Run a Spring Boot app
In this guide we create and deploy a Spring Boot web server. To run this example, follow these steps:
-
Install the
kraft
CLI tool and a container runtime engine, e.g. Docker. -
Clone the
examples
repository andcd
into theexamples/java17-springboot3.2.x/
directory:
git clone https://github.com/kraftcloud/examplescd examples/java17-springboot3.2.x/
Make sure to log into Unikraft Cloud by setting your token and a metro close to you.
We use fra0
(Frankfurt, π©πͺ) in this guide:
# Set Unikraft Cloud access tokenexport UKC_TOKEN=token# Set metro to Frankfurt, DEexport UKC_METRO=fra0
When done, invoke the following command to deploy this application on Unikraft Cloud:
kraft cloud deploy -M 1024 -p 443:8080 .
The output shows the instance URL and other details:
[β] Deployed successfully! β βββββββββββ name: java17-springboot32x-qseeo βββββββββββ uuid: b081166d-a2a0-43af-982d-1aa17f06b5c4 ββββββββββ state: running ββββββββββββ url: https://long-dust-si7xsngk.fra0.kraft.host ββββββββββ image: java17-springboot32x@sha256:cc2f2ad18ce8e36b8e8f4debee096fef7b0bb8b47762575a2ba5a9de8199c64a ββββββ boot time: 153.97 ms βββββββββ memory: 1024 MiB ββββββββ service: long-dust-si7xsngk βββ private fqdn: java17-springboot32x-qseeo.internal βββββ private ip: 172.16.6.2 βββββββββββ args: /usr/lib/jvm/java-17-openjdk-amd64/bin/java -jar /usr/src/demo-0.0.1-SNAPSHOT.jar
In this case, the instance name is java17-springboot32x-qseeo
and the URL is https://long-dust-si7xsngk.fra0.kraft.host
.
They are different for each run.
Use curl
to querythe Spring Boot serverβs hello
endpoint:
curl https://long-dust-si7xsngk.fra0.kraft.host/hello
Hello World!
When done, you can remove the instance:
kraft cloud instance remove
Customize your Application
To customize the application, update the files in the repository, listed below:
DemoApplication.java
: the serverKraftfile
: the Unikraft Cloud specificationDockerfile
: the Docker-specified application filesystem
package com.example.demo;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.web.bind.annotation.GetMapping;import org.springframework.web.bind.annotation.RequestParam;import org.springframework.web.bind.annotation.RestController;
@SpringBootApplication@RestControllerpublic class DemoApplication {public static void main(String[] args) { SpringApplication.run(DemoApplication.class, args);}@GetMapping("/hello")public String hello(@RequestParam(value = "name", defaultValue = "World") String name) { return String.format("Hello %s!", name);}}
spec: v0.6
runtime: java:17
rootfs: ./Dockerfile
cmd: ["/usr/lib/jvm/java-17-openjdk-amd64/bin/java", "-jar", "/usr/src/demo-0.0.1-SNAPSHOT.jar"]
FROM --platform=linux/x86_64 debian:bookworm AS build
RUN set -xe ; \apt -yqq update ; \apt -yqq install default-jre default-jdk curl unzip ;
RUN ldconfig /usr/lib/jvm/java-17-openjdk-amd64/lib/
WORKDIR /src
RUN set -xe ; \curl -G https://start.spring.io/starter.zip \ -d applicationName=DemoApplication \ -d artifactId=demo \ -d bootVersion=3.2.2 \ -d dependencies=web \ -d description=com.example \ -d javaVersion=17 \ -d language=java \ -d name=demo \ -d packageName=com.example.demo \ -d packaging=jar \ -d type=maven-project \ -d version=0.0.1-SNAPSHOT \ -o demo.zip ; \unzip demo.zip \;
COPY DemoApplication.java src/main/java/com/example/demo/
RUN set -xe ; \./mvnw compile package install
RUN set -xe ; \mkdir /tmpdir
FROM scratch
COPY --from=build /tmpdir /tmpCOPY --from=build /src/target/demo-0.0.1-SNAPSHOT.jar /usr/src/demo-0.0.1-SNAPSHOT.jar
Lines in the Kraftfile
have the following roles:
-
spec: v0.6
: The currentKraftfile
specification version is0.6
. -
runtime: java:17
: The Unikraft runtime kernel to use is Java. -
rootfs: ./Dockerfile
: Build the application root filesystem using theDockerfile
. -
cmd: ["/usr/lib/jvm/java-17-openjdk-amd64/bin/java", "-jar", "/usr/src/demo-0.0.1-SNAPSHOT.jar"]
: Use as the starting command of the instance.
Lines in the Dockerfile
have the following roles:
-
FROM scratch
: Build the filesystem from thescratch
container image, to create a base image. -
COPY DemoApplication.java src/main/java/com/example/demo/
: Copy the server implementation file in the Docker filesystem.
The following options are available for customizing the application:
-
If only updating the implementation in the
DemoApplication.java
source file, no other change is required. -
If new files are added, these have to be copied in the application filesystem, using the
COPY
command in theDockerfile
. -
If a new Java source files is added, update the
cmd
line in theKraftfile
and replaceDemoApplication.java
to run that file when creating the instance. -
More extensive changes may require expanding the
Dockerfile
with additionalDockerfile
commands.
Learn More
Use the --help
option for detailed information on using Unikraft Cloud:
kraft cloud --help
Or visit the CLI Reference.