Category Archives: Python

Microservice container with Guzzle

This days I’m reading about Microservices. The idea is great. Instead of building a monolithic script using one language/framowork. We create isolated services and we build our application using those services (speaking HTTP between services and application).

That’s means we’ll have several microservices and we need to use them, and maybe sometimes change one service with another one. In this post I want to build one small container to handle those microservices. Similar idea than Dependency Injection Containers.

As we’re going to speak HTTP, we need a HTTP client. We can build one using curl, but in PHP world we have Guzzle, a great HTTP client library. In fact Guzzle has something similar than the idea of this post: Guzzle services, but I want something more siple.

Imagine we have different services:
One Silex service (PHP + Silex)

use Silex\Application;

$app = new Application();

$app->get('/hello/{username}', function($username) {
    return "Hello {$username} from silex service";
});

$app->run();

Another PHP service. This one using Slim framework

use Slim\Slim;

$app = new Slim();

$app->get('/hello/:username', function ($username) {
    echo "Hello {$username} from slim service";
});

$app->run();

And finally one Python service using Flask framework

from flask import Flask, jsonify
app = Flask(__name__)

@app.route('/hello/<username>')
def show_user_profile(username):
    return "Hello %s from flask service" % username

if __name__ == "__main__":
    app.run(debug=True, host='0.0.0.0', port=5000)

Now, with our simple container we can use one service or another

use Symfony\Component\Config\FileLocator;
use MSIC\Loader\YamlFileLoader;
use MSIC\Container;

$container = new Container();

$ymlLoader = new YamlFileLoader($container, new FileLocator(__DIR__));
$ymlLoader->load('container.yml');

echo $container->getService('flaskServer')->get('/hello/Gonzalo')->getBody() . "\n";
echo $container->getService('silexServer')->get('/hello/Gonzalo')->getBody() . "\n";
echo $container->getService('slimServer')->get('/hello/Gonzalo')->getBody() . "\n";

And that’s all. You can see the project in my github account.

Sending sockets from PostgreSQL triggers with Python

Picture this: We want to notify to one external service each time that one record is inserted in the database. We can find the place where the insert statement is done and create a TCP client there, but: What happens if the application that inserts the data within the database is a legacy application?, or maybe it is too hard to do?. If your database is PostgreSQL it’s pretty straightforward. With the “default” procedural language of PostgreSQL (pgplsql) we cannot do it, but PostgreSQL allows us to use more procedural languages than plpgsql, for example Python. With plpython we can use sockets in the same way than we use it within Python scripts. It’s very simple. Let me show you how to do it.

First we need to create one plpython with our TCP client

CREATE OR REPLACE FUNCTION dummy.sendsocket(msg character varying, host character varying, port integer)
  RETURNS integer AS
$BODY$
  import _socket
  try:
    s = _socket.socket(_socket.AF_INET, _socket.SOCK_STREAM)
    s.connect((host, port))
    s.sendall(msg)
    s.close()
    return 1
  except:
    return 0
$BODY$
  LANGUAGE plpython VOLATILE
  COST 100;
ALTER FUNCTION dummy.sendsocket(character varying, character varying, integer)
  OWNER TO username;

Now we create the trigger that use our socket client.

CREATE OR REPLACE FUNCTION dummy.myTriggerToSendSockets()
RETURNS trigger AS
$BODY$
   import json
   stmt = plpy.prepare("select dummy.sendSocket($1, $2, $3)", ["text", "text", "int"])
   rv = plpy.execute(stmt, [json.dumps(TD), "host", 26200])
$BODY$
LANGUAGE plpython VOLATILE
COST 100;

As you can see in my example we are sending all the record as a JSON string in the socket body.

And finally we attach the trigger to one table (or maybe we need to do it to more than one table)

CREATE TRIGGER myTrigger
  AFTER INSERT OR UPDATE OR DELETE
  ON dummy.myTable
  FOR EACH ROW
  EXECUTE PROCEDURE dummy.myTriggerToSendSockets();

And that’s all. Now we can use one simple TCP socket server to handle those requests. Let me show you different examples of TCP servers with different languages. As we can see all are different implementations of Reactor pattern. We can use, for example:

node.js:

var net = require('net');

var host = 'localhost';
var port = 26200;

var server = net.createServer(function (socket) {
    socket.on('data', function(buffer) {
        // do whatever that we want with buffer
    });
});

server.listen(port, host);

python (with Twisted):

from twisted.internet import reactor, protocol

HOST = 'localhost'
PORT = 26200

class MyServer(protocol.Protocol):
    def dataReceived(self, data):
        # do whatever that we want with data
        pass

class MyServerFactory(protocol.Factory):
    def buildProtocol(self, addr):
        return MyServer()

reactor.listenTCP(PORT, MyServerFactory(), interface=HOST)
reactor.run()

(I know that we can create the Python’s TCP server without Twisted, but if don’t use it maybe someone will angry with me. Probably he is angry right now because I put the node.js example first :))

php (with react):

<?php
include __DIR__ . '/vendor/autoload.php';

$host = 'localhost';
$port = 26200;

$loop   = React\EventLoop\Factory::create();
$socket = new React\Socket\Server($loop);

$socket->on('connection', function ($conn) {
    $conn->on('data', function ($data) {
        // do whatever we want with data
        }
    );
});

$socket->listen($port, $host);
$loop->run();

You also can use xinet.d to handle the TCP inbound connections.

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