diff --git a/spring-boot-project/spring-boot-actuator-autoconfigure/pom.xml b/spring-boot-project/spring-boot-actuator-autoconfigure/pom.xml index d7dd3b602d..cad5c3b02f 100644 --- a/spring-boot-project/spring-boot-actuator-autoconfigure/pom.xml +++ b/spring-boot-project/spring-boot-actuator-autoconfigure/pom.xml @@ -336,11 +336,6 @@ spring-integration-core true - - org.springframework.kafka - spring-kafka - true - org.springframework.security spring-security-config diff --git a/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/kafka/KafkaHealthIndicatorAutoConfiguration.java b/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/kafka/KafkaHealthIndicatorAutoConfiguration.java deleted file mode 100644 index 8bf093507f..0000000000 --- a/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/kafka/KafkaHealthIndicatorAutoConfiguration.java +++ /dev/null @@ -1,77 +0,0 @@ -/* - * Copyright 2012-2018 the original author or authors. - * - * 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.springframework.boot.actuate.autoconfigure.kafka; - -import java.time.Duration; -import java.util.Map; - -import org.springframework.boot.actuate.autoconfigure.health.CompositeHealthIndicatorConfiguration; -import org.springframework.boot.actuate.autoconfigure.health.ConditionalOnEnabledHealthIndicator; -import org.springframework.boot.actuate.autoconfigure.health.HealthIndicatorAutoConfiguration; -import org.springframework.boot.actuate.health.HealthIndicator; -import org.springframework.boot.actuate.kafka.KafkaHealthIndicator; -import org.springframework.boot.autoconfigure.AutoConfigureAfter; -import org.springframework.boot.autoconfigure.AutoConfigureBefore; -import org.springframework.boot.autoconfigure.EnableAutoConfiguration; -import org.springframework.boot.autoconfigure.condition.ConditionalOnBean; -import org.springframework.boot.autoconfigure.condition.ConditionalOnClass; -import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean; -import org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration; -import org.springframework.boot.context.properties.EnableConfigurationProperties; -import org.springframework.context.annotation.Bean; -import org.springframework.context.annotation.Configuration; -import org.springframework.kafka.core.KafkaAdmin; - -/** - * {@link EnableAutoConfiguration Auto-configuration} for {@link KafkaHealthIndicator}. - * - * @author Juan Rada - * @since 2.0.0 - */ -@Configuration -@ConditionalOnClass(KafkaAdmin.class) -@ConditionalOnBean(KafkaAdmin.class) -@ConditionalOnEnabledHealthIndicator("kafka") -@AutoConfigureBefore(HealthIndicatorAutoConfiguration.class) -@AutoConfigureAfter(KafkaAutoConfiguration.class) -@EnableConfigurationProperties(KafkaHealthIndicatorProperties.class) -public class KafkaHealthIndicatorAutoConfiguration - extends CompositeHealthIndicatorConfiguration { - - private final Map admins; - - private final KafkaHealthIndicatorProperties properties; - - public KafkaHealthIndicatorAutoConfiguration(Map admins, - KafkaHealthIndicatorProperties properties) { - this.admins = admins; - this.properties = properties; - } - - @Bean - @ConditionalOnMissingBean(name = "kafkaHealthIndicator") - public HealthIndicator kafkaHealthIndicator() { - return createHealthIndicator(this.admins); - } - - @Override - protected KafkaHealthIndicator createHealthIndicator(KafkaAdmin source) { - Duration responseTimeout = this.properties.getResponseTimeout(); - return new KafkaHealthIndicator(source, responseTimeout.toMillis()); - } - -} diff --git a/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/kafka/KafkaHealthIndicatorProperties.java b/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/kafka/KafkaHealthIndicatorProperties.java deleted file mode 100644 index fb156af68e..0000000000 --- a/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/kafka/KafkaHealthIndicatorProperties.java +++ /dev/null @@ -1,46 +0,0 @@ -/* - * Copyright 2012-2018 the original author or authors. - * - * 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.springframework.boot.actuate.autoconfigure.kafka; - -import java.time.Duration; - -import org.springframework.boot.actuate.kafka.KafkaHealthIndicator; -import org.springframework.boot.context.properties.ConfigurationProperties; - -/** - * Configuration properties for {@link KafkaHealthIndicator}. - * - * @author Juan Rada - * @since 2.0.0 - */ -@ConfigurationProperties(prefix = "management.health.kafka", ignoreUnknownFields = false) -public class KafkaHealthIndicatorProperties { - - /** - * Time to wait for a response from the cluster description operation. - */ - private Duration responseTimeout = Duration.ofMillis(1000); - - public Duration getResponseTimeout() { - return this.responseTimeout; - } - - public void setResponseTimeout(Duration responseTimeout) { - this.responseTimeout = responseTimeout; - } - -} diff --git a/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/kafka/package-info.java b/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/kafka/package-info.java deleted file mode 100644 index 35f3f26c68..0000000000 --- a/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/kafka/package-info.java +++ /dev/null @@ -1,20 +0,0 @@ -/* - * Copyright 2012-2018 the original author or authors. - * - * 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. - */ - -/** - * Auto-configuration for actuator Apache Kafka support. - */ -package org.springframework.boot.actuate.autoconfigure.kafka; diff --git a/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/resources/META-INF/additional-spring-configuration-metadata.json b/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/resources/META-INF/additional-spring-configuration-metadata.json index b23dde1645..5900250f65 100644 --- a/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/resources/META-INF/additional-spring-configuration-metadata.json +++ b/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/resources/META-INF/additional-spring-configuration-metadata.json @@ -107,12 +107,6 @@ "description": "Whether to enable JMS health check.", "defaultValue": true }, - { - "name": "management.health.kafka.enabled", - "type": "java.lang.Boolean", - "description": "Whether to enable Kafka health check.", - "defaultValue": true - }, { "name": "management.health.ldap.enabled", "type": "java.lang.Boolean", diff --git a/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/resources/META-INF/spring.factories b/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/resources/META-INF/spring.factories index 1cacddaa85..7ad0a7f5c0 100644 --- a/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/resources/META-INF/spring.factories +++ b/spring-boot-project/spring-boot-actuator-autoconfigure/src/main/resources/META-INF/spring.factories @@ -24,7 +24,6 @@ org.springframework.boot.actuate.autoconfigure.info.InfoEndpointAutoConfiguratio org.springframework.boot.actuate.autoconfigure.jdbc.DataSourceHealthIndicatorAutoConfiguration,\ org.springframework.boot.actuate.autoconfigure.jms.JmsHealthIndicatorAutoConfiguration,\ org.springframework.boot.actuate.autoconfigure.jolokia.JolokiaEndpointAutoConfiguration,\ -org.springframework.boot.actuate.autoconfigure.kafka.KafkaHealthIndicatorAutoConfiguration,\ org.springframework.boot.actuate.autoconfigure.ldap.LdapHealthIndicatorAutoConfiguration,\ org.springframework.boot.actuate.autoconfigure.liquibase.LiquibaseEndpointAutoConfiguration,\ org.springframework.boot.actuate.autoconfigure.logging.LogFileWebEndpointAutoConfiguration,\ diff --git a/spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/kafka/KafkaHealthIndicatorAutoConfigurationTests.java b/spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/kafka/KafkaHealthIndicatorAutoConfigurationTests.java deleted file mode 100644 index 20a5a5cb7a..0000000000 --- a/spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/kafka/KafkaHealthIndicatorAutoConfigurationTests.java +++ /dev/null @@ -1,57 +0,0 @@ -/* - * Copyright 2012-2018 the original author or authors. - * - * 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.springframework.boot.actuate.autoconfigure.kafka; - -import org.junit.Test; - -import org.springframework.boot.actuate.autoconfigure.health.HealthIndicatorAutoConfiguration; -import org.springframework.boot.actuate.health.ApplicationHealthIndicator; -import org.springframework.boot.actuate.kafka.KafkaHealthIndicator; -import org.springframework.boot.autoconfigure.AutoConfigurations; -import org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration; -import org.springframework.boot.test.context.runner.ApplicationContextRunner; - -import static org.assertj.core.api.Assertions.assertThat; - -/** - * Tests for {@link KafkaHealthIndicatorAutoConfiguration}. - * - * @author Juan Rada - */ -public class KafkaHealthIndicatorAutoConfigurationTests { - - private ApplicationContextRunner contextRunner = new ApplicationContextRunner() - .withConfiguration(AutoConfigurations.of(KafkaAutoConfiguration.class, - KafkaHealthIndicatorAutoConfiguration.class, - HealthIndicatorAutoConfiguration.class)); - - @Test - public void runShouldCreateIndicator() { - this.contextRunner.run( - (context) -> assertThat(context).hasSingleBean(KafkaHealthIndicator.class) - .doesNotHaveBean(ApplicationHealthIndicator.class)); - } - - @Test - public void runWhenDisabledShouldNotCreateIndicator() { - this.contextRunner.withPropertyValues("management.health.kafka.enabled:false") - .run((context) -> assertThat(context) - .doesNotHaveBean(KafkaHealthIndicator.class) - .hasSingleBean(ApplicationHealthIndicator.class)); - } - -} diff --git a/spring-boot-project/spring-boot-actuator/pom.xml b/spring-boot-project/spring-boot-actuator/pom.xml index 60644d6aa2..329876df51 100644 --- a/spring-boot-project/spring-boot-actuator/pom.xml +++ b/spring-boot-project/spring-boot-actuator/pom.xml @@ -235,11 +235,6 @@ spring-integration-core true - - org.springframework.kafka - spring-kafka - true - org.springframework.security spring-security-core @@ -277,21 +272,11 @@ spring-boot-autoconfigure test - - org.springframework.kafka - spring-kafka-test - test - org.apache.logging.log4j log4j-slf4j-impl test - - org.slf4j - log4j-over-slf4j - test - org.apache.logging.log4j log4j-api diff --git a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/kafka/KafkaHealthIndicator.java b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/kafka/KafkaHealthIndicator.java deleted file mode 100644 index 228a6de934..0000000000 --- a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/kafka/KafkaHealthIndicator.java +++ /dev/null @@ -1,87 +0,0 @@ -/* - * Copyright 2012-2018 the original author or authors. - * - * 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.springframework.boot.actuate.kafka; - -import java.util.Collections; -import java.util.Map; -import java.util.concurrent.ExecutionException; - -import org.apache.kafka.clients.admin.AdminClient; -import org.apache.kafka.clients.admin.Config; -import org.apache.kafka.clients.admin.DescribeClusterOptions; -import org.apache.kafka.clients.admin.DescribeClusterResult; -import org.apache.kafka.common.config.ConfigResource; -import org.apache.kafka.common.config.ConfigResource.Type; - -import org.springframework.boot.actuate.health.AbstractHealthIndicator; -import org.springframework.boot.actuate.health.Health.Builder; -import org.springframework.boot.actuate.health.HealthIndicator; -import org.springframework.boot.actuate.health.Status; -import org.springframework.kafka.core.KafkaAdmin; -import org.springframework.util.Assert; - -/** - * {@link HealthIndicator} for Kafka cluster. - * - * @author Juan Rada - * @since 2.0.0 - */ -public class KafkaHealthIndicator extends AbstractHealthIndicator { - - static final String REPLICATION_PROPERTY = "transaction.state.log.replication.factor"; - - private final KafkaAdmin kafkaAdmin; - - private final DescribeClusterOptions describeOptions; - - /** - * Create a new {@link KafkaHealthIndicator} instance. - * - * @param kafkaAdmin the kafka admin - * @param requestTimeout the request timeout in milliseconds - */ - public KafkaHealthIndicator(KafkaAdmin kafkaAdmin, long requestTimeout) { - Assert.notNull(kafkaAdmin, "KafkaAdmin must not be null"); - this.kafkaAdmin = kafkaAdmin; - this.describeOptions = new DescribeClusterOptions() - .timeoutMs((int) requestTimeout); - } - - @Override - protected void doHealthCheck(Builder builder) throws Exception { - try (AdminClient adminClient = AdminClient.create(this.kafkaAdmin.getConfig())) { - DescribeClusterResult result = adminClient - .describeCluster(this.describeOptions); - String brokerId = result.controller().get().idString(); - int replicationFactor = getReplicationFactor(brokerId, adminClient); - int nodes = result.nodes().get().size(); - Status status = nodes >= replicationFactor ? Status.UP : Status.DOWN; - builder.status(status).withDetail("clusterId", result.clusterId().get()) - .withDetail("brokerId", brokerId).withDetail("nodes", nodes); - } - } - - private int getReplicationFactor(String brokerId, AdminClient adminClient) - throws ExecutionException, InterruptedException { - ConfigResource configResource = new ConfigResource(Type.BROKER, brokerId); - Map kafkaConfig = adminClient - .describeConfigs(Collections.singletonList(configResource)).all().get(); - Config brokerConfig = kafkaConfig.get(configResource); - return Integer.parseInt(brokerConfig.get(REPLICATION_PROPERTY).value()); - } - -} diff --git a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/kafka/package-info.java b/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/kafka/package-info.java deleted file mode 100644 index 51978d8ac2..0000000000 --- a/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/kafka/package-info.java +++ /dev/null @@ -1,20 +0,0 @@ -/* - * Copyright 2012-2018 the original author or authors. - * - * 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. - */ - -/** - * Actuator support for Apache Kafka. - */ -package org.springframework.boot.actuate.kafka; diff --git a/spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/kafka/KafkaHealthIndicatorTests.java b/spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/kafka/KafkaHealthIndicatorTests.java deleted file mode 100644 index 595d8683b1..0000000000 --- a/spring-boot-project/spring-boot-actuator/src/test/java/org/springframework/boot/actuate/kafka/KafkaHealthIndicatorTests.java +++ /dev/null @@ -1,102 +0,0 @@ -/* - * Copyright 2012-2018 the