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Building a Dropwizard project
This blog post describes how to use Snap to deploy your Dropwizard services to Heroku with deployment pipelines.
Sahil Muthoo
snap ci, continuous delivery, continuous integration, developer tools, github, heroku, dropwizard, deployment pipelines,
java deployments

Dropwizard is a popular choice for deploying performant RESTful web services on the JVM platform. This blog post describes how to use Snap to deploy your Dropwizard services to Heroku with deployment pipelines.

Meet the sample Dropwizard service

For the purpose of this post I have created a sample Dropwizard service called dropwizard-snapci-sample. It's a simple microblogging service API with two resources, User and MicroBlog. It speaks to PostgreSQL using the light jdbi library with Liquibase database migrations. The sample service is testing using both unit tests and end to end integration tests.

To get started, fork this repository to your GitHub account.

The first stage of our deployment pipeline - running unit tests and packaging the service

When you setup a build for this repository, Snap will detect that it is a Maven project and create a single stage pipeline for you with an empty mvn command. Simply replace mvn with mvn package to run the unit tests and create a deployable microblog jar.

We're almost done with our first stage. Only exporting the build artifacts remain. See the documentation on [configuring and downloading artifacts]({{ }}artifacts/build_artifacts/#configuring-and-downloading-artifacts) for information on how to do this and why it's important. You'll want the target directory as an artifact for subsequent stages.

The stage task list should look like this:

with artifacts configured as follows

The second stage - end to end integration tests

We now need to ensure that the service works with a real database and web server. Our unit tests mock out database calls and we had no need to connect to a database server. However our integration tests require a database. Thus we need to tweak our service to connect to the PostgreSQL service that Snap provides your build.

Snap follows the Heroku convention of injecting an environment variable named DATABASE_URL into each stage's execution environment. We recommend checking out the Heroku dev center article Connecting to Relational Databases on Heroku with Java. In short- the DATABASE_URL is formatted like this [database type]://[username]:[password]@[host]:[port]/[database name].

Our sample service is already setup to use the DATABASE_URL environment variable. The code to do this is located in Here's what that code looks like:

URI dbUri = new URI(databaseUrl);
String user = dbUri.getUserInfo().split(":")[0];
String password = dbUri.getUserInfo().split(":")[1];
String url = "jdbc:postgresql://" + dbUri.getHost() + ':' + dbUri.getPort() + dbUri.getPath();
databaseConfiguration = new DatabaseConfiguration();

Once we have that, we can configure a stage in Snap as follows:

  • Select PostgreSQL from the database dropdown.
  • Create a new stage by clicking on Add new stage.
  • Select custom stage.
  • java -jar target/microblog-0.0.1-SNAPSHOT.jar db migrate microblog.yml runs the database migrations.
  • java -jar target/microblog-0.0.1-SNAPSHOT.jar server microblog.yml &>log & starts Jetty.
  • mvn failsafe:integration-test failsafe:verify runs our integration tests.

The target directory already contains our build artifact which was propagated by Snap from the previous stage.

Your integration stage should look something like this

The final stage - deploying to Heroku

Deploying to Heroku is the easiest part. First we need to ensure is that the web task in the Procfile runs our database migrations and starts up Jetty. You can see how to do this the Procfile of dropwizard-snapci-sample.

With the right Procfile we're ready to roll. Just add a new Heroku deployment stage and Snap takes care of the rest. If you need any help you can head over to the [Heroku deployments]({{ }}deployments/heroku_deployments/) section in our documentation.

Your Heroku deployment stage should look something like this

That's all there is to it. Snap will now monitor your repository and run builds for all commits. Snap has a lot more to offer from CCTray, HipChat and Campfire build notifications to manual gated deployments to production environments. Also, we're just getting warmed up. If there's a feature you'd like to see or if you just want to say hi feel free to [contact us]({{ }}).

Snap CI © 2017, ThoughtWorks

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