Category Archives: Development, Models and Methodologies

May 28

A pair of themes for ExtJS

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Reading time: 1 – 2 minutes

I’m a ExtJS JavaScript framework believer, but there other interesting and famous JavaScript frameworks like Bootstrap and jQuery. IMHO ExtJS is more focused on web applications than public web. In this post I want to share two ExtJS themes that helps to improve UI look and feel.

The first one is a bootstrap look and feel for ExtJS:

extjs-bootstrap

if you want to test it take a look to demo site. The theme is opensource and you can find the source in github.

The second and last one is Clifton theme.

clifton-theme

IMHO is a nice theme although it’s not really free. It costs around 320€, but in some professional projects it could be a really low price if you consider the effort to get a professional look and feel . You can try it in demo page.

Oct 11

Some recommendations about RESTful API design

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Reading time: 4 – 6 minutes

I want to recommend to you to watch the YouTube video called RESTful API design of Brian Mulloy. In this post I make an small abstract of the most important ideas of the video, of course from my point of view:

  • Use concrete plural nouns when you are defining resources.
  • Resource URL has to be focused in access collection of elements and specific element. Example:
    • /clients – get all clients
    • /clients/23 – get the client with ID 23
  • Map HTTP methods to maintein elements (CRUD):
    • POST – CREATE
    • GET – READ
    • PUT – UPDATE
    • DELETE – DELETE
  • Workaround, if your REST client doesn’t support HTTP methods, use a parameter called ‘method’ could be a good idea. For example, when you have to use a method HTTP PUT it could be changed by method HTTP GET and the parameter ‘method=put’ in the URL.
  • Sweep complexity behind the ’?’. Use URL parameters to filter or put some optional information to your request.
  • How to manage errors:
    • Use HTTP response codes to refer error codes. You can find a list of HTTP response codes  in Wikipedia.
    • JSON response example can be like this: 
      { 'message':'problem description', 'more_info':'http://api.domain.tld/errors/12345' }
    • Workaround, if REST client doesn’t know how to capture HTTP error codes and raise up an error losing the control of the client, you can use HTTP response code 200 and put ‘response_code’ field in JSON response object. It’s a good idea use this feature as optional across URL parameter ‘supress_response_code=true’.
  • Versioning the API. Use a literal ‘v’ followed by an integer number before the resource reference in the URL. It could be the most simple and powerful solution in this case. Example: /v1/clients/
  • The selection of what information will be returned in the response can be defined in the URL parameters, like in this example: /clients/23?fields=name,address,city
  • Pagination of the response. Use the parameters ‘limit’ and ‘offset’, keep simple. Example: ?limit=10&offset=0
  • Format of the answer, in this case I’m not completely agree with Brian. I prefer to use HTTP header ‘Accept’ than his proposal. Anyway both ideas are:
    • Use HTTP header ‘Accept’ with proper format request in the answer, for example, ‘Accept: application/json’ when you want a JSON response.
    • or, use extension ‘.json’ in URL request to get the response in JSON format.
  • Use Javascript format for date and time information, when you are formatting JSON objects.
  • Sometimes APIs need to share actions. Then we can’t define an action with a noun, in this case use verb. Is common to need actions like: convert, translate, calculate, etc.
  • Searching, there are two cases:
    • Search inside a resource, in this case use parameters to apply filters.
    • Search across multiple resource, here is useful to create the resource ‘search’.
  • Count elements inside a resource, simply add ‘/count’ after the resource. Example: /clients/count
  • As far as you can use a single base URL for all API resources, something like this: ‘http://api.domain.tld’.
  • Authentication, simply use OAuth 2.0
  • To keep your API KISS usually it’s a good idea develop SDK in several languages, where you can put more high level features than in API.
  • Inside an application each resource has its own API but it’s not a good idea publish it to the world, maybe use a virtual API in a layer above it’s more secure and powerful.

 

Mar 15

What is AMQP? and the architecture

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This entry is part 2 of 3 in the series AMQP and RabbitMQ

Reading time: 3 – 4 minutes

What is AMQP? (Advanced Message Queuing Protocol)

When two applications need to communicate there are a lot of solutions like IPC, if these applications are remote we can use RPC. When two or more applications communicate with each other we can use ESB. And there are many more solutions. But when more than two applications communicate and the systems need to be scalable the problem is a bit more complicated. In fact, when we need to send a call to a remote process or distribute object processing among different servers we start to think about queues.

Typical examples are rendering farms, massive mail sending, publish/subscriptions solutions like news systems. At that time we start to consider a queue-based solution. In my case the first approach to these types of solutions was Gearman; that is a very simple queue system where workers connect to a central service where producers have to call the methods published by workers; the messages are queued and delivered to workers in a simple queue.

Another interesting solution can be use Redis like a queue service using their features like publish/subscribe. Anyway always you can develop your own queue system. Maybe there a lot of solutions like that but when you are interested in develop in standard way and want a long-run solution with scalability and high availability then you need to think in use AMQP-based solutions.

The most simple definition of AMQP is: “message-oriented middleware”. Behind this simple definition there are a lot of features available. Before AMQP there was some message-oriented middlewares, for example, JMS. But AMQP is the standard protocol to keep when you choice a queue-based solution.

AMQP have features like queuing, routing, reliability and security. And most of the implementations of AMQP have a really scalable architectures and high availability solutions.

The architecture

The basic architecture is simple, there are a client applications called producers that create messages and deliver it to a AMQP server also called broker. Inside the broker the messages are routed and filtered until arrive to queues where another applications called consumers are connected and get the messages to be processed.

When we have understood this maybe is the time to deep inside the broker where there are AMQP magic. The broker has three parts:

  1. Exchange: where the producer applications delivers the messages,  messages have a routing key and exchange uses it to route messages.
  2. Queues: where messages are stored and then consumers get the messages from queues.
  3. Bindings: makes relations between exchanges and queues.

When exchange have a message uses their routing key and three different exchange methods to choose where the message goes:

    1. Direct Exchange:  routing key matches the queue name.
    2. Fanout Exchange: the message is cloned and sent to all queues connected to this exchange.
    3. Topic Exchange: using wildcards the message can be routed to some of connected queues.

This is the internal schema of a broker:

Mar 09

AMQP and RabbitMQ [TOC]

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This entry is part 1 of 3 in the series AMQP and RabbitMQ

Reading time: 1 – 2 minutes

After reading the book ‘RabbitMQ in action‘ I’m working on series of posts  that will include the following subjects:

  1. What is AMQP? and the architecure
  2. Deep inside AMQP
  3. RabbitMQ CLI quick reference
  4. Hello World using ‘kombu’ library and python
  5. Parallel programming
  6. Events example
  7. RPC
  8. Clustering fundamentals
  9. Managing RabbitMQ from administration web interface
  10. Managing RabbitMQ from REST API

Please let me know if you are interested in this series of posts. Because in my opinion this is very interesting and it always comes in handy to know if someone has been working on those subjects.