Retaining the Request's Path During Spring Cloud Gateway Failover - spring

Question

Is there a way to externally configure Spring Cloud Gateway to failover to another data center? I'm thinking of something like this:
spring:
cloud:
gateway:
routes:
- id: test-service
uri: lb://test-service:8085/
predicates:
- Path=/test-service/**
filters:
- StripPrefix=1
- name: CircuitBreaker
args:
name: fallback
fallbackUri: forward:/fallback
#fallbackUri: forward:/fallback/test-service
- id: fallback
uri: http://${fallback_data_center}
predicates:
- Path=/fallback/**
---
spring:
config:
activate:
on-profile: data_center_1
fallback_data_center: dc2.com
---
spring:
config:
activate:
on-profile: data_center_2
fallback_data_center: dc1.com
The problem I run into is that the CircuitBreaker filter's fallbackUri parameter only supports forward schemed URIs. However, the path part of the request URL is overridden with the path in the forward URL. So there does not appear to be a way to failover with the path from the original request such as if this configuration had received a request of http://dc1.com/test-service/some/path without creating a configuration for every possible path.

Answer 1

At the time of writing this answer there is still now official way of doing a failover to another host.
What we are trying to achieve in our team is to have routes with Retry and CircuitBreaker filters which can fallback to another host keeping the original request unmodified ( request payload, header, query params and most importantly the API context path ) and just replacing the host so we can fallback to another datacenter.
We archived this by using the default Gateway Retry and CircuitBreaker filters and developing a custom FallbackController which just replaces the host with a configured property and keeps the rest of the request unmodified including the request context path:
#RestController
#RequestMapping("/fallback")
#ConditionalOnProperty(value="gateway.fallback.enabled", havingValue = "true")
public class FallbackController {
private final GatewayFallbackConfig gatewayFallbackConfig;
private final WebClient webClient;
public FallbackController(GatewayFallbackConfig gatewayFallbackConfig) {
this.gatewayFallbackConfig = gatewayFallbackConfig;
this.webClient = WebClient.create();
}
#PostMapping
Mono<ResponseEntity<String>> postFallback(#RequestBody(required = false) String body,
ServerWebExchangeDecorator serverWebExchangeDecorator) {
return fallback(body, serverWebExchangeDecorator);
}
#GetMapping
Mono<ResponseEntity<String>> getFallback(#RequestBody(required = false) String body,
ServerWebExchangeDecorator serverWebExchangeDecorator) {
return fallback(body, serverWebExchangeDecorator);
}
#PatchMapping
Mono<ResponseEntity<String>> patchFallback(#RequestBody(required = false) String body,
ServerWebExchangeDecorator serverWebExchangeDecorator) {
return fallback(body, serverWebExchangeDecorator);
}
#DeleteMapping
Mono<ResponseEntity<String>> deleteFallback(#RequestBody(required = false) String body,
ServerWebExchangeDecorator serverWebExchangeDecorator) {
return fallback(body, serverWebExchangeDecorator);
}
private Mono<ResponseEntity<String>> fallback(String body, ServerWebExchangeDecorator serverWebExchangeDecorator) {
ServerHttpRequest originalRequest = serverWebExchangeDecorator.getDelegate().getRequest();
WebClient.RequestBodySpec request = webClient.method(originalRequest.getMethod())
.uri(buildFallbackURI(originalRequest));
Optional.ofNullable(body)
.ifPresent(request::bodyValue);
return request.exchangeToMono(response -> response.toEntity(String.class));
}
private URI buildFallbackURI(ServerHttpRequest originalRequest) {
return UriComponentsBuilder.fromHttpRequest(originalRequest)
.scheme(gatewayFallbackConfig.getScheme())
.host(gatewayFallbackConfig.getHost())
.port(gatewayFallbackConfig.getPort())
.build(ServerWebExchangeUtils.containsEncodedParts(originalRequest.getURI()))
.toUri();
}
With an additional property configuration holder:
#Getter
#Component
#RefreshScope
#ConditionalOnProperty(value="gateway.fallback.enabled", havingValue = "true")
public class GatewayFallbackConfig {
private final String scheme;
private final String host;
private final String port;
private final Set<String> excludedHeaders;
public GatewayFallbackConfig(
#Value("${gateway.fallback.scheme:https}") String scheme,
#Value("${gateway.fallback.host}") String host,
#Value("${gateway.fallback.port:#{null}}") String port,
#Value("${gateway.fallback.headers.exclude}") Set<String> excludedHeaders) {
this.scheme = scheme;
this.host = host;
this.port = port;
this.excludedHeaders = excludedHeaders;
}
And we are using it with a route configuration like that:
- id: example-route
uri: http://localhost:8080
predicates:
- Path=/foo/bar/**
filters:
- name: CircuitBreaker
args:
name: exampleCircuitBreaker
fallbackUri: forward:/fallback
statusCodes:
- INTERNAL_SERVER_ERROR
- BAD_GATEWAY
- SERVICE_UNAVAILABLE
- name: Retry
args:
retries: 3
statuses: BAD_GATEWAY,SERVICE_UNAVAILABLE,GATEWAY_TIMEOUT
series: SERVER_ERROR
methods: GET,POST,PUT,DELETE
exceptions: org.springframework.cloud.gateway.support.NotFoundException,javax.security.auth.login.LoginException
backoff:
firstBackoff: 10ms
maxBackoff: 50ms
factor: 2
basedOnPreviousValue: false
gateway:
fallback:
scheme: https
host: some.other.host.com
enabled: true