Feign mixing up two separate request/response within the same client

Hi

I have been using feign for calls from one spring boot application to another in an infrastructure which has a large volume of API calls. Recently I have been getting an intermittent issue which says that the response received to one of the feign client calls cannot be resolved to the Object that it expects. Upon further debugging, I saw that the response received on this feign call is an unexpected response as it is supposed to be received on a completely different feign call.

Feign logs:

Jul 5, 2023 @ 18:33:44.518	[PlaceholderResource#getPlaceholderType] ---> GET http://placeholder-url.com/v5/getplaceholdertype/123/type/1234 HTTP/1.1
Jul 5, 2023 @ 18:33:44.518	[PlaceholderResource#getPlaceholderType] X-MM-CORRELATION-ID: correlation-id-1
Jul 5, 2023 @ 18:33:44.518	[PlaceholderResource#getPlaceholderType] ---> END HTTP (0-byte body)
Jul 5, 2023 @ 18:33:44.518	[PlaceholderResource#getPlaceholderType] <--- HTTP/1.1 200 OK (0ms)
Jul 5, 2023 @ 18:33:44.518	[PlaceholderResource#getPlaceholderType] content-type: application/json
Jul 5, 2023 @ 18:33:44.518	[PlaceholderResource#getPlaceholderType] link: <http://placeholder-url.com/v5/api/getplaceholderobject/123/user/123123/placeholderobject?param1=123123&param2=true&param3=false&page=-1&size=100>; rel="last" <http://placeholder-url.com/v5/api/getplaceholderobject/123/user/123123/placeholderobject?param1=123123&param2=true&param3=false&page=-1&size=100>; rel="first"
Jul 5, 2023 @ 18:33:44.519	[PlaceholderResource#getPlaceholderType] vary: accept-encoding
Jul 5, 2023 @ 18:33:44.519	[PlaceholderResource#getPlaceholderType] x-mm-correlation-id: correlation-id-2
Jul 5, 2023 @ 18:33:44.518	[PlaceholderResource#getPlaceholderType] date: Wed 05 Jul 2023 14:33:34 GMT
Jul 5, 2023 @ 18:33:44.519	[PlaceholderResource#getPlaceholderType] x-total-count: 0
Jul 5, 2023 @ 18:33:44.519	[PlaceholderResource#getPlaceholderType] x-result-count: 0-0/0
Jul 5, 2023 @ 18:33:44.519	[PlaceholderResource#getPlaceholderType] []
Jul 5, 2023 @ 18:33:44.519	[PlaceholderResource#getPlaceholderType] <--- END HTTP (2-byte body)
Jul 5, 2023 @ 18:33:44.519	[PlaceholderResource#getPlaceholderType] 

The URL returned in the link header is sent back from a different URL used for getPlaceholderObjects API and not the getPlaceholderType API

This [] response is expected for the getPlaceholderObjects API. Even the correlation ID header we're receiving is for a different API call which is supposed to be running in a different thread.

Feign interface:

@FeignClient(
		name = "placeholderResource",
		url = "${placeholder.api.url}")
@Headers("Content-Type: application/json")
public interface PlaceholderResource {

	/**
	 * Get placeholder type
	 */
	@GetMapping(
			value = "/getplaceholdertype/{referrerId}/type/{placeholderTypeId}")
	PlaceholderType getPlaceholderType(@PathVariable("referrerId") final Integer referrerId,
			@PathVariable("placeholderTypeId") final Long placeholderTypeId);

	/**
	 * Get placeholder object(s)
	 */
	@GetMapping(
			value = "/getplaceholderobject/{referrerId}/user/{userId}/placeholderobject")
	PlaceholderObject[] getPlaceholderObjects(@PathVariable("referrerId") final Integer referrerId,
			@PathVariable("userId") final Long userId,
			@RequestParam("param1") final List<Long> param1,
			@RequestParam("param2") final String param2,
			@RequestParam("param3") final Boolean param3);
}

Feign configuration:

/**
 * Configuration class for feign client(s).
 */
@Configuration
@EnableDiscoveryClient
public class FeignConfiguration {

	@Bean
	public FeignClientEncodingProperties feignClientEncodingProperties() {
		return new FeignClientEncodingProperties();
	}

	@Bean
	public ErrorDecoder feignErrorDecoder() {
		return new CustomFeignErrorDecoder();
	}
}

Start with the PlaceholderResource Feign interface and FeignConfiguration, then compare the concurrent request logs, URLs, and correlation IDs shown in the report. Done means reproducing the cross-request response mix-up and identifying the Feign component or configuration responsible for returning one API call's response to another.