Fix validation for default route

Signed-off-by: Taylor Gray <tylgry@amazon.com>

Author: graytaylor0

data-prepper-core/src/integrationTest/resources/org/opensearch/dataprepper/pipeline/route/three-route-with-default-route.yaml

@@ -13,7 +13,6 @@ routing-pipeline:
     - alpha: '/value == "a"'
     - beta: '/value == "b"'
     - gamma: '/value == "g"'
-    - _default: '/_default == "z"'
   sink:
     - in_memory:
         testing_key: ConditionalRoutingIT_alpha

data-prepper-pipeline-parser/src/main/java/org/opensearch/dataprepper/pipeline/parser/PipelineConfigurationValidator.java

@@ -30,6 +30,8 @@ public class PipelineConfigurationValidator {
     private static final String PIPELINE_TYPE = "pipeline";
     private static final Set<String> INVALID_PIPELINE_NAMES = new HashSet<>(List.of("data-prepper", "dataPrepper", "core"));
 
+    private static final String DEFAULT_ROUTE = "_default";
+
     /**
      * Sorts the pipelines in topological order while also validating for
      * i. cycles in pipeline configuration
@@ -199,6 +201,7 @@ private static void validateSinkRoutes(final Map<String, PipelineConfiguration>
                 }
                 List<String> invalidRoutes = sinkRoutes.stream()
                         .filter(route -> !validRoutes.contains(route))
+                        .filter(route -> !route.equals(DEFAULT_ROUTE))
                         .collect(Collectors.toList());
 
                 if (!invalidRoutes.isEmpty()) {