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From Fang Wang <fang.w...@citrix.com>
Subject RE: [REVIEW/PROPOSAL/DISCUSS] API refactoring story: goal and notes
Date Thu, 20 Dec 2012 06:02:10 GMT
Prachi did an excellent FS document for this, and I added the high level goals section
To her FS link at wiki:

https://cwiki.apache.org/confluence/display/CLOUDSTACK/CloudStack+API+refactoring

Lots of implementation details are covered in the FS. We'll update it along the way. 
Thanks,
-Fang

-----Original Message-----
From: Fang Wang [mailto:fang.wang@citrix.com] 
Sent: Wednesday, December 19, 2012 9:46 PM
To: cloudstack-dev@incubator.apache.org
Subject: [REVIEW/PROPOSAL] API refactoring story: goal and notes

Hi all,
After answering questions about why/what we are doing to API refactoring, I'll add this to
the FS document.
Probably lots of people are not clear what is our motivation and what we want to achieve here.

(Will add this to the wiki page. )

The goal of the API refactoring
To make the system more modular and dynamic, API refactoring is part of the 4.1 new architecture
efforts. 
Another goal is to allow developers and partners to quickly add plugins and new service modules
and access control, making cloudstack more adaptive.
I am new on this as well In the beginning, I do not know too much about it. Now after working
on API refactoring, I got a better understanding of the existing problems and our solutions.
The solution is not the final perfect solution, for sure, feedback and suggestion is always
welcome to make it a much better and adaptive product. 

Current problem: 
1.	Security and access check is lying around in different layers. For example, in apiSevlet
we check the web access username/password credentials, apiServer checks the command existence,
and several other checks, then the DB access check mainly is done at the service layer. So
it is hard for developers and system admin to follow all the access and validations, to make
sure all the checks are done correctly. To do it, developers need to be familiar with the
various parts of the CS code. 

2.	Static: Majority of the DB access check and security validation is tightly coupled with
the lower layer service class. This not only made the code hard to follow, also inherently
made the policy static. This makes it impossible for system admin to apply a different security
policy adaptively. If one wants to adopt a different policy, not only he needs to understand
code scattered around, he also needs to rebuild the CS after any changes.  Any security role
modification is not dynamic.

3.	Performance implication: Access check done at the lower service layer makes the error code
path long. 

4.	Docs generated, CLI and APIs are loosely coupled.  

5.	Over the wire(OTW) entity is not well defined. For example, to listVMsCmd, it involves
multiple DB access, with the large amount of data showing NICs, Vols, Secondary storage etc,
the command can take quite a while. 

6.	Admin and user have basically the same end-point access. 

       The goal of the API refactoring is aiming to tackle these problems: 

1.	We would pull security checks, DB access checks, any related checks up from service layer/orchestration
engine to the API layer as much as possible. This makes the necessary checking done more centralized
and easy to follow. Conceptually the cloud orchestration engine layer handles the orchestration,
the security check and the access check should have done before reaching this layer. This
has performance benefits, since checks are done earlier instead of reaching deep in the code
path; this also has the benefits of a clear architecture. The API layer does the necessary
access check and role based authentication, makes it easier and dynamic for future policy
change. New policy can be added easily and dynamically as a plugin to the system. 

2.	The ACL and security checks also are written as adapter plugins, hence make them dynamic.
Users and developers and easily adapt new policy if needed. This made the code more modular
and more adaptive.

3.	Help improves performance: Instead of finding access error layer into the service layer,
by doing 1, we would do possible checks early in the code path, which helps stop the wrong
access earlier in the code path. 

4.	API layer is more tightly coupled with Doc generation, and CLI. Related commands are grouped
together, and the new @Doc annotation will help show the related commands in document. 

5.	We define new view objects as response objects, avoiding big DB joins at run time. 

6.	Separate the admin and user APIs. This is for developers to understand the code, which
should be accessible by users, which should only be handled by Admin.  Hence developers will
have better grasp of the role and pay attention to the new code added. It also helps the document
generated. 

       Notes:
1.	For end users, the new APIs after refactoring looks pretty much the same. One big change
is the ID, we will always use UUID in the over the wire APIs. The UUID can be created by Cloudstack,
or can be provided by users (we call it Xid - external ID). Every UUID should be unique in
the cloudstack system.

2.	The API layer provides a translation from the UUID to the internal DB_ID to the DB entity,
but this translation is done internally. Outside users will never see DB_ID. Before the response
is sending back by CS,  API layer replaces the internal DB_ID with the UUID. 

3.	In original FS document, the annotation of entityType in @Parameter points to a resource
class, this is replaced by a response class. So entityType points to a response object, and
the response class has a one-to-one mapping from the response to the physical entity itself.
This translation work is done by the API layer and the entityManagerImpl. 

4.	The packages for the new API commands are all moved from the current com.cloud.api.commands
to new location: org.apache.cloudstack.api.commands.user.[group name]
org.apache.cloudstack.api.commands.admin.[group_name]

The responses are also moved to new location at org.apache.cloudstack.api.response

More implementation details can refer to the FS document. We will also update the document
along the way. The code is branch from master at api_refactoring.  Since the change is not
minimum, we would like the community to know and give feedback.

Thanks,
-Fang

 

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