Compute Engine Java API

googlejavaapiThe usual way of managing Compute Engine instances is from GCP Console.  However, if you need programmatic access to Compute Engine, there is a comprehensive REST API. There are also client libraries (that basically wrap the REST API) provided by Google and the community, for Java, .NET, Go, JavaScript, Ruby and more.

In this post, I want to take a look at the Java client libraries. There are 2 client libraries for Java:

  1. Apache JClouds: This is an open source library that allows one to use Java across multiple Cloud providers, including Compute Engine on Google Cloud. This is a good option if you want to work with multiple cloud vendors from the same API.
  2. Google API Client Library for Java: Provided by Google, this is a Java library for accessing all Google APIs (not just Google Cloud), including Compute Engine on Google Cloud.

A good starting point to explore Google API Client Library for Java is Compute Engine Cmdline Sample. This sample basically contains a single class ComputeEngineSample that lists all compute engine instances you have in your project from Java. Nothing earth-shattering but it shows how to authenticate with Google API and interact with Compute Engine.

There’s an instructions.html file that tells you how to setup and use the sample. One thing you’ll realize is that you need to grant API access to your Java app before you can run the sample but instructions.html is a little outdated on that. This is what you need to do to grant API access:

  1. Either create or go to your project from Developer Console.
  2. Open side-menu on top left and go to “API Manager”.
  3.  Under “API Manager”, click on “Credentials” -> “Create Credentials” -> “OAuth Client ID”.
  4. Now, you need to select the application type. In our case, select “Other” and give it a name.
  5. At this point, you’ll have a pop-up with client ID and secret. Copy these down as you’ll need them later.

Once that’s done, you can import the project into Eclipse (or your favorite IDE), fill client_secrets.json in resources folder with client ID and secret from step 5, and fill the following info in ComputeEngineSample:

  • APPLICATION_NAME: Optional but give it a name, so you don’t get warnings.

  • projectId: Your project id from Developers Console.

  • zoneName: Make sure to enter the right zone for your project. In my case, I chose europe-west1-c.

That’s it. Now, you can run ComputeEngineSample from Eclipse (or your favorite IDE) and you can get info about your Compute Engine instances right from Java:

================== Listing Compute Engine Instances ==================
{
"canIpForward" : false,
"creationTimestamp" : "2016-02-16T05:58:00.714-08:00",
"description" : "",
"disks" : [ {
"autoDelete" : true,
"boot" : true,
"deviceName" : "instance-1",
"index" : 0,
"kind" : "compute#attachedDisk",
"mode" : "READ_WRITE",
    ....

 

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