Building a Docker Image of your Micronaut application

Micronaut build plugins offer several ways to build Docker images - JAR, GraalVM native executable, CRaC

Authors: Sergio del Amo

Micronaut Version: 4.5.0

1. Getting Started

In this guide, we will create a Micronaut application written in Java.

2. What you will need

To complete this guide, you will need the following:

3. Solution

We recommend that you follow the instructions in the next sections and create the application step by step. However, you can go right to the completed example.

4. Writing the Application

Create an application using the Micronaut Command Line Interface or with Micronaut Launch.

mn create-app example.micronaut.micronautguide \
    --features=graalvm,crac,micronaut-aot \
    --build=maven \
    --lang=java \
If you don’t specify the --build argument, Gradle is used as the build tool.
If you don’t specify the --lang argument, Java is used as the language.
If you don’t specify the --test argument, JUnit is used for Java and Kotlin, and Spock is used for Groovy.

The previous command creates a Micronaut application with the default package example.micronaut in a directory named micronautguide.

If you use Micronaut Launch, select Micronaut Application as application type and add graalvm, crac, and micronaut-aot features.

If you have an existing Micronaut application and want to add the functionality described here, you can view the dependency and configuration changes from the specified features and apply those changes to your application.

5. Building a Docker Image with the Micronaut Maven Plugin

Micronaut Maven Plugin offers several options to package your application as a Docker Image.

  • docker builds a Docker image with the application artifacts (compiled classes, resources, dependencies, etc).

  • docker-native: builds a Docker image with a GraalVM native image inside.

  • docker-crac: build a a pre-warmed, checkpointed Docker Image

Moreover, you can combine AOT build optimizations with Docker packaging by including the system property micronaut.aot.enabled.

6. Controller

Add a controller which responds with the JSON payload in the root route.

{"message":"Hello World"}
package example.micronaut;

import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;

import java.util.Collections;
import java.util.Map;

@Controller (1)
public class HelloController {

    @Get (2)
    public Map<String, Object> index() {
        return Collections.singletonMap("message", "Hello World"); (3)
1 The class is defined as a controller with the @Controller annotation mapped to the path /.
2 The @Get annotation maps the method to an HTTP GET request.
3 The Micronaut framework will automatically convert it to JSON before sending it.

7. Time To First Request Measurement script

In this guide, we use the following script to measure time to first request of a Docker image.

#!/usr/bin/env bash

set -e


usage() {
  echo "$0: Time to first request for checkpoint, native, java or docker applications"
  echo ""
  echo "  $0 [-c|-d|-j|-n] [-p port] ARTIFACT"
  echo ""
  echo "    -c : ARTIFACT is a CRaC checkpoint"
  echo "    -d : ARTIFACT is a docker image (default)"
  echo "    -j : ARTIFACT is a fat jar"
  echo "    -n : ARTIFACT is a native executable"
  echo "    -p : port to check (default 8080)"
  echo ""

while getopts 'cdjnp:' flag; do
  case "${flag}" in
    c) TYPE="crac" ;;
    d) TYPE="docker" ;;
    j) TYPE="java" ;;
    n) TYPE="native" ;;
    p) PORT="${OPTARG}" ;;
    *) usage
       exit 1 ;;
shift $(($OPTIND - 1))
echo $1

if [ $# -eq 0 ]; then
  echo "Needs the docker image or Jar file to run"
  exit 1

execute() {
  local END=$((SECONDS+DELAY))
  while ! curl -o /dev/null -s "http://localhost:${PORT}"; do
    if [ $SECONDS -gt $END ]; then
      echo "No response from the app in $DELAY seconds" >&2
      exit 1
    sleep 0.001;

mytime() {
  exec 3>&1 4>&2
  mytime=$(TIMEFORMAT="%3R"; { time $1 1>&3 2>&4; } 2>&1)
  exec 3>&- 4>&-
  echo $mytime

if [[ "$TYPE" == "crac" ]]; then
  java -XX:CRaCRestoreFrom=$1 &
  TTFR=$(mytime execute)
  kill -9 $PID
elif [[ "$TYPE" == "java" ]]; then
  java -jar $1 &
  TTFR=$(mytime execute)
  kill -9 $PID
elif [[ "$TYPE" == "docker" ]]; then
  CONTAINER=$(docker run -d --rm -p $PORT:$PORT --privileged $1)
  TTFR=$(mytime execute)
  docker container kill $CONTAINER > /dev/null
  $1 &
  TTFR=$(mytime execute)
  kill -9 $PID

if [ "$TTFR" != "" ]; then
    echo "${TTFR} seconds"
    exit 1

7.1. Docker Image

Generate a Docker Image with:

