Introduce an AxonServer health indicator

Introduce an AxonServer health indicator by implementing the
AbstractHealthIndicator. It should add the connectivity of the existing
contexts within the AxonServerConnectionManager through the Health
.Builder

#1964

spring-boot-autoconfigure/pom.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!--
-  ~ Copyright (c) 2010-2021. Axon Framework
+  ~ Copyright (c) 2010-2022. Axon Framework
   ~
   ~ Licensed under the Apache License, Version 2.0 (the "License");
   ~ you may not use this file except in compliance with the License.
@@ -94,6 +94,13 @@
             <optional>true</optional>
         </dependency>
 
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-actuator</artifactId>
+            <version>${spring.boot.version}</version>
+            <optional>true</optional>
+        </dependency>
+
         <dependency>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-test</artifactId>

spring-boot-autoconfigure/src/main/java/org/axonframework/actuator/AxonServerHealthIndicator.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2010-2022. Axon Framework
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.axonframework.actuator;
+
+import org.axonframework.axonserver.connector.AxonServerConnectionManager;
+import org.springframework.boot.actuate.health.AbstractHealthIndicator;
+import org.springframework.boot.actuate.health.Health;
+
+/**
+ * An {@link AbstractHealthIndicator} implementation exposing the health of the connections made through the {@link
+ * AxonServerConnectionManager}. Shares information per connected context under {@code
+ * "{context-name}.connection.active"}.
+ *
+ * @author Steven van Beelen
+ * @since 4.6.0
+ */
+public class AxonServerHealthIndicator extends AbstractHealthIndicator {
+
+    private static final String CONNECTION = "%s.connection.active";
+
+    private final AxonServerConnectionManager connectionManager;
+
+    /**
+     * Constructs this health indicator, extracting health information from the given {@code connectionManager}.
+     *
+     * @param connectionManager The Axon Server CONNECTION manager to extract health information from.
+     */
+    public AxonServerHealthIndicator(AxonServerConnectionManager connectionManager) {
+        this.connectionManager = connectionManager;
+    }
+
+    @Override
+    protected void doHealthCheck(Health.Builder builder) {
+        connectionManager.connections()
+                         .forEach((key, value) -> builder.withDetail(String.format(CONNECTION, key), value));
+    }
+}