README.adoc

Immutable Configuration

The examples here demonstrate the Immutable Configuration Pattern which is uses an immutable configuration container linked to an application in one way or the other.

Demo application

For these examples we are using a simple "Hello World" type Java Servlet which picks up the configuration for a background color and a label from a properties file in the file system:

private Properties getConfig() throws IOException {
    Properties props = new Properties();
    props.load(new FileInputStream("/config/demo.properties"));
    return props;
}

You find the source to this example in the directory demo. Just run

mvn clean install

within this directory to re-create the war file. Binary copies of this application are already copied over to the example directories.

In order to test the application just call

mvn clean install tomcat7:run

and the direct your browser to http://localhost:8080/demo. You will get an error message that the configuration file can’t be found.

Examples

The following examples demonstrate how to apply the "Immutable Configuration" pattern to various enviroments:

• Docker Volumes demonstrates how to use plain Docker volumes to link together the configuration and application container.

• Init Container uses an init container initialize a pod’s volume with the configuration from a configuration container in a Kubernetes context.