Apollo is a set of Java libraries that we use at Spotify when writing microservices. Apollo includes modules such as an HTTP server and a URI routing system, making it trivial to implement restful API services.

Apollo has been used in production at Spotify for a long time. As a part of the work to release version 1.0.0 we moved the development of Apollo into the open.

There are three main libraries in Apollo:

• apollo-http-service
• apollo-api
• apollo-core

If you need to solve a problem where the main APIs aren't powerful enough, apollo-environment provides more hooks, allowing you to modify the core behaviours of Apollo.

The apollo-http-service library is a standardized assembly of Apollo modules. It incorporates both apollo-api and apollo-core and ties them together with other modules to get a standard api service using http for incoming and outgoing communication.

The apollo-api library is the Apollo library you are most likely to interact with. It gives you the tools you need to define your service routes and your request/reply handlers.

Here, for example, we define that our service will respond to a GET request on the path / with the string "hello world":

public static void init(Environment environment) {
  environment.routingEngine()
      .registerAutoRoute(Route.sync("GET", "/", requestContext -> "hello world"));
}

The apollo-api library provides several ways to help you define your request/reply handlers. You can specify how responses should be serialized (such as JSON). Read more about this library in the Apollo API Readme.

The apollo-core library manages the lifecycle (loading, starting, and stopping) of your service. You do not usually need to interact directly with apollo-core; think of it merely as "plumbing". For more information about this library, see the Apollo Core Readme.

In addition to the three main Apollo libraries listed above, to help you write tests for your service we have an additional library called apollo-test. It has helpers to set up a service for testing, and to mock outgoing request responses.

Apollo will be distributed as a set of Maven artifacts, which makes it easy to get started no matter the build tool; Maven, Ant + Ivy or Gradle. Below is a very simple but functional service — more extensive examples are available in the examples directory. Until these are released, you can build and install Apollo from source by running mvn install.

public final class App {

    public static void main(String... args) throws LoadingException {
        HttpService.boot(App::init, "my-app", args);
    }

    static void init(Environment environment) {
        environment.routingEngine()
            .registerAutoRoute(Route.sync("GET", "/", rc -> "hello world"));
    }
 }

Metadata about an Apollo-based service, such as endpoints, is generated at runtime. At Spotify we use this to keep track of our running services. More info can be found here.

Examples from spotify-api-example:

$ curl http://localhost:8080/_meta/0/endpoints

{
  "result": {
    "docstring": null,
    "endpoints":[
      {
        "docstring": "Get the latest albums on Spotify.\n\nUses the public Spotify API https://api.spotify.com to get 'new' albums.",
        "method": [
          "GET"
        ],
        "methodName": "/albums/new[GET]",
        "queryParameters":[],
        "uri": "/albums/new"
      },
      {
        "docstring": "Responds with a 'pong!' if the service is up.\n\nUseful endpoint for doing health checks.",
        "method": [
          "GET"
        ],
        "methodName": "/ping[GET]",
        "queryParameters": [],
        "uri": "/ping"
      },
      ...
    ]
  }
}

$ curl http://localhost:8080/_meta/0/info

{
  "result": {
    "buildVersion": "spotify-api-example-service 1.3.1",
    "componentId": "spotify-api-example-service",
    "containerVersion": "apollo-http2.0.0-SNAPSHOT",
    "serviceUptime": 778.249,
    "systemVersion": "java 1.8.0_111"
  }
}

Introduction Website
JavaDocs
Maven site

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