dgrid is a Java-based reliable queue and agent supporting jobs written in Java, Groovy, Javascript, or bash/perl/ruby/etc. dgrid also supports simple MapReduce jobs written in Java or Groovy. For additional info and more marketing-speak, see [http://www.structure28.com/dgrid/]http://www.structure28.com/dgrid/).

dgrid has a serverless mode, where jobs are stored in a relational database, and a client-server mode using a thrift-based protocol. TODO: write that server. "Transports" are designed to be pluggable, so an http/json transport or an Amazon AWS transport are likely next steps.

Jobs consist of one or more joblets. Joblets may be system executables (bash/perl/whatever), Java classes, Junit test cases, Groovy classes or Javascript. There are a number of provided joblets for things like uploading/downloading files to/from Amazon S3, sending SQS messages, sending email and sending xmpp messages. These are network-dependent and time consuming tasks that do not need to occur while responding to an http request. See the plugins/groovy/joblets directory for several samples.

Let's look at plugins/groovy/joblets/S3PutJoblet.groovy. First notice that it implements com.dgrid.api.SimpleJoblet, which Java-based joblets should implement as well. This interface defines one method:

public SimpleJobletResult execute(Joblet joblet, DGridClient gridClient) throws Exception;

Here's the implementation:

	// parameters are name/value pairs passed in
	Map<String, String> params = joblet.parameters;

	// this joblet requires four parameters and has two optional parameters
	String bucket = params.get("bucket");
	String key = params.get("key");
	String filename = params.get("file");

	// these are optional and assumed false by Boolean.parseBoolean() behavior
	boolean isPublic = Boolean.parseBoolean(params.get("public"));
	boolean deleteAfterPut = Boolean.parseBoolean(params.get("delete"));

	File file = new File(filename);

	// validate required params
	assert bucket != null, "Bucket may not be null";
	assert key != null, "Key may not be null";
	assert file.canRead(), "Cannot read file ${filename}";

	// use the S3Helper class to do actual work
	S3Helper s3 = (S3Helper) gridClient.getBean(S3Helper.NAME);
	String url = s3.put(file, bucket, key, isPublic);
	if (deleteAfterPut) {
		file.delete();
	}
	// return a result with 1) a return code to be used for anything you like,
	//  2) a status code indicating success or failure, and 3) a plain text
	//  field also to be used for anything (in this case a url for the file on S3.
	return new SimpleJobletResult(0, JOB_STATUS.COMPLETED, url);

We can insert this joblet into the system using dshell.jar:

java -jar dshell.jar --type groovy --param script:S3PutJoblet.groovy --param bucket:mybucket --param key:motd.txt --param file:/etc/motd --param public:true