Add defensive warning for multiple Feign Client beans

Contribution Overview

The Engineering Context

This contribution was made to the spring-cloud/spring-cloud-openfeignopen-source repository. The work involved understanding the existing codebase, identifying the underlying engineering problem, implementing a focused solution, and validating the change against the project's existing behaviour and testing standards.

Engineering Problem

Understanding the Problem

Incorrect Feign client configuration can result in multiple Client beans or non-singleton Client instances being created inside a Feign client context. This can potentially create multiple underlying HTTP connection pools and increase resource consumption.

Solution

Implementation Approach

Added a defensive warning in FeignClientFactoryBean to improve visibility when multiple Client beans are detected. Also updated the documentation to clarify that custom Feign Client beans should normally use singleton scope. The change improves detection of potentially expensive misconfiguration without changing existing bean lifecycle behaviour.

Technologies

Engineering Stack