MSDN Utopia : Services

Design: Architecture Frame Considerations (Part 2)

Salva Patuel — Tue, 10 Feb 2009 19:58:00 GMT

In this second instalment we are going to review another set of frames. This guideline should help you to understand what is involved on each one of them as well as considerations and known patterns.

You can find the first part following this link.

The second part looks like this:

The following guideline can help you to identify the key issues on each area of the frame and some recommendations that we usually share with our customers in the ADC team (Application Development Consultant ). Note that this list is not exhaustive and are general suggestions that can help you on your design process.

Configuration Management
The message here is clear, we need to move configurable options to a configuration file so the user can change it without recompiling the application. Yes, is quite clear but the problem is that developers usually overlook how this information is accessed and secured. We have seen many times user names and passwords on these files without any security! Not only have that, with time these configuration files grow to unmanageable levels that jeopardized the application execution.

Key Issues:

· Lack of or incorrect configuration information

· Sharing configurations around farms

· Not securing sensitive configuration information (exposing passwords/identities)

· Lack of security around the configuration files

Consider the following guideline:

· Use IIS sharing configuration features in order to deploy configuration files over a farm.

· Consider using least-privileged process and service accounts.

· Categorize the configuration items into logical sections, this method can help you secure different areas (features like configuration delegation in IIS are very helpful in this scenario)

· Encrypt sensitive information in your configuration store

· Restrict the access to your configuration information

· Provide a separate administrative application to deal with configuration files.

Pattern	Brief
Provider	Implement a component that exposes an API that is different from the client API in order to allow any custom implementation to be seamlessly plugged in.

Coupling and Cohesion
When you are designing components for your application you should ensure that are highly cohesive and loose coupling is used across layers. Coupling refers to the dependency between components and cohesion relies on the functionality that the component provides.

Key Issues:

· Incorrect grouping of functionality

· No clear separation between objects

· Tight coupling across layers

Consider the following guideline:

· Design for loose coupling between layers.

· Consider using abstraction to implement loose coupling between components.

· Consider using common interface definitions

· Use dependency inversion to decouple dependencies, depending on abstractions rather than concrete components.

· Divide your application functionality into logical layers; if you are dealing with customers you shouldn’t include your message binding properties on the same object.

· Design for high cohesion. If a component says “Customers” it should provide only customer functionality.

· While loose coupling requires more code, the benefits include a shortened dependency chain and simplify the building process.

Pattern	Brief
Composite view	Combine individual views into a composite view.
Inversion of Control	Populate any dependencies of objects on other objects or components that must be fulfilled before the object can be used by the client application.
Template View	Implement a common template view, and derive or construct views using the template view.
Two-Step View	Transform the model data into a logical presentation without any specific formatting, and then convert that logical presentation into the actual formatting required.
View helper	Delegate business data-processing responsibilities to helper classes.

Data Access
Separating the data access layer (DAL) is an important decision that improves the application maintainability and extensibility. This will allow you to easily change the repository or the logical structure of your data model without affecting the application functionality. It is recommended to implement an entity model to translate physical designs into business ready entities.

Key Issues:

· Per-user authentication and authorization when not needed

· Chatty database calls interfaces

· Data access code embedded with business logic

Consider the following guideline:

· Avoid coupling your application model to the database schema. Use abstraction models like the entity framework.

· Enforce data integrity in the database, not through data layer code.

· Move business logic to the application layer, avoid long stored procedures as they make applications harder to migrate and control.

· Open connections as late as possible and release them as early as possible.

· Avoid accessing the database from different layers, the DAL should be the only component that knows anything about the repository.

Pattern	Brief
Active record	Include a data access object within a domain entity.
Data mapper	Implement a mapping layer between objects and the database structure that is used to move data from one structure to another while keeping them independent.
Data Transfer Object	An object that stores the data transported between processes, reducing the number of method calls required.
Domain Model	A set of business objects that represents the entities in a domain and the relationships between them.
Query Object	An object that represents a database query.
Repository	An in-memory representation of a data source that works with domain entities.
Row data gateway	An object that acts as a gateway to a single record in a data source.
Table data gateway	An object that acts as a gateway to a table or view in a data source and centralizes all of the select, insert, update, and delete queries.
Transactional Script	Organize the business logic for each transaction in a single procedure, making calls directly to the database or through a thin database wrapper.
Table module	A single component that handles the business logic for all rows in a database table or view.

