Segment Evaluation in Client-Side vs Server-Side SDKs

This guide details how VWO's Feature Management & Experimentation (FME) SDKs handle segmentation, particularly based on Location, User Agent (UA), and User Attributes — differently for client-side and server-side implementations.

Overview

Segmentation is a critical part of delivering personalized experiences. VWO supports advanced segmentation based on:

• 🌍 Location (derived via IP)
• 🧭 User Agent (device/browser type)
• 🧑‍💼 User Attributes (e.g., logged-in state, subscription plan)

Depending on whether you use client-side or server-side SDKs, the evaluation workflow varies. Here's a visual representation:

Client-side vs Server-side Complex Segment Evaluation

flowchart TD
    A[User's Browser / Mobile App] --> B[SDK Requires Complex Segmentation Evaluation]
    B --> C[Client-side SDK]
    B --> C2[Server-side SDK]

    %% Client-Side SDK Branch
    C --> D[Communicates with VWO CDN]
    D --> E[DaCDN auto-evaluates IP, UA]
    E --> F[Segments Evaluated at Edge]
    F --> G[Evaluate Feature Flag]

    %% Server-Side SDK Branch
    C2 --> H[Requires VWO Gateway Setup]
    H --> I[Your Server Extracts IP/UA]
    I --> J[Forwards Context to Gateway]
    J --> K[Gateway Evaluates Segmentation]
    K --> L[Returns Segment Info to SDK]
    L --> M[Evaluate Feature Flag]

    %% Styling
    class B,D,E,F,G,H,I,J,K,L,M step;
    class C decision;
    class C2 decision;

    classDef step fill:#eef,stroke:#333,stroke-width:1px,color:#000;
    classDef decision fill:#cfe2f3,stroke:#333,stroke-width:1px,color:#000;

Client-Side SDKs: Automatic Segmentation via DaCDN

How it Works

VWO’s client-side SDKs leverage the VWO DaCDN, an intelligent CDN layer, to automatically evaluate segments using the request's IP and User-Agent. These values are implicitly available to DaCDN because it is invoked directly from the user's browser/device.

⚙️

Note

No extra code is needed to pass IP or UA from your application.

Benefits

• Zero configuration required
• Automatic targeting on geo/location and device/browser
• Fast, edge-based evaluation
• No backend setup required

Ideal Use Cases

• A/B testing or personalization for web/mobile users
• Segmentation based on country/region/device/browser
• Experiments running at scale with minimal infrastructure overhead

Server-Side SDKs: Requires Gateway Service

In server environments (e.g., Node.js, Python, Java, Ruby, PHP, .NET, and Go), IP and UA are not available by default to the SDK. These attributes live in your server's request context.

To support complex segments like Location and User Agent, you must:

1. Set up Gateway Service.
2. Forward IP/UA headers to the Gateway via SDK APIs.
3. Let Gateway handle segment evaluation.

Why This Difference?

Server-side SDKs run in a backend context without automatic access to:

• Client IP addresses (due to proxies/load balancers)
• User agent strings (only available in incoming HTTP requests)

Ideal For

• Teams needing complete control over request flows.
• Advanced integrations where client context is manually passed.

📘

Note

For fast and frictionless implementation of advanced segment targeting (location, user-agent, and more), we strongly recommend using Client-Side SDKs wherever feasible. If you're using server-side SDKs, ensure VWO Gateway is correctly set up for similar capabilities.