How to Deploy a Spring Boot App (Java & Kotlin) Without a Dockerfile

Spring Boot apps are usually deployed with a hand-written Dockerfile, a JVM base image and a lot of tuning. You can skip most of that: give the platform your Maven or Gradle project and it builds the JAR for you.

What happens on deploy#

1. pom.xml or build.gradle marks the project as Java/Kotlin.
2. Maven 3.9+ or Gradle 8.x builds an executable JAR.
3. The JAR runs on Eclipse Temurin, Java 17 or 21 LTS, with a tuned garbage collector.
4. You get https://<project>.dockhosting.cloud with automatic HTTPS.

Scheduled jobs (@Scheduled, Quartz) and background workers run alongside the web server.

1. Listen on the platform's port#

# src/main/resources/application.properties
server.port=${PORT:8080}
server.shutdown=graceful

${PORT:8080} uses the PORT variable in production and 8080 locally. Graceful shutdown lets in-flight requests finish during a zero-downtime deploy.

2. Add PostgreSQL#

Create a managed PostgreSQL database in the dashboard and attach it to the project. The spring.datasource properties are injected as environment variables, which Spring Boot maps onto its configuration automatically, so you don't hard-code a URL, user or password.

<!-- pom.xml -->
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
  <groupId>org.postgresql</groupId>
  <artifactId>postgresql</artifactId>
  <scope>runtime</scope>
</dependency>

For schema changes, use Flyway or Liquibase. Both run at startup, before the app takes traffic.

3. Fit the JVM into the container#

The JVM sizes its heap from the container's memory, but leaves little room for everything else. Set an explicit share:

JAVA_TOOL_OPTIONS=-XX:MaxRAMPercentage=75

Add it as an environment variable. Rough guide:

4. Deploy#

curl -fsSL https://cli.dockhosting.dev/install.sh | sh   # Windows: irm https://cli.dockhosting.dev/install.ps1 | iex
dock login
dock deploy

Follow the startup with dock logs. Spring Boot can take a while to start on a small container, so DockHosting gives apps up to 5 minutes to start listening before a start is marked as failed.

5. Faster startup#

• Trim starters you don't use. Each one adds auto-configuration work at boot.
• Lazy initialization (spring.main.lazy-initialization=true) defers beans until first use, at the cost of a slower first request.
• Expose a health endpoint with spring-boot-starter-actuator (/actuator/health) so you can tell "starting" from "broken".

Want full control of the image instead? Add a Dockerfile and it's built as-is. See deploying any Docker container.