While the SOA pattern is very powerful and offers unparalleled levels of abstraction, heterogeneous connectivity, service orchestration, and the promise of aligning business goals with IT capabilities, it is nevertheless complex, expensive, ubiquitous, difficult to understand and implement, and is usually overkill for most applications. The microservices architecture pattern solves many of the common issues found in both monolithic applications as well as service-oriented architectures. For each step in the initial event, the event mediator sends out a specific processing event to an event channel, which is then received and processed by the event processor. This pattern gets its name from the concept of tuple space, the idea of distributed shared memory. High scalability is achieved by removing the central database constraint and using replicated in-memory data grids instead. Application data is kept in-memory and replicated among all the active processing units. The event channels contained within the broker component can be message queues, message topics, or a combination of both. This is a fairly common practice in most business applications implementing the microservices architecture pattern, trading off the redundancy of repeating small portions of business logic for the sake of keeping service components independent and separating their deployment. Internet browsers are another common product example using the microkernel architecture: viewers and other plug-ins add additional capabilities that are not otherwise found in the basic browser (i.e., core system). One of the powerful features of the layered architecture pattern is the separation of concerns among components. One common way of implementing this is through some sort of plug-in registry. Using the microkernel architecture pattern can solve many of these issues. Paraphrased from the book's figure 2.13, the erroneous implementation creates this dependency graph: The arrows show the direction of dependencies; i.e. The deployment-manager component manages the dynamic startup and shutdown of processing units based on load conditions. The black arrows show the request flowing down to the database to retrieve the customer data, and the red arrows show the response flowing back up to the screen to display the data. The layers are organized hierarchically by the principles of generalization and specialization. Perhaps the best example of the microkernel architecture is the Eclipse IDE. This pattern is the de facto standard for most Java EE applications and therefore is widely known by most architects, designers, and developers. This might require conversion of message types and etc. For very large applications requiring much more sophisticated orchestration (including steps involving human interactions), you can implement the event mediator using a business process manager (BPM) such as jBPM. While the granularity of the event-processor component can vary from fine-grained (e.g., calculate sales tax on an order) to coarse-grained (e.g., process an insurance claim), it is important to keep in mind that in general, each event-processor component should perform a single business task and not rely on other event processors to complete its specific task. Â. Another advantage of this pattern is that it provides the capability to do real-time production deployments, thereby significantly reducing the need for the traditional monthly or weekend “big bang” production deployments. The type of connection you use depends on the type of application you are building (small product or large business application) and your specific needs (e.g., single deploy or distributed deployment). For example, a single event to place a stock trade might require you to first validate the trade, then check the compliance of that stock trade against various compliance rules, assign the trade to a broker, calculate the commission, and finally place the trade with that broker. The rating for each characteristic is based on the natural tendency for that characteristic as a capability based on a typical implementation of the pattern, as well as what the pattern is generally known for. It is important to note that the event mediator doesn’t actually perform the business logic necessary to process the initial event; rather, it knows of the steps required to process the initial event.Â, Event channels are used by the event mediator to asynchronously pass specific processing events related to each step in the initial event to the event processors. For example, in a relaxed layered system (as opposed to a strict layered system) a layer can also depend on all the layers below it. It is a good architecture choice for smaller web-based applications with variable load (e.g., social media sites, bidding and auction sites). This is relatively easy and inexpensive, and sometimes works to address the bottleneck issues. For example, a plug-in for tax software that flags high-risk tax audit items might have a registry entry that contains the name of the service (AuditChecker), the data contract (input data and output data), and the contract format (XML). 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