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INDEPENDENT SYSTEMS ARCHITECTURE

Principles for Microservices

 * Home
 * Reasoning
 * Non Principles
 * FAQ
 * Links
 * Discussion
 * Privacy


INTRODUCTION

ISA (Independent Systems Architecture) is a collection of best practices based
on experience in particular with microservices and Self-contained Systems and
the challenges faced in those projects.

Far too often microservices are adopted but the projects then fail to succeed.
This set of best practices ensures that common pitfalls are avoided and the
promised benefits of microservices are achieved.

However, ISA principles don’t always apply - see the FAQ for details.



Speaker Deck PowerPoint


TERMS

The principles use “must” for aspects that cannot be compromised about and must
be present in the system. “Should” is used in principles that have a lot of
benefits, but can be left out in some cases. The principles described here talk
about a system. Usually the IT landscape of an enterprise contains many systems.
Each system might be built with a different set of principles or maybe even a
completely different approach.


PRINCIPLES

 1. The system must be divided into modules that provide interfaces. Access to
    other modules is only possible through these interfaces. Therefore modules
    must not directly depend on implementation details of other modules, e.g.
    the internal data representation in a database. The rest of the principles
    define how modules might be implemented, and how ISA differs from other
    modularization approaches.

 2. The system must have two clearly separated levels of architectural
    decisions:
    * The Macro Architecture comprises decisions that cover all modules. All
      further principles are part of the Macro Architecture.
    * The Micro Architecture considers decisions which may be taken individually
      for each module.

 3. Modules must be implemented as separate processes, containers, or virtual
    machines to maximize independence and enable a separation between Macro and
    Micro Architecture.

 4. The choice of integration and communication options must be limited and
    standardized for the system. The integration might be done with synchronous
    or asynchronous communication, and/or on the UI level. Communication must
    use a limited set of protocols like RESTful HTTP or messaging. It might make
    sense to use just one protocol for each integration option.

 5. Metadata, e.g. for authentication, must be standardized. Otherwise the user
    would need to log in to each microservices. This might be done using e.g. a
    token that is transferred with each call / request. Other examples might
    include a trace id to track a call and its dependent calls through the
    microservices.

 6. Each module must have its own independent continuous delivery pipeline.
    Tests are part of the continuous delivery pipeline so the modules must be
    tested independently.

 7. Operations should be standardized. This includes configuration, deployment,
    log analysis, tracing, monitoring, and alerting. There might be exceptions
    from the standard if a module has very specific requirements.

 8. Standards for operations, integration, or communication should be enforced
    on the interface level. For example, the communication protocol and data
    structures could be standardized to a specific JSON payload format exchanged
    using HTTP, but every module should be free to use a different REST
    library/implementation.

 9. Modules must be resilient. They must compensate unavailable modules or
    communication problems. They must be able to cope with unexpected shutdowns
    without losing data or state. It must be possible to move them to other
    runtime environments (hosts, networks, config etc).

NOTE: We created a dedicated page to express the reasoning behind these
principles.


PRESENTATION

You can download a presentation about ISA. It is licensed under a Creative
Commons Attribution-ShareAlike 3.0 Unported License so you can use it for your
purposes.

ISA is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported
License.

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