Exception Management
It is important to track all the application exceptions to make the system more reliable and to properly capture application defects. A crash can be very costly for customers and is not something that you want to re-experience in order to get more information. A proper exception management should provide you with enough information when the fault occurs, this should include as much information as possible in order to reproduce the scenario.

Key Issues:

· Unstable state exposure

· Revealing sensitive information to the user

· Using exceptions to control logic flow

· Inaccurate/non-existence logging information

Consider the following guideline:

· Do not reveal sensitive information in exception messages and log files. I have seen many websites showing the full stack when an error occurs!

· Let exceptions flow if they are unexpected, catching everything without proper logging may provide a false end user experience that can lead to corrupted entries.

· Design an appropriate exception propagation strategy.

· Send the information back to a central repository when possible to analyze trends when large user based is expected.

· Log information on common repositories, like log files, event logs or external web services.

Pattern	Brief
Exception Shielding	Prevent a service from exposing information about its internal implementation when an exception occurs

Layering
Proper layering design allows you to separate the functionality into different areas of concern. This will help you to group functionality and components that will make your system more predictable and able to scale out. Layers should have a well defined communication flow, for example, layer A can talk with layer B but not the opposite scenario.

Key Issues:

· Incorrect grouping of components within layers

· Not following layering and dependency rules

· Not considering physical boundaries

Consider the following guideline:

· They should be used as logical groups, for example, user interface, process layer, application layer, data layer.

· Components within a layer should be cohesive.

· Consider physical boundaries when designing layers

· Use interfaces to define each layer, this will allow proper communication and different deployment models.

· If you are running web applications consider using message-based interfaces to provide a stateless user interface.

· Provide a facade pattern to the process and application layers.

Pattern	Brief
Remote Facade	Creates a high-level unified interface to a set of operations or processes in a remote subsystem to make that subsystem easier to use, by providing a course-grained interface over fine-grained operations to minimize calls across the network.

The next part will complete the set of considerations, watch this space!

Design: SOA Taxonomy, an object oriented approach

Salva Patuel — Tue, 02 Sep 2008 14:05:00 GMT

An essential part of the SOA Governance is to properly identify the requirements in order to introduce or upgrade a service within your SOA model, this is commonly known and service and integration planning within the SOA lifecycle. This is all good in theory but the nightmares start when architects are trying to put it in practice.

As an application development consultant here at Microsoft we constantly find chaos in the SOA first attempts, the main reason behind this is the lack of services organization. This not only brings problems to the model that are expensive to change but does not shows business value to the stakeholders, as they cannot see any ROI in the implementation. As a result, the efforts are abandoned and the architectural model remains broken.

How do we help our customers to solve this issue? We usually take them a level higher within the abstraction layer, why do you need SOA? Which are the problems that you usually have? Which are the costs involved in changing your system? We really need to understand our driven forces that lead us to a new architectural paradigm.

But what about designing the services model? This is another area where confusion arises as architects ask themselves where they should start and how. The answer to this is enclosed on the services taxonomy. There are many categorizations and naming around taxonomy but I want to present a recommendation based on the Microsoft services experience.

We define four main categories that really help us to define the high level model. Let me explain each one of them.

· Entities Services: The entities encloses your business entities, these are independent actors within your business model. The entities do not provide business benefit acting alone as they don’t have the expertise around which other entities are around. They should be completely independent and should own the data repository. A good example of an entity service will be customers. Customers are nothing more than what the name says, it has and owns all the information about the entity “customer” but knows nothing about your business.

· Capabilities Services: This is the crucial part of your business; this is what you do to add value to your services. The capabilities know very well the entities and capabilities context where it works, as interacts and consumes services to deliver value. An important thing to understand is that they know about the capability but do not control the entities that consumes, this means that if a capability needs to alter an entity it should use the entity service responsible for that. The capability also owns its own repository and controls all the business logic associated with it. A good example of a capability is an order service. The order service will know everything about placing an order and will need entities in order to generate one, for example, the order will need the customer information that comes from the entity service.

