spring-boot docker docker-compose health-check paketo

Spring Boot Build Image with Health Check

I'm building my Docker image using Spring Boot's built in Gradle :bootBuildImage task, which is quite convenient, because I don't have to maintain my own Dockerfile.

The Gradle task uses the Paketo Bionic Base Stack under the hood and will build a layered Docker image just fine.

Now, some orchestration engines like Docker Swarm (or simply Docker Compose for dev purposes) execute health checks within the container. Unfortunately, however, the resulting Spring Boot Docker image doesn't have any health checker tools like curl or wget installed, so something like

version: '3.7'

services:
  springBootApp:
    image: my/springboot/docker-image
    healthcheck:
      test: ["CMD-SHELL", "curl http://localhost:8080/actuator/health"]

in docker-compose.yml will fail. (I checked that actuators themselves are working fine)

I know that curl or wget aren't ideal. I was actually hoping that the Paketo Builder would pick up something like this Health Checker BuildPack.

Is there a way to configure my bootBuildImage Gradle task to include that (or a similar) additional BuildPack?

As mentioned above, I'm looking for an easy to maintain solution and don't want to write my own Dockerfile to be able to profit from all the baked in best practices Paketo offers.

Solution

The Health Checkers buildpack hasn't been added to the main builders just yet, but it is fully available to use with your apps.

Instructions

Modify your build.gradle file:
```
tasks.named("bootBuildImage") {
  environment["BP_HEALTH_CHECKER_ENABLED"] = "true"
  buildpacks = ["urn:cnb:builder:paketo-buildpacks/java", "gcr.io/paketo-buildpacks/health-checker:latest"]
}
```
This will set an env variable at build time instructing the health-checkers buildpack to participate. It also tells Spring Boot build tools to append the health-checkers buildpack to the list of Java buildpacks that ship in the builder by default.

NOTE you may want to put in a particular version of health-checkers, that's up to you. It supports standard tag conventions like :1, :1.4, :1.4.0 and :latest so you can pin to latest major/minor or a specific version.

NOTE there is a breaking change in v2 of the health-checker buildpack see the release notes.

Build. ./gradlew bootBuildImage. You'll see the health checkers buildpack included in detection.

[creator]     ===> DETECTING
[creator]     7 of 27 buildpacks participating
[creator]     paketo-buildpacks/ca-certificates   3.6.0
[creator]     paketo-buildpacks/bellsoft-liberica 10.0.0
[creator]     paketo-buildpacks/syft              1.26.0
[creator]     paketo-buildpacks/executable-jar    6.6.2
[creator]     paketo-buildpacks/dist-zip          5.5.2
[creator]     paketo-buildpacks/spring-boot       5.23.0
[creator]     paketo-buildpacks/health-checker    1.3.1
...

Optional and for v1 of the health-checker buildpack only. Run pack inspect <image> against the produced image. You can see that health checkers has contributed a health-check process type. With v2 of the health-checker buildpack, it no longer contributes process types, because this caused issues.

Processes:
  TYPE                  SHELL        COMMAND        ARGS                                               WORK DIR
  web (default)                      java           org.springframework.boot.loader.JarLauncher        /workspace
  executable-jar                     java           org.springframework.boot.loader.JarLauncher        /workspace
  health-check                       thc                                                               /workspace
  task                               java           org.springframework.boot.loader.JarLauncher        /workspace

Run your app.
- For v1 of the health-checker buildpack, run docker run -d --health-cmd /cnb/process/health-check -p 8080:8080 -e THC_PATH=/actuator/health <image>.
- For v2 of the health-checker buildpack, run docker run -d --health-cmd /workspace/health-check -p 8080:8080 -e THC_PATH=/actuator/health <image>.
The health checker that's used by default is tiny-health-checker. It has other env variables you can configure but for a Spring Boot app you just need to set the actuator path (unless you have management port set differently, then set THC_PORT=<management-port> also.

If you are a Maven user, the process is very similar. Just substitute these instructions for step #1 and then #2 build with ./mvnw spring-boot:build-image.

    <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
        <configuration>
            <layers>
                <enabled>true</enabled>
            </layers>
            <image>
                <env>
                    <BP_HEALTH_CHECKER_ENABLED>true</BP_HEALTH_CHECKER_ENABLED>
                </env>
                <buildpacks>
                    <buildpack>urn:cnb:builder:paketo-buildpacks/java</buildpack>
                    <buildpack>gcr.io/paketo-buildpacks/health-checker:latest</buildpack>
                </buildpacks>
            </image>
        </configuration>
    </plugin>