API Gateway(Reverse Proxy) - Application Programming Interface Gateway
======================================================================

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        **What is API Gateway?**

        An **API Gateway** is a server that acts as an **entry point** into a backend system or microservices architecture. It **manages, routes, secures, and monitors** API requests from clients to services.

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        **Why is API Gateway useful?**

        API Gateways are useful because they:
        - **Centralize access control** and authentication
        - **Enforce rate limiting and throttling**
        - Provide **load balancing and routing**
        - Handle **cross-cutting concerns** like logging, metrics, and caching
        - Simplify communication between external clients and complex backend services

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        **How it works?**

        The API Gateway receives client requests and:
        - **Authenticates** and **authorizes** them
        - **Transforms** or **validates** the request data if needed
        - **Routes** the request to the appropriate backend service
        - **Aggregates** data from multiple services if required
        - Sends back the response to the client
        It also manages **timeouts**, **retries**, **caching**, and **monitoring**.

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        **Where is API Gateway used?**

        API Gateways are widely used in:
        - **Microservices architectures**
        - **Cloud-native applications**
        - **Mobile and web backend systems**
        - **Serverless platforms**
        - Examples include AWS API Gateway, NGINX, Kong, Apigee, and Azure API Management.

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        **Which OSI layer does this protocol belong to?**

        API Gateway operates at the **Application Layer (Layer 7)** of the OSI model.

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        **Is API Gateway Windows specific?**

        No, API Gateways are **not Windows specific**. They can be deployed on any OS that supports network services, including Windows, Linux, and containerized environments like Docker/Kubernetes.

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        **Is API Gateway Linux specific?**

        No, API Gateways are **not Linux specific**. While many are optimized for Linux environments (e.g., NGINX), they are designed to run on multiple platforms.

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        **Which Transport Protocol is used by API Gateway?**

        API Gateways primarily use:
        - **HTTP/HTTPS**
        - Some may also support **WebSocket**, **gRPC**, or **TCP** depending on the implementation.

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        **Which Port is used by API Gateway?**

        Common default ports include:
        - **Port 80** for HTTP
        - **Port 443** for HTTPS
        - Custom ports can be configured as needed depending on the use case.

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        **Is API Gateway using Client server model?**

        Yes, an API Gateway is a key component of the **client-server model**.
        - **Clients** make requests to the API Gateway.
        - The **Gateway** handles the logic and forwards requests to the appropriate backend services (servers), then relays responses back to the client.

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        Topics in this section,

                * :ref:`Learnings in this section <API_Gateway_step1>`

                * :ref:`Terminology <API_Gateway_step2>`

                * :ref:`Version Info <API_Gateway_step3>`

                * :ref:`API_Gateway Version&IEEE Details <API_Gateway_step5>`

                * :ref:`API_Gateway Basic Setup on Ubuntu using IPv4 <API_Gateway_step18>`

                * :ref:`API_Gateway Basic Setup on Ubuntu using IPv6 <API_Gateway_step19>`

                * :ref:`API_Gateway Protocol Packet Details <API_Gateway_step6>`

                * :ref:`API_Gateway Usecases <API_Gateway_step7>`

                * :ref:`API_Gateway Basic Features <API_Gateway_step8>`
                    
                * :ref:`Reference links <API_Gateway_step17>`


.. _API_Gateway_step1:

.. tab-set::

    .. tab-item:: Learnings in this section

        * In this section, you are going to learn

.. _API_Gateway_step2:

.. tab-set::

    .. tab-item:: Terminology
        
       * Terminology


.. _API_Gateway_step3:

.. tab-set::

    .. tab-item:: Version Info
    
         * Version Info


.. _API_Gateway_step5:

.. tab-set::

    .. tab-item:: API_Gateway Version&RFC Details

        * rfc details

.. _API_Gateway_step18:

.. tab-set::

    .. tab-item:: API_Gateway Basic Setup on Ubuntu using IPv4

       * setup

.. _API_Gateway_step19:

.. tab-set::
  
   .. tab-item:: API_Gateway Basic Setup on Ubuntu using IPv6

     * setup
       
.. _API_Gateway_step6:

.. tab-set::

    .. tab-item:: API_Gateway Protocol Packet Details

        * packet details
       


.. _API_Gateway_step7:

.. tab-set::

    .. tab-item:: API_Gateway Usecases

       * usecases
        
        

.. _API_Gateway_step8:

.. tab-set::

    .. tab-item:: API_Gateway Basic Features
    
        * features 



.. _API_Gateway_step17:

.. tab-set::

    .. tab-item:: Reference links
     
       * Reference links