original author or authors. - * - * 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.springframework.boot.actuate.kafka; - -import java.util.Collections; -import java.util.Map; - -import org.apache.kafka.clients.producer.ProducerConfig; -import org.junit.After; -import org.junit.Test; - -import org.springframework.boot.actuate.health.Health; -import org.springframework.boot.actuate.health.Status; -import org.springframework.kafka.core.KafkaAdmin; -import org.springframework.kafka.test.rule.KafkaEmbedded; -import org.springframework.util.SocketUtils; - -import static org.assertj.core.api.Assertions.assertThat; - -/** - * Tests for {@link KafkaHealthIndicator}. - * - * @author Juan Rada - * @author Stephane Nicoll - */ -public class KafkaHealthIndicatorTests { - - private KafkaEmbedded kafkaEmbedded; - - private KafkaAdmin kafkaAdmin; - - @After - public void shutdownKafka() throws Exception { - if (this.kafkaEmbedded != null) { - this.kafkaEmbedded.destroy(); - } - } - - @Test - public void kafkaIsUp() throws Exception { - startKafka(1); - KafkaHealthIndicator healthIndicator = new KafkaHealthIndicator(this.kafkaAdmin, - 1000L); - Health health = healthIndicator.health(); - assertThat(health.getStatus()).isEqualTo(Status.UP); - assertDetails(health.getDetails()); - } - - @Test - public void kafkaIsDown() { - int freePort = SocketUtils.findAvailableTcpPort(); - this.kafkaAdmin = new KafkaAdmin(Collections.singletonMap( - ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "127.0.0.1:" + freePort)); - KafkaHealthIndicator healthIndicator = new KafkaHealthIndicator(this.kafkaAdmin, - 1L); - Health health = healthIndicator.health(); - assertThat(health.getStatus()).isEqualTo(Status.DOWN); - assertThat((String) health.getDetails().get("error")).isNotEmpty(); - } - - @Test - public void notEnoughNodesForReplicationFactor() throws Exception { - startKafka(2); - KafkaHealthIndicator healthIndicator = new KafkaHealthIndicator(this.kafkaAdmin, - 1000L); - Health health = healthIndicator.health(); - assertThat(health.getStatus()).isEqualTo(Status.DOWN); - assertDetails(health.getDetails()); - } - - private void assertDetails(Map details) { - assertThat(details).containsEntry("brokerId", "0"); - assertThat(details).containsKey("clusterId"); - assertThat(details).containsEntry("nodes", 1); - } - - private void startKafka(int replicationFactor) throws Exception { - this.kafkaEmbedded = new KafkaEmbedded(1, true); - this.kafkaEmbedded.brokerProperties( - Collections.singletonMap(KafkaHealthIndicator.REPLICATION_PROPERTY, - String.valueOf(replicationFactor))); - this.kafkaEmbedded.before(); - this.kafkaAdmin = new KafkaAdmin( - Collections.singletonMap(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, - this.kafkaEmbedded.getBrokersAsString())); - } - -} diff --git a/spring-boot-project/spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc b/spring-boot-project/spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc index 9d419f04c2..fc6dae6e13 100644 --- a/spring-boot-project/spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc +++ b/spring-boot-project/spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc @@ -1272,8 +1272,6 @@ content into your application. Rather, pick only the properties that you need. management.health.elasticsearch.response-timeout=100ms # Time to wait for a response from the cluster. management.health.influxdb.enabled=true # Whether to enable InfluxDB health check. management.health.jms.enabled=true # Whether to enable JMS health check. - management.health.kafka.enabled=true # Whether to enable Kafka health check. - management.health.kafka.response-timeout=1000ms # Time to wait for a response from the cluster description operation. management.health.ldap.enabled=true # Whether to enable LDAP health check. management.health.mail.enabled=true # Whether to enable Mail health check. management.health.mongo.enabled=true # Whether to enable MongoDB health check. diff --git a/spring-boot-project/spring-boot-docs/src/main/asciidoc/production-ready-features.adoc b/spring-boot-project/spring-boot-docs/src/main/asciidoc/production-ready-features.adoc index cd1b820c61..7f5289b311 100644 --- a/spring-boot-project/spring-boot-docs/src/main/asciidoc/production-ready-features.adoc +++ b/spring-boot-project/spring-boot-docs/src/main/asciidoc/production-ready-features.adoc @@ -576,9 +576,6 @@ The following `HealthIndicators` are auto-configured by Spring Boot when appropr |{sc-spring-boot-actuator}/jms/JmsHealthIndicator.{sc-ext}[`JmsHealthIndicator`] |Checks that a JMS broker is up. -|{sc-spring-boot-actuator}/kafka/KafkaHealthIndicator.{sc-ext}[`KafkaHealthIndicator`] -|Checks that a Kafka server is up. - |{sc-spring-boot-actuator}/mail/MailHealthIndicator.{sc-ext}[`MailHealthIndicator`] |Checks that a mail server is up.