Throw an error when replenishRate > burstCapacity

Fixes gh-2453

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/filter/ratelimit/RedisRateLimiter.java

@@ -40,6 +40,7 @@ import org.springframework.context.ApplicationContextAware;
 import org.springframework.core.style.ToStringCreator;
 import org.springframework.data.redis.core.ReactiveStringRedisTemplate;
 import org.springframework.data.redis.core.script.RedisScript;
+import org.springframework.util.Assert;
 import org.springframework.validation.annotation.Validated;
 
 /**
@@ -335,6 +336,8 @@ public class RedisRateLimiter extends AbstractRateLimiter<RedisRateLimiter.Confi
 		}
 
 		public Config setBurstCapacity(int burstCapacity) {
+			Assert.isTrue(burstCapacity >= this.replenishRate, "BurstCapacity(" + burstCapacity
+					+ ") must be greater than or equal than replenishRate(" + this.replenishRate + ")");
 			this.burstCapacity = burstCapacity;
 			return this;
 		}

spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/filter/ratelimit/RedisRateLimiterConfigTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.cloud.gateway.filter.ratelimit;
 
+import org.assertj.core.api.Assertions;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -55,6 +56,11 @@ public class RedisRateLimiterConfigTests {
 		routeLocator.getRoutes().collectList().block();
 	}
 
+	@Test
+	public void shouldThrowAnErrorWhenReplenishRateIsHigherThanBurstCapacity() {
+		Assertions.assertThatThrownBy(() -> new RedisRateLimiter(10, 5)).isInstanceOf(IllegalArgumentException.class);
+	}
+
 	@Test
 	public void redisRateConfiguredFromEnvironment() {
 		assertFilter("redis_rate_limiter_config_test", 10, 20, 1, false);