Process Id Dealer

This project deals unique, sequential, reusable and contextual identifiers for processes running on a machine.

If you're running multiple instances of the same application and need to associate a small and reusable identifier, you've come to the right place.

Why not simply use pids? Because pids are too volatile for our use case.

Let's consider an example:

• The first, second and third instances get ids 0, 1 and 2, respectively.
• Now, if the second instance dies and another instance comes up, that new instance will be given id 1 since it was "freed" by the dying instance.
• If a different process type is run, it will be given id 0 as the process dealer is contextual.

This project was motivated by this StackOverflow question: http://stackoverflow.com/questions/23651327/sequential-and-contextual-process-identifier

The project is written in Node.js but can be used by any other language as it provides an HTTP server through wich the ids are dealt.

Running the server

Clone or download this project. Then run it as:

node server.js

The server can be configured. Have a look at the config.js file. You can change the config.js file directly but that is not recommended. All configuration options have associated environment variables which you can either define system-wide or just for the running session. So, to change the port at which the HTTP server listens, you could run:

PROCESS_ID_DEALER_SERVER_PORT=5000 node server.js

As the ids are dealt based on the original pids of the requesting applications and recycled when old pids die, it's necessary to run an instance of this server on each machine.

If the server dies or is restarted, the dealt ids are maintained since we're using LevelDB for storage.

Requesting an id

Using the default configuration, ids are dealt with the following request properties:

• Request type: GET
• Port: 4002
• Query parameters:
  • namespace: A string identifier of the requesting app. This allows multiple types of apps to have independently dealt ids.
  • id: The requesting process's pid.

Generic way

You can request an id by visiting the server's URL, for example:

http://localhost:4002/process-id/deal?namespace=com.example.app&pid=1234

And here's the corresponding cURL command:

curl -i -X GET "http://localhost:4002/process-id/deal?namespace=com.example.app&pid=1234"

The response is a JSON string as shown below. In this case, we were dealt id 0.

{"statusCode":200,"id":0}

From a Node.js app

This project also provides a client library for Node.js apps. You're welcome. The following code illustrates how you can request an id directly from your Node.js app.

First, install the npm module:

npm install process-id-dealer

Then, use it like this:

var dealerClient = require('process-id-dealer').client;

var options = {
  pid: process.pid,
  namespace: 'com.example.app',
  url: 'http://localhost:4002/process-id/deal',
  timeout: 10000  // Optional request timeout in ms. Default: 5000.
};

dealerClient.getId(options, function (err, id) {
  if (err) {
    // An error such as timeout or connection refused. Bad luck, junior.
    return;
  }
  // Successful request. `id` is the dealt identifer.
});