Hello,

Here's the log:

2020-02-14 22:51:33.028  INFO 84 --- [  restartedMain] com.my.my.MyApplicationKt          : Starting MyApplicationKt on 476b89b0a321 with PID 84 (/var/www/build/classes/kotlin/main started by root in /var/www)
2020-02-14 22:51:33.052  INFO 84 --- [  restartedMain] com.my.my.MyApplicationKt          : No active profile set, falling back to default profiles: default
2020-02-14 22:51:33.124  INFO 84 --- [  restartedMain] o.s.b.devtools.restart.ChangeableUrls    : The Class-Path manifest attribute in /root/.gradle/caches/modules-2/files-2.1/io.grpc/grpc-netty-shaded/1.23.0/29c6b73d13098a7e0876cce325b3cd6204ed3297/grpc-netty-shaded-1.23.0.jar referenced one or more files that do not exist: file:/root/.gradle/caches/modules-2/files-2.1/io.grpc/grpc-netty-shaded/1.23.0/29c6b73d13098a7e0876cce325b3cd6204ed3297/grpc-core-1.23.0.jar,file:/root/.gradle/caches/modules-2/files-2.1/io.grpc/grpc-netty-shaded/1.23.0/29c6b73d13098a7e0876cce325b3cd6204ed3297/grpc-api-1.23.0.jar,file:/root/.gradle/caches/modules-2/files-2.1/io.grpc/grpc-netty-shaded/1.23.0/29c6b73d13098a7e0876cce325b3cd6204ed3297/gson-2.7.jar,file:/root/.gradle/caches/modules-2/files-2.1/io.grpc/grpc-netty-shaded/1.23.0/29c6b73d13098a7e0876cce325b3cd6204ed3297/annotations-4.1.1.4.jar,file:/root/.gradle/caches/modules-2/files-2.1/io.grpc/grpc-netty-shaded/1.23.0/29c6b73d13098a7e0876cce325b3cd6204ed3297/perfmark-api-0.17.0.jar,file:/root/.gradle/caches/modules-2/files-2.1/io.grpc/grpc-netty-shaded/1.23.0/29c6b73d13098a7e0876cce325b3cd6204ed3297/opencensus-contrib-grpc-metrics-0.21.0.jar,file:/root/.gradle/caches/modules-2/files-2.1/io.grpc/grpc-netty-shaded/1.23.0/29c6b73d13098a7e0876cce325b3cd6204ed3297/opencensus-api-0.21.0.jar,file:/root/.gradle/caches/modules-2/files-2.1/io.grpc/grpc-netty-shaded/1.23.0/29c6b73d13098a7e0876cce325b3cd6204ed3297/grpc-context-1.23.0.jar,file:/root/.gradle/caches/modules-2/files-2.1/io.grpc/grpc-netty-shaded/1.23.0/29c6b73d13098a7e0876cce325b3cd6204ed3297/error_prone_annotations-2.3.2.jar,file:/root/.gradle/caches/modules-2/files-2.1/io.grpc/grpc-netty-shaded/1.23.0/29c6b73d13098a7e0876cce325b3cd6204ed3297/jsr305-3.0.2.jar,file:/root/.gradle/caches/modules-2/files-2.1/io.grpc/grpc-netty-shaded/1.23.0/29c6b73d13098a7e0876cce325b3cd6204ed3297/animal-sniffer-annotations-1.17.jar,file:/root/.gradle/caches/modules-2/files-2.1/io.grpc/grpc-netty-shaded/1.23.0/29c6b73d13098a7e0876cce325b3cd6204ed3297/guava-26.0-android.jar,file:/root/.gradle/caches/modules-2/files-2.1/io.grpc/grpc-netty-shaded/1.23.0/29c6b73d13098a7e0876cce325b3cd6204ed3297/checker-compat-qual-2.5.2.jar,file:/root/.gradle/caches/modules-2/files-2.1/io.grpc/grpc-netty-shaded/1.23.0/29c6b73d13098a7e0876cce325b3cd6204ed3297/j2objc-annotations-1.1.jar
2020-02-14 22:51:33.128  INFO 84 --- [  restartedMain] .e.DevToolsPropertyDefaultsPostProcessor : For additional web related logging consider setting the 'logging.level.web' property to 'DEBUG'
...
2020-02-14 22:51:41.352  INFO 84 --- [  restartedMain] o.s.b.web.embedded.netty.NettyWebServer  : Netty started on port(s): 8080
2020-02-14 22:51:41.359  INFO 84 --- [  restartedMain] com.my.my.MyApplicationKt          : Started MyApplicationKt in 9.204 seconds (JVM running for 9.944)

probably this line indicates that DevTools works:

2020-02-14 22:51:33.128  INFO 84 --- [  restartedMain] .e.DevToolsPropertyDefaultsPostProcessor : For additional web related logging consider setting the 'logging.level.web' property to 'DEBUG'

but still, there's nothing else related to devtools and when I try to upload something, I get this:

Exception in thread "File Watcher" java.lang.IllegalStateException: Unexpected 404 NOT_FOUND response uploading class files

application.yml:

spring:
  devtools:
    remote:
      secret: ***
...

build.gradle.kts

import org.jetbrains.kotlin.gradle.tasks.KotlinCompile

plugins {
    id("org.springframework.boot") version "2.2.4.RELEASE"
    id("io.spring.dependency-management") version "1.0.9.RELEASE"
    kotlin("jvm") version "1.3.61"
    kotlin("plugin.spring") version "1.3.61"
    kotlin("kapt") version "1.3.61"
}

group = "com.my"
version = "0.0.1-SNAPSHOT"
java.sourceCompatibility = JavaVersion.VERSION_11

repositories {
    jcenter()
    mavenCentral()
}

val developmentOnly by configurations.creating
configurations {
    runtimeClasspath {
        extendsFrom(developmentOnly)
    }
}

dependencies {
    kapt("org.litote.kmongo:kmongo-annotation-processor:3.12.0")
    implementation("io.minio:minio:6.0.13")
    implementation("io.reactivex.rxjava3:rxjava:3.0.0-RC9")
    implementation("com.google.firebase:firebase-admin:6.12.1")
    implementation("org.litote.kmongo:kmongo-native:3.12.0")
    implementation("com.graphql-java:graphql-java-extended-scalars:1.0")
    implementation("com.expediagroup:graphql-kotlin-spring-server:2.0.0-RC6")
    implementation("org.springframework.boot:spring-boot-starter-security")
    implementation("org.springframework.boot:spring-boot-starter-data-mongodb")
    implementation("com.fasterxml.jackson.module:jackson-module-kotlin")
    implementation("org.jetbrains.kotlin:kotlin-reflect")
    implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8")
    developmentOnly("org.springframework.boot:spring-boot-devtools")
    testImplementation("org.springframework.boot:spring-boot-starter-test") {
        exclude(group = "org.junit.vintage", module = "junit-vintage-engine")
    }
}

// Add generated sources to your project source sets:
val check: DefaultTask by tasks

sourceSets {
    getByName("main").java.srcDirs("$buildDir/generated/source/app/main")
}

tasks.withType<Test> {
    useJUnitPlatform()
}

tasks.withType<KotlinCompile> {
    kotlinOptions {
        freeCompilerArgs = listOf("-Xjsr305=strict")
        jvmTarget = "1.8"
    }
}

I run the app with:

./gradlew bootRun

Comment From: wilkinsona

Remote DevTools is only supported with the Servlet-based stack at the moment. https://github.com/spring-projects/spring-boot/issues/13092 is tracking reactive support.