cdk.json

{
  "app": "${PROJECT_HOME}/gradlew -q run ${GRADLE_OFFLINE_OPTION}",
  "output": "build/cdk.out"
}

npxFromGradle.kts

fun commonCDKEnvironment(): Map<String, String> {
    return mapOf(
            "PROJECT_HOME" to project.rootDir.absolutePath,
            "SUB_PROJECT_HOME" to project.projectDir.absolutePath,
            "GRADLE_OFFLINE_OPTION" to if (project.gradle.startParameter.isOffline) "--offline" else ""
    )
}

tasks.register("synthCDK", NpxTask::class) {
    command = "aws-cdk@${cdkVersion}"

    args = listOf("synth")
    environment = commonCDKEnvironment()
    enabled = file("cdk.json").exists()
}