Cloud

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h2. Introduction

The purpose of this page is to gather the information related to using Qt in conjunction with Cloud computing. Some of the content and Qt framework development goals are the same as described in the Qt and Web Services wiki article but with the distinction that the Web Services article focuses more on interfacing most common existing Web Services (such as Facebook, Twitter, DropBox etc.). This page focus should be in using Cloud computing resources as the backend of existing Qt application or creating new Qt based services and applications that utilize for example Cloud storage.

Using Cloud Services from Qt applications

From the Qt application functionality point of view most interesting Cloud services are related to using Cloud hosted application back-ends or using cloud as the data storage. The Cloud services can be provided by specialized providers, or internally within the organization using the application – same principles and building blocks apply to both. Cloud Services are usually divided into Software as a Service (SaaS), Platform as a Service (PaaS) and Infrastructure as a Service (IaaS). Since Qt is not a web application development framework as such the focus is primarily on Platform and Infrastructure services. The Cloud services typically applicable for Qt based solutions include:

Platform (PaaS)

• Data storage (Blob, Table Storage and Relational Database Storage)
• Queue
• Identity and Access Management

Infrastructure (IaaS)

• Compute
• Network

Interfacing web applications such as Facebook, Twitter and LinkedIn from Qt application can be considered as SaaS type of access. Naming aside, also that level is important and the Cloud services need to allow this to be accomplished easily.

In cases where you have an existing Qt application that uses a relational database the easiest way to utilize Cloud storage is by using Relational Database Storage services. These services provide the database interface using the same mechanisms as databases usually provide remote access. Of course firewall and other security aspects must be taken into consideration.

If you already have a client-server based application implemented in Qt and want to use distributed and scalable computing environment, the most natural way is to use Virtualized Cloud Computing environment like Amazon EC2 or Azure Compute.

Many Cloud services expose REST API’s for managing and accessing the actual service. From Qt perspective REST based API’s are easier to use in a since Qt already includes almost all needed functionality. There are available Qt implementations also for accessing e.g. SOAP based services.

Cloud services per provider mapping

As an example of cloud service provider offering let’s investigate two popular cloud services Amazon AWS and Microsoft Azure.

|. |. Amazon|_. Azure|

| Data Storage - Blob | Simple Storage Service (S3), REST API | Blob storage REST API
| Data Storage - Table | SimpleDB, REST API | Azure Table Storage REST API
| Relational Database Storage| Relational Database Service (RDS), MySQL or Oracle DB, Getting Started Guide Azure SQL Storage, Microsoft SQL Server, Introducing SQL Azure Database
| Queue | Simple Queue Service, WSDL API | Windows Azure Queues, REST API |
| Identity & Access Management | AWS Identity and Access Management (IAM), WSDL API | Access Control Service (ACS), Several Access control features, See Overview of Access Control for details|
| Authentication in REST API’s | HMAC-SHA1 (deprecated) or HMAC-SHA256 based signature and AWS Access Key | HMAC-SHA256 based authorization header |

Requirements for Qt Framework development

Identified enhancements to existing modules

• JSON
  • Parsing through QScriptEngine already supported
  • Discussion about adding JSON support to QtCore module in qt-project development mailing list, and the initial patch has already been merged
  • JSON datamode for QML: QTBUG-12117
• Hash-based Message Authentication Code (HMAC)
  • HMAC- SHA256 needed for generating the authorization. QCryptographicHash should be extended to support SHA2 family (especially SHA256) QTBUG-2068 and there should be a way for creating the message authentication header QTBUG-904. Code snippet for HMAC-SHA1 in DevNet
• oAUTH
  • Discussion and planning ongoing. See status: QTBUG-6229

Qt SDK’s for different cloud services

Each of the Cloud services need a separate API implementation (often called as SDK’s). These provider specific API implementations can be the API’s that the application developer uses or those can be wrapped as plugins for generic Qt Cloud API or accessed through existing Qt Modules. At concept level for example QFile maps to Amazon S3 Objects and QDir maps to S3 Buckets, however for example the QFile is synchronous whereas Cloud Blob storage API should be asynchronous.

Generic Qt Cloud API

One possible approach would be creating a generic Qt Cloud API that would hide the Cloud service provider specific implementation. This approach would be similar to Simple Cloud API initiative.

Tools

• IDE Templates
• Sample Applications (Similar as QTBUG-13353)
• Documentation