Allow registration on multiple servers

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

@@ -196,7 +196,7 @@ The Spring Boot Admin Client registers the application at the admin server. This
 | `true`
 
 | spring.boot.admin.url
-| List of URLs of the Spring Boot Admin server to register at. This triggers the AutoConfiguration. *Mandatory*.
+| Comma separated ordered list of URLs of the Spring Boot Admin server to register at. This triggers the AutoConfiguration. *Mandatory*.
 |
 
 | spring.boot.admin.api-path
@@ -220,6 +220,10 @@ spring.boot.admin.password
 | Switch to enable auto-deregistration at Spring Boot Admin server when context is closed.
 | `false`
 
+| spring.boot.admin.register-once
+| If set to true the client will only register against one admin server (in order defined by `spring.boot.admin.url`); if that admin server goes down, will automatically register against the next admin server. If false, will register against all admin servers.
+| `true`
+
 | spring.boot.admin.client.health-url
 | Client-health-url to register with. Can be overridden in case the reachable URL is different (e.g. Docker). Must be unique in registry.
 | Guessed based on management-url and `endpoints.health.id`.

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

@@ -21,7 +21,7 @@ import org.springframework.boot.context.properties.ConfigurationProperties;
 public class AdminProperties {
 
 	/**
-	 * The admin servers url to register at
+	 * The admin server urls to register at
 	 */
 	private String[] url;
 
@@ -55,6 +55,11 @@ public class AdminProperties {
 	 */
 	private boolean autoRegistration = true;
 
+	/**
+	 * Enable registration against one or all admin servers
+	 */
+	private boolean registerOnce = true;
+
 	public void setUrl(String[] url) {
 		this.url = url.clone();
 	}
@@ -118,4 +123,12 @@ public class AdminProperties {
 	public void setAutoRegistration(boolean autoRegistration) {
 		this.autoRegistration = autoRegistration;
 	}
+
+	public boolean isRegisterOnce() {
+		return registerOnce;
+	}
+
+	public void setRegisterOnce(boolean registerOnce) {
+		this.registerOnce = registerOnce;
+	}
 }

spring-boot-admin-starter-client/src/main/java/de/codecentric/boot/admin/services/ApplicationRegistrator.java

@@ -41,7 +41,7 @@ public class ApplicationRegistrator {
 
 	private static HttpHeaders HTTP_HEADERS = createHttpHeaders();
 
-	private final AtomicReference<String> registeredId = new AtomicReference<String>();
+	private final AtomicReference<String> registeredId = new AtomicReference<>();
 
 	private AdminClientProperties client;
 
@@ -66,26 +66,28 @@ public class ApplicationRegistrator {
 	/**
 	 * Registers the client application at spring-boot-admin-server.
 	 *
-	 * @return true if successful
+	 * @return true if successful registration on at least one admin server
 	 */
 	public boolean register() {
+		boolean isRegistrationSuccessful = false;
 		Application self = createApplication();
-
 		for (String adminUrl : admin.getAdminUrl()) {
 			try {
 				@SuppressWarnings("rawtypes")
 				ResponseEntity<Map> response = template.postForEntity(adminUrl,
-						new HttpEntity<Application>(self, HTTP_HEADERS), Map.class);
+						new HttpEntity<>(self, HTTP_HEADERS), Map.class);
 
 				if (response.getStatusCode().equals(HttpStatus.CREATED)) {
-					if (registeredId.get() == null && registeredId.compareAndSet(null,
-							response.getBody().get("id").toString())) {
+					if (registeredId.compareAndSet(null, response.getBody().get("id").toString())) {
 						LOGGER.info("Application registered itself as {}", response.getBody());
-						return true;
+					} else {
+						LOGGER.debug("Application refreshed itself as {}", response.getBody());
 					}
 
-					LOGGER.debug("Application refreshed itself as {}", response.getBody());
-					return true;
+					isRegistrationSuccessful = true;
+					if (admin.isRegisterOnce()) {
+						break;
+					}
 				} else {
 					LOGGER.warn("Application failed to registered itself as {}. Response: {}", self,
 							response.toString());
@@ -96,7 +98,7 @@ public class ApplicationRegistrator {
 			}
 		}
 
-		return false;
+		return isRegistrationSuccessful;
 	}
 
 	public void deregister() {
@@ -105,8 +107,10 @@ public class ApplicationRegistrator {
 			for (String adminUrl : admin.getAdminUrl()) {
 				try {
 					template.delete(adminUrl + "/" + id);
-					registeredId.set(null);
-					return;
+					registeredId.compareAndSet(id, null);
+					if (admin.isRegisterOnce()) {
+						break;
+					}
 				} catch (Exception ex) {
 					LOGGER.warn(
 							"Failed to deregister application (id={}) at spring-boot-admin ({}): {}",

spring-boot-admin-starter-client/src/test/java/de/codecentric/boot/admin/services/ApplicationRegistratorTest.java

