20 @@ public void test_preferIpAddress_serveraddress_missing() {
 
 		publishApplicationReadyEvent(clientProperties);
 
-		clientProperties.getServiceUrl();
+		assertTrue(clientProperties.getServiceUrl()
+				.matches("http://\\d{0,3}\\.\\d{0,3}\\.\\d{0,3}\\.\\d{0,3}:8080"));
 	}
 
-	@Test(expected = IllegalArgumentException.class)
+	@Test
 	public void test_preferIpAddress_managementaddress_missing() {
 		load("local.server.port=8080", "local.management.port=8081");
 		AdminClientProperties clientProperties = new AdminClientProperties();
 		clientProperties.setPreferIp(true);
 		context.getAutowireCapableBeanFactory().autowireBean(clientProperties);
 
 		publishApplicationReadyEvent(clientProperties);
-
-		clientProperties.getManagementUrl();
+		assertTrue(clientProperties.getManagementUrl()
+				.matches("http://\\d{0,3}\\.\\d{0,3}\\.\\d{0,3}\\.\\d{0,3}:8081"));
 	}
 
 	@Test