./mvnw package -Dpackaging=docker
[INFO] Built image to Docker daemon as micronautguide
[INFO] Executing tasks:
[INFO] [==============================] 100.0% complete
[INFO] ------------------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  13.467 s
[INFO] Finished at: 2023-02-13T11:06:16+01:00

Supply to image name and tag to the time to first request script:

./ micronautguide:latest
2.473 seconds

7.2. Docker image with a GraalVM native executable inside

Generate a Docker Image with:

./mvnw package -Dpackaging=docker-native -Pgraalvm
[INFO] OK: 19 MiB in 18 packages
[INFO] Removing intermediate container 8779752a14f2
[INFO]  ---> ce1f4cc2a00e
[INFO] Step 14/17 : COPY --from=builder /home/app/application /app/application
[INFO]  ---> d6910584b917
[INFO] Step 15/17 : ARG PORT=8080
[INFO]  ---> Running in e18c65e28d66
[INFO] Removing intermediate container e18c65e28d66
[INFO]  ---> 3215839af33e
[INFO] Step 16/17 : EXPOSE ${PORT}
[INFO]  ---> Running in 7e3cb6cb6c60
[INFO] Removing intermediate container 7e3cb6cb6c60
[INFO]  ---> 8285031d9cf1
[INFO] Step 17/17 : ENTRYPOINT ["/app/application"]
[INFO]  ---> Running in 69ce96bc2a28
[INFO] Removing intermediate container 69ce96bc2a28
[INFO]  ---> cada15938fc4
[INFO] Successfully built cada15938fc4
[INFO] Successfully tagged micronautguide:latest
[INFO] ------------------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  01:58 min
[INFO] Finished at: 2023-02-13T11:11:10+01:00
[INFO] ------------------------------------------------------------------------

Run the time to first request script with the Native Docker Image:

./ micronautguide:latest

8. CRaC Docker Image

Generate a Docker Image containing a CRaC enabled JDK and a pre-warmed, checkpointed application:

./mvnw package -Dpackaging=docker-crac

Run the time to first request script with CRaC Docker Image:

./ micronautguide:latest
0.462 seconds

8.1. AOT Optimized Docker Image

./mvnw package -Dpackaging=docker -Dmicronaut.aot.enabled=true

Run the time to first request script with AOT optimized Docker Image:

./ micronautguide:latest
2,359 seconds

8.2. AOT Optimized Docker Image with a native executable inside

./mvnw package -Dpackaging=docker-native -Dmicronaut.aot.enabled=true -Pgraalvm

Run the time to first request script with AOT optimized Docker Image:

./ micronautguide:latest
0.039 seconds

9. Comparisons

Micronaut Framework offers many options for packaging your application as a Docker Image. As illustrated in the following chart, you can speed up your Docker Images by using the GraalVM integration in the Micronaut Framework, the CRaC (Coordinated Restore at checkpoint) integration in the Micronaut Framework, Micronaut AOT Gradle Plugin or Maven Plugin integration with Micronaut AOT.

The following chart illustrates the speed gains you can obtain:

docker image ttfr

Docker Image

2s 473ms

Optimized Docker Image

2s 359ms

CRaC Docker Image


Native Docker Image


Optimized Native Docker Image


I used the following hardware to calculate the previous benchmarks



Model Name

iMac Pro 2017


3GHz 10-Core Intel Xeon W


32 GB 2666 MHz DDR4

Total Number of Cores


Operating System

Mac OS X 10.15.7 (Mojave)

11. Help with the Micronaut Framework

The Micronaut Foundation sponsored the creation of this Guide. A variety of consulting and support services are available.

12. License

All guides are released with an Apache license 2.0 license for the code and a Creative Commons Attribution 4.0 license for the writing and media (images…​).