@@ -42,6 +42,7 @@ import de.codecentric.boot.admin.model.Application;
 
 public class ApplicationRegistratorTest {
 
+	private AdminProperties adminProps;
 	private ApplicationRegistrator registrator;
 	private RestTemplate restTemplate;
 	private HttpHeaders headers;
@@ -50,7 +51,7 @@ public class ApplicationRegistratorTest {
 	public void setup() {
 		restTemplate = mock(RestTemplate.class);
 
-		AdminProperties adminProps = new AdminProperties();
+		adminProps = new AdminProperties();
 		adminProps.setUrl(new String[] { "http://sba:8080", "http://sba2:8080" });
 
 		AdminClientProperties clientProps = new AdminClientProperties();
@@ -76,7 +77,7 @@ public class ApplicationRegistratorTest {
 		assertTrue(registrator.register());
 		verify(restTemplate)
 				.postForEntity("http://sba:8080/api/applications",
-						new HttpEntity<Application>(Application.create("AppName")
+						new HttpEntity<>(Application.create("AppName")
 								.withHealthUrl("http://localhost:8080/health")
 								.withManagementUrl("http://localhost:8080/mgmt")
 								.withServiceUrl("http://localhost:8080").build(), headers),
@@ -114,4 +115,72 @@ public class ApplicationRegistratorTest {
 
 		verify(restTemplate).delete("http://sba:8080/api/applications/-id-");
 	}
+
+	@SuppressWarnings("rawtypes")
+	@Test
+	public void register_multiple() {
+		adminProps.setRegisterOnce(false);
+
+		when(restTemplate.postForEntity(isA(String.class), isA(HttpEntity.class), eq(Map.class)))
+				.thenReturn(new ResponseEntity<Map>(Collections.singletonMap("id", "-id-"),
+						HttpStatus.CREATED));
+
+		assertTrue(registrator.register());
+
+		verify(restTemplate)
+				.postForEntity("http://sba:8080/api/applications",
+						new HttpEntity<>(Application.create("AppName")
+								.withHealthUrl("http://localhost:8080/health")
+								.withManagementUrl("http://localhost:8080/mgmt")
+								.withServiceUrl("http://localhost:8080").build(), headers),
+						Map.class);
+
+		verify(restTemplate)
+				.postForEntity("http://sba2:8080/api/applications",
+						new HttpEntity<>(Application.create("AppName")
+								.withHealthUrl("http://localhost:8080/health")
+								.withManagementUrl("http://localhost:8080/mgmt")
+								.withServiceUrl("http://localhost:8080").build(), headers),
+						Map.class);
+	}
+
+	@SuppressWarnings("rawtypes")
+	@Test
+	public void register_multiple_one_failure() {
+		adminProps.setRegisterOnce(false);
+
+		when(restTemplate.postForEntity(isA(String.class), isA(HttpEntity.class), eq(Map.class)))
+				.thenReturn(new ResponseEntity<Map>(Collections.singletonMap("id", "-id-"),
+						HttpStatus.CREATED))
+				.thenThrow(new RestClientException("Error"));
+
+		assertTrue(registrator.register());
+
+		verify(restTemplate)
+				.postForEntity("http://sba:8080/api/applications",
+						new HttpEntity<>(Application.create("AppName")
+								.withHealthUrl("http://localhost:8080/health")
+								.withManagementUrl("http://localhost:8080/mgmt")
+								.withServiceUrl("http://localhost:8080").build(), headers),
+						Map.class);
+
+		verify(restTemplate)
+				.postForEntity("http://sba2:8080/api/applications",
+						new HttpEntity<>(Application.create("AppName")
+								.withHealthUrl("http://localhost:8080/health")
+								.withManagementUrl("http://localhost:8080/mgmt")
+								.withServiceUrl("http://localhost:8080").build(), headers),
+						Map.class);
+	}
+
+	@Test
+	public void register_multiple_all_failures() {
+		adminProps.setRegisterOnce(false);
+
+		when(restTemplate.postForEntity(isA(String.class), isA(HttpEntity.class), eq(Map.class)))
+				.thenThrow(new RestClientException("Error"))
+				.thenThrow(new RestClientException("Error"));
+
+		assertFalse(registrator.register());
+	}
 }