Handle AbstractReactiveHealthIndicator.doHealthCheck exception

Exceptions inside AbstractReactiveHealthIndicator.doHealthCheck()
method, outside of Mono pipeline, could fail whole endpoint
response instead of returning `DOWN` status from indicator.

See gh-10822

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/AbstractReactiveHealthIndicator.java

@@ -29,8 +29,17 @@ public abstract class AbstractReactiveHealthIndicator implements ReactiveHealthI
 
 	@Override
 	public final Mono<Health> health() {
-		return doHealthCheck(new Health.Builder())
-				.onErrorResume((ex) -> Mono.just(new Health.Builder().down(ex).build()));
+		try {
+			return doHealthCheck(new Health.Builder())
+					.onErrorResume(this::handleFailure);
+		}
+		catch (Throwable ex) {
+			return handleFailure(ex);
+		}
+	}
+
+	private Mono<Health> handleFailure(Throwable ex) {
+		return Mono.just(new Health.Builder().down(ex).build());
 	}
 
 	/**

spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/redis/RedisReactiveHealthIndicatorTests.java

@@ -18,6 +18,7 @@ package org.springframework.boot.actuate.redis;
 
 import java.util.Properties;
 
+import io.lettuce.core.RedisConnectionException;
 import org.junit.Test;
 import reactor.core.publisher.Mono;
 import reactor.test.StepVerifier;
@@ -61,7 +62,7 @@ public class RedisReactiveHealthIndicatorTests {
 	}
 
 	@Test
-	public void redisIsDown() throws Exception {
+	public void redisCommandIsDown() throws Exception {
 		ReactiveServerCommands commands = mock(ReactiveServerCommands.class);
 		given(commands.info()).willReturn(
 				Mono.error(new RedisConnectionFailureException("Connection failed")));
@@ -75,6 +76,18 @@ public class RedisReactiveHealthIndicatorTests {
 		verify(redisConnection).close();
 	}
 
+	@Test
+	public void redisConnectionIsDown() throws Exception {
+		ReactiveRedisConnectionFactory redisConnectionFactory = mock(ReactiveRedisConnectionFactory.class);
+		given(redisConnectionFactory.getReactiveConnection()).willThrow(
+				new RedisConnectionException("Unable to connect to localhost:6379"));
+		RedisReactiveHealthIndicator healthIndicator = new RedisReactiveHealthIndicator(redisConnectionFactory);
+		Mono<Health> health = healthIndicator.health();
+		StepVerifier.create(health)
+				.consumeNextWith((h) -> assertThat(h.getStatus()).isEqualTo(Status.DOWN))
+				.verifyComplete();
+	}
+
 	private RedisReactiveHealthIndicator createHealthIndicator(
 			ReactiveRedisConnection redisConnection,
 			ReactiveServerCommands serverCommands) {