Introduction
Sync Gateway is the synchronization server in a Couchbase Mobile deployment.
Couchbase Mobile brings the power of NoSQL to the edge and is comprised of three components:
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Couchbase Lite, an embedded, NoSQL JSON Document Style database for your mobile apps
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Sync Gateway, an internet-facing synchronization mechanism that securely syncs data between mobile clients and server, and
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Couchbase Server, a highly scalable, distributed NoSQL database platform
The following diagram describes the architecture for a typical deployment comprised of Couchbase Lite, Couchbase Server SDKs, Sync Gateway, and Couchbase Server.

Sync Gateway is designed to provide data synchronization for large-scale interactive web, mobile, and IoT applications. Commonly used features include:
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User authentication, ensuring that only authorized users can connect to Sync Gateway (see user authentication guide).
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Access Control, guaranteeing that only relevant documents are synced. Sync Gateway accomplishes this by examining document and applying business logic to decide whether to assign the documents to channels. Access control and ensuring that only relevant documents are synced are achieved through the use of channels and the Sync Function.