Orchestration is the automated arrangement, coordination, and management of computer systems, middleware, and services.
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Usage
Orchestration is often discussed as having an inherent intelligence or even implicitly autonomic control, but those are largely aspirations or analogies rather than technical descriptions. In reality, orchestration is largely the effect of automation or systems deploying elements of control theory.
This usage of orchestration is often discussed in the context of service-oriented architecture, virtualization, provisioning, converged infrastructure and dynamic datacenter topics. Orchestration in this sense is about aligning the business request with the applications, data, and infrastructure. It defines the policies and service levels through automated workflows, provisioning, and change management. This creates an application-aligned infrastructure that can be scaled up or down based on the needs of each application. Orchestration also provides centralized management of the resource pool, including billing, metering, and chargeback for consumption. For example, orchestration reduces the time and effort for deploying multiple instances of a single application. And as the requirement for more resources or a new application is triggered, automated tools now can perform tasks that previously could only be done by multiple administrators operating on their individual pieces of the physical stack.
A somewhat different usage relates to the process of coordinating an exchange of information through web service interactions. (See also service-oriented architecture, and web service choreography.) Applications that decouple the orchestration layer from the service layer are sometimes called agile applications.
A distinction is often made between orchestration (a local view from the perspective of one participant) and choreography (coordination from a global multi-participant perspective, albeit without a central controller).
Cloud computing
Cloud computing introduces more-granular and specific meanings of the terms "workflows" and "processes" as used in different domains. Processes can be identified at both the level of inter-company business and the level of wide area network ("the cloud") operations. An "orchestrator" is understood to be the entity which manages complex cross-domain (system, enterprise, firewall) processes and handles exceptions. Since an orchestrator is valuable in fulfillment, assurance, and billing processes, service-aware incarnations of an orchestrator should be capable of adjustments based on feedback from monitoring tools. At the most basic level, an orchestrator is a human.
The main difference between a workflow "automation" and an "orchestration" (in the context of cloud computing) is that workflows are processed and completed as processes within a single domain for automation purposes, whereas orchestration includes a workflow and provides a directed action towards larger goals and objectives.
In this context, and with the overall aim to achieve specific goals and objectives (described through quality of service parameters), for example, meet application performance goals using minimized cost and maximize application performance within budget constraints, cloud management solutions also encompass frameworks for workflow mapping and management.
Cloud service orchestration consists of these elements:
Orchestration is critical in the delivery of cloud services for these reasons: