* Integration architecture connects various components of the system and it is these connections that describe the integration architecture.
* The technical architecture describes the implementation of the previous layers. It itself is also divided into layers, but these layers are not abstractions, but are a technical implementation in relation to the client. These layers are also called a stack, since they are not located from the user of the business layer one by one in a specific order and not a single layer can be skipped, while the layers of architecture describe the architecture in a different way, can be supplemented and changed, but we adhere to the set of layers accepted in TOGAF. So, the stack of WEB-applications consists of:
** Application layer – the layer with which users directly interact and which provide processes and is implemented using WEB-interfaces in browsers. Execution of business logic at the level of WEB-interfaces is unacceptable – all work is delegated to the underlying layer.
** The network layer ensures the operation of WEB-interfaces in the user's browsers, transmitting data. The upper layer of applications is needed by users who are comfortable using the graphical interface and so that any routine actions are performed for them. The network layer provides communication for server applications such as WEB servers and DBMS.
** The hardware layer is represented by runners. These devices can be hardware-based with varying degrees of versatility. For example, a load balancer can be purely hardware, it can be hardware with changeable firmware, it can be software executable on a general purpose computer of the x86 type, it can be launched both directly and in a virtual machine, and in a container – all these are implementation details.
** The storage layer is made up of storage devices. These devices can be specialized devices such as IBM DataPower or regular RAID with a control module. The data in it completely describes the state and is the result of work, and the previous layers are only needed to change and provide convenient access to users.
If necessary, other layers can be implemented, for example:
* information security layer implemented by the firewall;
* a layer of basic containers;
* layer of local fault tolerance (HA) using the example of the Kubernetes layer;
* containerization layer;
* virtualization layer;
* a layer of resilience to failures implemented by load balancers on different DataCenter.
In any case, the number of layers is standardized, those that differ are indicated, so that each layer belongs to a specific info-structural department and an operation department.
Let's pay more attention to the integration architecture, since this is the most critical layer for the architecture. In this layer, connections can be presented both in a graphical form (in the arrows on the diagrams between systems), and in a tabular form – in the form of a description of the supplier, consumer and contract (the supplier's obligations to the contractor). The arrows point from the supplier to the consumer, that is, in the direction of the integration flow, while the service modules are not indicated. Depending on whether the parameters are functional or non-functional, they will be described either by API or SLA. Also, depending on whether the connections are inside or from outside to inside and outside. The first type is more visual, and the second allows you to give more detailed characteristics.
The system itself can be integrated in different ways, such as:
* direct integration (communication via API point-to-point, advantages: minimum overhead, disadvantages: two-way revision of systems is required, complexity of change management, complexity of scaling, no reuse);
* using gateways (communication through the API of an integration layer, such as a queue with a firewall, advantages: minimum overhead, unified API, disadvantages: complexity of change management, complexity of scaling, no reuse);
* Enterprise data bus or enterprise service bus (ESB) provides asynchronous umbrella integration based on the principles of event and service approach (SOA, service-oriented architecture). The corporate data bus is able to flexibly route messages from one service to another. (advantages: unification, reusability due to SOA, replaceability of services due to SOA, disadvantages: an expensive solution in many applications, delivery time from tens of milliseconds);
* Service Mesh, like ESB, is umbrella, but applications do not need to integrate with it, since applications running in a containerized environment immediately receive integration. (microservices, advantage: minimum overhead, not noticeable for application developers);
* Integration file gateways and point-to-point file transfer (file overload). Point-to-point file transfer is the same point-to-point transfer, but it allows you to transfer large data in exchange for the transmission speed (advantage: it is possible to transfer very large amounts of data, high delivery guarantee, weak connectivity of integrated systems, greater control, broadcast mode, disadvantages: transmission speed, possibility of desynchronization, high security requirements). Communication protocols are CIFS (Common Internet File System), NFS (Network File System extends the local file system) and S3 (Simple Storage Service provides access to object storage such as Minio and Ceph) and transfer protocols HTTPS (HTTP + SSL), SFTP (SSH + SSL) and FTPS (FTP + SSL). From the point of view, records can be divided into block (disk) and object (writing to the key-value database: Bucket).
Systems can communicate in various ways:
* integration request (normal synchronous request-response),
* remote procedure call (RPC),
* sending a command to the queue (from the supplier to the consumer directly through the event queue),
* publish-subscribe, Push-Sub (sending events to a common queue, from which groups of events are retrieved from the system in advance, undefined by the provider),
* packet data transmission,
* transferring files to storage,
* streaming data.
The interactions themselves should be described, and preferably unified. To describe functional or non-functional parameters (response time, availability, message size, bandwidth) of interactions between the supplier and the consumer, a Contract is used, which the supplier undertakes to fulfill. Functional parameters are described using the Application Programming Interface (API). Service APIs can be divided into groups based on message format (DTO, JSON, XML, binary) or protocol (HTTP, REST, SOAP). It is important to specify in the API contract: ID, name, version, purpose, template, specification of input and output parameters. The API itself will contain methods (encouraging the consumer to take data, change, allocate, etc.). Parameters passed in a method are described by a method specification, for example, using OpenAPI or Swagger. For many languages, and primarily for the Java language, you can automatically generate a specification for OpenAPI using Swagger by Javadoc annotations (by special comments) in the code. The specification will be displayed in both text formats (JSON and YAML) and graphical. For ease of design, you can use the Swagger Editor (https://swagger.io/tools/swagger-editor/). This helps to organize automated contract testing. In general, the presence of the specification helps to organize API-first development, when the API specification is first written, and already the application code is developed for it, implementing it.