Spring cloud gateway refresh with RewritePath fails - spring-boot

Question

I'm running a spring cloud gateway instance that relies on spring cloud configuration server. My application starts up with the given following configuration.
cloud:
gateway:
routes:
- id: route-foo
uri: lb://foo
predicates:
- Path=/api/foo/**
filters:
- name: RewritePath
args:
regexp: "/api/foo/(?<remaining>.*)"
replacement: "/${remaining}"
Say I make a modification to my configuration and add an additional route below
- id: route-bar
uri: lb://bar
predicates:
- Path=/api/bar/**
filters:
- name: RewritePath
args:
regexp: "/api/bar/(?<remaining>.*)"
replacement: "/${remaining}"
Executing a POST to http://localhost:8080/actuator/refresh returns the following error.
500 Server Error for HTTP POST "/actuator/refresh" (Encoded)
java.lang.IllegalArgumentException: Could not resolve placeholder 'remaining' in value "/${remaining}"
at org.springframework.util.PropertyPlaceholderHelper.parseStringValue(PropertyPlaceholderHelper.java:178)
It appears that spring is trying to parse my RewritePath replacement and substitute it with environment variables. What are my options?

Answer 1

You're running into spring trying to replace variables in your configuration.
There are two solutions
Escape the replacement syntax (Preferred)
change replacement: "/${remaining}"
to replacement: "/$\\{remaining}"
The RewriteGatewayFilterFactory does a replace on the configuration before running the filter.
Enable ignoreUnresolvableNestedPlaceholders
#Bean
#Primary
public StandardReactiveWebEnvironment standardReactiveWebEnvironmentCustomizer(StandardReactiveWebEnvironment environment) {
environment.setIgnoreUnresolvableNestedPlaceholders(true);
return environment;
}
This will leave all unresolvable placeholders alone in your configuration and not fail during the refresh. I would recommend against this approach as it may end up delaying some issues into runtime if you're relying on a field to be populated correctly.
Theoretically you should be able to accomplish this same functionality with the PropertySourcesPlaceholderConfigurer, I had a hard time getting that to cooperate.