· Application services: These services supports your business model, this means that provides auxiliary services to your entities and capabilities not directly associated with your system. This usually involves wrappers to third party application or bridges to other systems. A good example may be a service wrapper to a Remedy application.

· Bus services: This taxonomy groups all the support and infrastructure services that allow your entities and capabilities to work within the infrastructure policies. For example the security services that validate users can be grouped in this taxonomy.

As you see, with this categorization you can start to add services to your model. Where do you start? The easiest way to do it is asking yourself what your business does, what is the essence of it. Let’s imagine that you are the responsible for designing the SOA model for a large supermarket. The amount of services that you will need is massive but if I ask you about the essence of your business which will be the answer? Believe it or not this sounds easy but architects that are too embedded in the daily duties cannot properly answer the question. My model would be:

Look how simple it is, you just join customers with products and generate orders. Now, if I ask you to add these services in the taxonomy model you now know how to do it.

Remember that upon I have presented orders as the linking service between the entities this does not suggest hierarchy. All the services are at the same level as they can be accessed by an ESB (Enterprise service bus) or ISB (Internet service bus), or even simply your process layer. What is more, what you can do is apply the same model when you enter into the service design scope; this is for example when you design the internal taxonomy of “Orders”. This service will have again a process layer, entities and capabilities, but now only around the orders scope. Does this sound familiar? Well, it may, as it is a common model applied to the object oriented design.

Internally, these new entities and capabilities can be isolated components that are responsible for a solely function, for example, an internal process can be the workflow that triggers a new order and a capability may be altering the order value.

This can show you that applying the SOA governance model around taxonomy can help you and your developers to properly design services and object oriented components properly isolated and encapsulated, as is the same mindset. What is more, the WCF team is working in a “in-process” binding that will allow you to use a WCF communication with objects that today are part of your main process and tomorrow may develop into independent services just changing the configuration file! Isn’t it beautiful?

If your organization is facing these problems and you want Microsoft to support you and help you around your SOA initiative don’t hesitate the contact the “Application Development Consultant team” in Microsoft (http://www.microsoft.com/uk/adc)

Architect: SOA services lifecycle

Salva Patuel — Fri, 13 Jul 2007 16:11:00 GMT

Beyond the natural MSF lifecycle where all software development should fit in, there is a higher level of process lifecycle abstraction that relates to the service. Services are one of the most important backbones of a SOA model, where the business capabilities and activities interact with the entities to provide the solution response.

From the architectural point of view, services born, live and die. In order to use a common definition we are going to divide it in three states: expose, compose and consume. The architect is responsible to govern and manage this lifecycle with a clear visibility of the current status of each individual service. This will help to empower reusability and to have a better control when change occurs, what is more, is the recommended path to migrate architectures that contain legacy monolitic systems in order to reach the dynamic level on the application platform optimization model.

Expose: This first step consist in analysing the business drivers (processes) that are going to be addressed. This helps to indentify the necessary services that will solve the process requirement. With the services indentified the reuse (or new green field) services are exposed.

Compose: In this stage the serivces are composed depending on the type of process, if this requires an orchestration of many services this is the place to do it. This stage will incorporate the necessary knowledge to use the business services.

Consume: The client applications are able to discover and use the services based on the processes that govern them.

The lifecycle granularity can be further exploded into specific activities that will categorize the service in a specific domain. This domain has specific implications and the architect will need to embark into the different tasks and responsibilities that each step brings. This is not a fixed model; organizations can tailor it to fit their structure but is a good starting point to avoid missing the plot and rushing services into the model.

The picture shows how the architect is involved in both areas, the solution framework and the operations framework. This approach has worked quite well in many implementations here at Microsoft. If the architect only stays aware on the solution section it will miss the global view, how the services are performing and which ones are candidates for decommission or replacement. When a new service request arrives, the taxonomy of the model should help to identify which services are available; this is part of the analysis step. At this stage we can review the current entities, capabilities and activities and their functional domain. Is the request pushing for a completely new concept that the current services can not supply? This is the question to answer.

Once the service has been scoped and designed following the MSF guideline the building of the service is triggered as well as the testing and provisioning. I always like it to have a list with all my service listed, organized in a domain based ontology that gives me the full picture of what is going on. A graphical representation is always useful to visualize the services used by the different processes, I know that is hard to keep it up to date, but trust me, it really worth it.