Moving a Java application to Upsun

It is common to have a Java application that you want to migrate to Upsun. Upsun supports several styles of Java application, such as monolith, microservices, stateful, and stateless.

Minimum Requirement

To run a Java application at Upsun you need:

• A supported Java version
• A build management tool
  • Gradle
  • Maven
  • Maven Wrapper
  • Ant
• A Git Repository:
  • GitHub
  • BitBucket
  • GitLab
  • The default Git repository provided by Upsun

Monolith/Single Application

To start a Java application, you need to understand the Upsun structure. You will need to configure your application, routes, and services.

Application

applications:
    app:
        type: 'java:<VERSION>'

        hooks:
            build: [2]
        web:
            commands:
                start: [3]

1. A Java version, e,g.: java:21
2. Hooks define what happens when building the application. This build process typically generates an executable file such as a uber-jar e.g.: mvn clean package
3. The commands key defines the command to launch the application. E.g.: java -jar file.jar
4. In the start’s command needs to receive the port where the application will execute thought the PORT environment. That’s best when your app follows the port bind principle. E.g.: java -jar jar --port=$PORT

Route

routes:
    "https://{default}/":
        type: upstream
        upstream: "app:http" [1]
    "https://www.{default}/":
        type: redirect
        to: "https://{default}/"

applications:
    app:
        type: 'java:<VERSION>'

        hooks:
            build: [2]
        web:
            commands:
                start: [3]

1. It defines the application will link in the route, e.g.: "app:http"

Microservices

You have the option to use several languages in microservices. If you’re using Java there are several options to aggregate these services into a microservices:

• Maven Modules
• Gradle Multi-project
• Git submodules

Upsun supports multiple applications and there are two options:

• One application YAML file to each application
• Aggregate all applications in a single file with an .upsun/config.yaml file

Access to managed services

Upsun provides managed services such as databases, cache and search engines. However, you can use a database or any services such as a transition process, just be aware of the firewall.

When applications need to access a service, it is important to include the relationships key. By default an application may not talk to any other container without a relationship explicitly allowing access.

To connect to a service from your deployed application, you need to pass the relationships information into your application’s configuration. The way to do so varies with the application. The most common mechanisms are listed below.

Overwrite

If you are using a framework that follows the Twelve-Factor App methodology, particularly the third point, you can configure the application directly from environment variables. Examples of such frameworks include Spring, Eclipse MicroProfile Config, Quarkus, and Micronauts.

Service credentials are available within the PLATFORM_RELATIONSHIPS environment variable. This variable is a base64-encoded JSON object with keys of the relationship name and values of arrays of relationship endpoint definitions.

Upsun supports the jq tool, which allows to extract information from this JSON.

export DB_HOST=`echo $PLATFORM_RELATIONSHIPS | base64 --decode | jq -r ".database[0].host"`

To reduce the number of lines in the application file and to make it cleaner, you have the option to move the variable environment to another file: a .environment file.

E.g.:

export DB_HOST=`echo $PLATFORM_RELATIONSHIPS | base64 --decode | jq -r ".database[0].host"`
export DB_PASSWORD=`echo $PLATFORM_RELATIONSHIPS | base64 --decode | jq -r ".database[0].password"`
export DB_USER=`echo $PLATFORM_RELATIONSHIPS | base64 --decode | jq -r ".database[0].username"`
export DB_DATABASE=`echo $PLATFORM_RELATIONSHIPS | base64 --decode | jq -r ".database[0].path"`
export JDBC=jdbc:postgresql://${HOST}/${DATABASE}
export JAVA_MEMORY=-Xmx$(jq .info.limits.memory /run/config.json)m
export JAVA_OPTS="$JAVA_MEMORY -XX:+ExitOnOutOfMemoryError"

This .environment can interact to each application file. E.g.:

applications:
    # The app's name, which must be unique within the project.
    app:
        type: 'java:21'
        hooks:
            build: ./mvnw package -DskipTests -Dquarkus.package.uber-jar=true
        relationships:
            database: "db:postgresql"
        web:
            commands:
                start: java -jar $JAVA_OPTS $CREDENTIAL -Dquarkus.http.port=$PORT jarfile.jar