1. Key Difference 1: Performance Testing Tool Comparison: Gatling is a leading open-source load and performance testing tool developed using Scala with a strong focus on asynchronous, non-blocking processing. On the other hand, Locust is also an open-source performance testing tool, but it is written in Python and emphasizes simplicity and flexibility.
2. Key Difference 2: Language and Support: Gatling is primarily based on Scala, a programming language widely used in the industry. It has an active and supportive community that contributes to its development and provides solutions. In contrast, Locust is based on Python, which is also a widely adopted language, but it has a smaller community and may have limited support and resources compared to Gatling.
3. Key Difference 3: Testing Paradigm: Gatling uses an event-driven, simulations-based approach where users define scenarios using a Domain-Specific Language (DSL) for writing simulations, allowing for more precise control over the test flow. Locust, on the other hand, uses an imperative approach, allowing users to define the test flow directly in Python code.
4. Key Difference 4: Modularity and Extensibility: Gatling provides a modular and extensible architecture, allowing users to create custom components and plugins to extend its capabilities as per their requirements. In contrast, Locust offers limited modularity and extensibility options compared to Gatling, which might restrict its customization possibilities.
5. Key Difference 5: Real-time Monitoring and Reporting: Gatling offers comprehensive real-time monitoring and reporting features, including intuitive and detailed graphical representations, enabling users to analyze test results effectively. Locust, while providing basic monitoring and reporting, may not provide the same level of detailed graphical analysis as Gatling.
6. Key Difference 6: Maturity and Enterprise Support: Gatling has been in the market for a longer time and is well-established, often used for enterprise-grade performance testing. It has a dedicated support team and offers enterprise support services. Locust, being relatively newer, may have limited enterprise support options and might be more suitable for smaller-scale performance testing projects.

In Summary, Gatling and Locust differ in the programming language, testing paradigm, modularization, real-time monitoring, maturity, and enterprise support, making them suitable for different user preferences and testing needs.