Value of Service Interfaces

January 4, 2015

Wrote earlier about why interfaces are important and in this post want to elaborate on their advantages for building reusable services. Service interfaces contain only the operation or method definitions and have no implementations. They can be used in a variety of ways:

  • Package service interfaces into a separate artifact to make it easy for client teams to integrate with services without pulling in bulky set of transitive dependencies
  • Bind the interfaces to one or more transport / integration technology via standard Dependency Injection (DI). For example, service interfaces can be integrated with a REST-ful Resource or a EMS listener.
  • Service interfaces can be backed by stub and/or mock implementation for automated unit and regression testing.
  • Service interfaces can be decorated with common cross-cutting concerns to separate them from the implementation. This is the strategy implemented via the Java Dynamic Proxy example.
  • Service interfaces can be implemented as a proxy to a remote implementation. For example, the client invokes the functionality via the interface but the runtime implementation makes a call to a server side API. This is useful if your teams need the flexibility to swap local / remote implementations depending on performance / dependency management related requirements
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Make Services Fault Tolerant & Supportable for Production Use

January 3, 2015

A lot of teams are building services for clients both internal and external to your organization. Typically, there is quite a bit of focus on succeeding from a functional sense – did we get the key requirements addressed? does it cover the plethora of rules across markets / jurisdictions? and so on. Some of the more experienced teams, consider the non-functional aspects as well – e.g. logging, auditing, exception handling, metrics, etc. and I talked about the value of service mediation for addressing these in an earlier post.

There is an expanded set of capabilities that are also necessary when addressing non-functional requirements – those that are very relevant specially when your service grows in popularity and usage. They fall under two categories: operational agility and fault-tolerance.  Here are a few candidate capabilities in both these categories:

Operational Agility / Supportability:

  • Ability to enable / disable both services and operations within a service
  • Ability to provision additional service instances based on demand (elastic scaling)
  • Maintenance APIs for managing resources (reset connection pool, individual connections, clear cached data, etc.)
  • Ability to view Service APIs that are breaching and ones that are the risk of breaching operational SLAs
  • Model and detect out of band behavior with respect to resource consumption, transaction volumes, usage trends during a time period etc.

Fault Tolerance:

  • Failing fast when there is no point executing operations partially
  • Ability to detect denial of service attacks from malicious clients
  • Ability to gracefully handle unexpected usage spikes via load shedding, re-balancing, deferring non-critical tasks, etc.
  • Detecting failures that impact individual operations as well as services as a whole
  • Dealing with unavailable downstream dependencies
  • Leveraging time outs when integrating with one or more dependencies
  • Automatically recovering from component failures

In future posts, I will expand on each of these topics covering both design and implementation strategies. It is also important to point out that both these aspects are heavily interconnected and influence each other.


Client Integration Mini-Checklist for Services

May 27, 2012

Working with clients who are consuming your services? Here is a mini-checklist of questions to ask:

  1. While executing request/reply on the service interface is there a timeout value set on the call?
  2. Is there code/logic to handle SOAP Faults /system exceptions when invoking the service?
  3. Is building service header separated from the payload? This will facilitate reuse across services that share common header parameters
  4. If there are certain error codes that the calling code can handle, is there logic for each of them?
  5. Is the physical end point information (URL string for HTTP, Queue connection and name for MQ/EMS) stored in an external configuration file?
  6. Is UTF-8 encoding used while sending XML requests to the service i.e. by making use of platform-specific UTF encoding objects?
  7. If using form-encoding are unsafe characters such as ‘&’, ‘+’, ‘@’ escaped using appropriate %xx (hexadecimal) values?
  8. While processing the service response is the logic for parsing/processing SOAP and service-specific headers decoupled from processing the business data elements?
  9. Is the entire request/reply operation – invocation and response handling logic – encapsulated into its own class or method call?
  10. While performing testing, is the appropriate testing environment URL/queue manager being used?
  11. Is a valid correlation id being used in the service request? This is very essential for aynchronous request/reply over JMS (JMS Header) or HTTP (callback handler)

Detect Service Availability Issues Before Your Clients Do

January 17, 2012

When service capabilities get reused across applications and processes, high availability becomes imperative – key question: do you detect availability issues before your clients do? This is important for several reasons:

  • Unlike stand alone applications/processes, shared services impact several consumers. Not every consumer might be okay with your service being unavailable for an extended period of time. The same service might be in the critical path for some and not so much for others
  • For some service capabilities, running them in a partial mode might be acceptable – e.g.  operating out of a cached copy of data rather than fetching it from a live database, or servicing only read only operations during an unexpected outage, etc.
  • Some consumers might have regulatory processes that are dependent on services being available – a service being unavailable might cause SLA breaches

Finally, consumer trust is key for systematic reuse – if they perceive service availability as a limiting factor, it will be harder to convince them to use services – including current and upcoming integrations


Governance Enables Service Reuse – New Podcast Episode

December 27, 2011
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New episode added to the Software Reuse Podcast Series on service governance covering design, implementation, testing, and provisioning and how they enable reuse.

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Track Service Reuse Metrics

December 24, 2011

Service driven systematic reuse takes conscious design decisions, governance, and disciplined execution – project after project. In order to sustain long running efforts such as service orientation, it is critical to track, report, and get buy-in from senior management in the organization. So what metrics are useful? Here are a few:

  • Total number of service operations reused in a time period
  • Total effort saved due to systematic reuse in a time period
  • Number of new service consumers in a time period
  • Number of new consumer integrations in a time period (this includes integrations from both new and existing consumer
  • Service integrations across transports/interface points (for instance, the service operation could be accessed SOAP over HTTP, or as SOAP over JMS, or REST, etc.)

What metrics do your teams track?


5 Service Governance Practices for Effective Reuse

December 24, 2011

Pursuing service based systematic reuse or business process development? Then, these five practices will help your teams achieve increased level of service reuse.

  1. Manage a common set of domain objects that are leveraged across service capabilities. This could be a library of objects (e.g. Plain Old Java Objects) or XML Schema definitions or both. Depending on the number of service consumers and the complexity in the domain, there will be need for supporting multiple concurrent versions of these objects.
  2. Provide common utilities for not only service development but WSDL generation, integration and performance testing, and ensure interoperability issues are addressed
  3. Appropriate functional experts are driving the service’s requirements and common capabilities across business processes are identified early in the software development lifecycle
  4. Governance model guidelines are clearly documented and communicated  – for example, there are a class of changes that can be made to a public interface such as a WSDL that don’t impact existing service clients and there are some that do.
  5. Performance testing needs to be done not only during development but during service provisioning – i.e. integrating a new service consumer. If your teams aren’t careful, one heavy volume consumer, can overwhelm a service impacting both new and existing consumers. Execute performance testing in an automated fashion – every time you integrate with a new client to reduce risks of breaching required SLAs

What additional practices do your teams follow?


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