Build Simple SaaS with jclouds and Carina

Datetime:2016-08-23 03:52:15         Topic: Docker  Tomcat          Share        Original >>
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Traditionally, creating and monetizing an online software solution has been a difficult process. With Docker and Carina, it has become much easier to set up software as a service (SaaS) solutions online. This post provides an example of a Tomcat application that directly controls Carina by using the Docker API to instantly start up user-specific software services on demand.


You need the following set of tools to follow along.


The goal is to deploy an example Tomcat web application that can, on demand, provide a Mumble server to a user online. Mumble is a server/client VOIP telecommunication application.

Set up credentials

  1. Using Git, get the source code for the example application:

    $ git clone
  2. Log in to Carina.

  3. In the area for your cluster, click Get access and then download the access file.

  1. Extract the contents of the access file into the directory access within the repo that you cloned.

The example web application parses the extracted files to connect to your Carina account and to start and stop Mumble containers on demand.

Set up the project

This example project uses Maven to handle building, packaging, and dependencies, as defined in the pom.xml file.

  1. Set up the project name, version, and packaging:

  2. Because the code uses some bug fixes and features that have not been released, you need to include the Apache snapshot repository in the project:

          <name>Apache Development Snapshot Repository</name>
  3. Include the Tomcat servlet dependency, which enables the application to run on Tomcat as a servlet:

  4. Because the project uses Java and Java Server Pages, include the JSP Standard Tag Library to provide templates for displaying container data:

  5. Include Apache jclouds in the project. It is an open-source multi-cloud SDK that supports the Docker API (Carina uses the Docker API). Use the snapshot version of the jclouds dependency:

  6. To generate a cryptographically secure password, use a dependency that provides a secure random algorithm from Apache Commons:

  7. Enter the Maven build settings:

                <!-- Letting the application know we are running embedded -->

    The first plug-in enables building the project as a war package. The war package is an archive format that contains a Java application that Tomcat can run. The second plug-in allows you to run the project by using an embedded Tomcat server. Thus, you don't need to deploy the project and can run it locally for debugging purposes.


You define the servlet's mapping in the web.xml file. This mapping tells Tomcat how to route requests to the application. Routing is configured to use the ContainerController controller, which automatically redirects requests to the listcontainer.jsp page. This page lists all the available Mumble servers and provides a link to create a new Mumble container. When a new Mumble container is created by ContainerController, details about it are displayed in the newcontainer.jsp page. In the file, you can see how the different variables displayed in the JSP views are populated, and see all the logic needed to create, list, and delete Mumble containers.


Obtain a "connection" to the Docker API in the ContainerController constructor:

if("true".equals( System.getProperties().getProperty("cse.embeddedTomcat") )) {
   dockerApi = getDockerApiFromCarinaDirectory("access"); // From maven
} else {
   dockerApi = getDockerApiFromCarinaDirectory("/usr/local/access"); // From docker

If Tomcat is running embedded, you parse the local "access" directory. Otherwise, the credentials files are located on a Tomcat container, within the /usr/loca/access directory. That's right, you will be running and testing the Tomcat example application within a Docker container as well, and it will control other Docker containers. This example runs everything containerized.

The doGet method handles GET requests against the controller. The action that is executed is determined by the action get parameter:

String action = request.getParameter("action");

The variable forward determines which JSP view is used after the action is processed.

List existing containers

The default behavior (when no other action is specified) is to list all the existing Mumble containers.

request.setAttribute("containers", filter(dockerApi.getContainerApi().listContainers(), Utils.isMumble));

Utils.isMumble is a predicate that filters containers that have a name containing mumble . This also means that when the controller starts a new Mumble container, it has to include mumble in the name.

Delete a container

To delete a container, use the delete action and specfy a containerId value:

String containerId = request.getParameter("containerId");

Creat a new container

The create action is the most complex.

  1. Use Utils.getSecurePassword() to get a secure password using SecureRandom .

    String characters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
    return RandomStringUtils.random( 10, 0, 0, false, false, characters.toCharArray(), new SecureRandom() );
  2. Create and start the container:

    Container container = dockerApi.getContainerApi().createContainer("mumble" + UUID.randomUUID().toString(),
                                     "SERVER_TEXT=Welcome to My Mumble Server",
                                     "SUPW=" + password
    String id =;

The jclouds Docker API provides a createContainer method that accepts a name and a configuration object. The configuration object here specifies the Docker Hub container image extra/mumble , requires all service ports to be open, and configures Mumble server configuration options - such as maximum number of users, welcome text, and server administrator password - through environment variables. The createContainer method returns a Container object, which then the startContainer method starts.

The ContainerController then populates the view variables for ports and password and redirects to the page responsible for displaying new containers.

Run the application locally

Use the following code to run the application locally, without deploying to a Tomcat container:

$ mvn clean tomcat7:run-war

To run in debug mode, use mvndebug instead of mvn .

Deploy the Tomcat application to Docker

The project includes a DOCKERFILE that creates a custom image based on the official Docker Hub Tomcat 8 image. The following additional files are added:

  • cse.war , the archived application; The file is available after a Maven build has been executed.
  • docker.ps1 , cert.pem , key.pem . These files are used for authentication to Carina and are placed in the access directory during project setup.

To build the custom image, run the following command:

$ docker build -t cse .

After the custom image is ready, deploy it to Carina (you need to have Docker configured to connect to Carina):

$ docker run --name cse -d -p 8080:8080 cse

This uses port 8080 for the Tomcat application server. Connect to http://[address]:8080/cse to view the example application's List Containers page.

Listing Mumble containers from the application:

A new Mumble server:


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