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# Selenium Grid Server
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Selenium Grid server enables distributed WebDriver test execution across multiple browsers and operating systems. It consists of a hub-and-node architecture where the hub acts as a central registry and router for WebDriver commands, while nodes provide actual browser instances. The server supports multiple browser types and can distribute test execution based on desired capabilities.
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## Package Information
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- **Package Name**: org.seleniumhq.selenium:selenium-server
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- **Package Type**: maven
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- **Language**: Java
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- **Version**: 3.141.59
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- **Installation**: `<dependency><groupId>org.seleniumhq.selenium</groupId><artifactId>selenium-server</artifactId><version>3.141.59</version></dependency>` or standalone JAR download
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## Core Imports
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Primary entry points for Selenium Grid server:
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```java
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// Main Grid launcher (recommended for v3.141.59)
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org.openqa.grid.selenium.GridLauncherV3
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// Modern Grid interface (limited support in v3.141.59)  
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org.openqa.selenium.grid.Main
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// Standalone server entry point
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org.openqa.selenium.remote.server.SeleniumServer
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```
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## Basic Usage
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Start the server using Java with the standalone JAR:
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```bash
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java -jar selenium-server-standalone-3.141.59.jar <command> [options]
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```
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Traditional Grid 3 syntax (recommended for v3.141.59):
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```bash
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# Start complete Grid in single process
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java -jar selenium-server-standalone-3.141.59.jar -role standalone -port 4444
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# Start distributed setup
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java -jar selenium-server-standalone-3.141.59.jar -role hub -port 4444
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java -jar selenium-server-standalone-3.141.59.jar -role node -hub http://hub-host:4444
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```
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Modern command syntax (limited support in v3.141.59):
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```bash
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java -jar selenium-server-standalone-3.141.59.jar standalone --port 4444
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java -jar selenium-server-standalone-3.141.59.jar hub --port 4444
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java -jar selenium-server-standalone-3.141.59.jar node --distributor http://hub-host:4444
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```
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## Architecture
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The Selenium Grid server is built around several key architectural components:
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- **CLI Commands**: Traditional Grid 3 role-based commands plus limited modern command support
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- **HTTP REST API**: WebDriver protocol endpoints plus Grid-specific management APIs  
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- **Configuration System**: Multi-layered configuration with CLI args, environment variables, and system properties
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- **Service Discovery**: ServiceLoader-based command registration and auto-discovery
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- **Session Management**: Distributed session tracking across multiple nodes
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- **Request Routing**: Intelligent routing based on browser capabilities
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## Capabilities
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### Command Line Interface
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CLI interface providing traditional Grid 3 role-based commands and limited modern command support for different deployment scenarios.
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```bash { .api }
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# Traditional Grid 3 syntax (recommended)
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java -jar selenium-server-standalone-3.141.59.jar -role <hub|node|standalone> [options]
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# Modern command syntax (limited support)
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java -jar selenium-server-standalone-3.141.59.jar <command> [options]
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# Commands: standalone, hub, node, router, distributor, sessions
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```
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[Command Line Interface](./cli.md)
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### HTTP REST API
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REST API endpoints for WebDriver protocol implementation, session management, node registration, and Grid administration.
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```java { .api }
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// Core endpoint patterns
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POST   /session                        // Create new WebDriver session
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GET    /session/{sessionId}/*          // WebDriver commands  
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POST   /se/grid/session/{sessionId}    // Register session with Grid
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GET    /status                         // Get component status
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POST   /se/grid/distributor/node       // Register node with distributor
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```
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[HTTP REST API](./rest-api.md)
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### Configuration Management
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Flexible configuration system supporting multiple sources with well-defined precedence rules for enterprise deployment scenarios.
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```java { .api }
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// Configuration interface
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interface Config {
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    String get(String section, String option);
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    int getInt(String section, String option);
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    boolean getBool(String section, String option);
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}
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// Configuration sections: server, distributor, sessions, node
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```
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[Configuration Management](./configuration.md)
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### Extension Points
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Public interfaces and abstract classes for customizing Grid behavior, including session factories, command handlers, and component implementations.
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```java { .api }
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// Core extension interfaces
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interface CommandHandler {
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    void execute(HttpRequest req, HttpResponse resp) throws IOException;
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}
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interface SessionFactory {
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    boolean isSupporting(Capabilities capabilities);
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    Optional<ActiveSession> apply(Set<Dialect> downstreamDialects, Capabilities capabilities);
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}
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```
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[Extension Points](./extensions.md)