Add a README

Author: poojanilangekar

extensions/federation/README.md

@@ -0,0 +1,9 @@
+### Using the `HadoopFederatedCatalogFactory`
+
+This module is an independent compilation unit and will be built into the Polaris binary only when the following flag is set in gradle.properties or as a JVM arg at compile time:
+
+```
+NonRESTCatalogs=HADOOP,<alternates>
+```
+
+Without this flag, the Hadoop factory won't be compiled into Polaris and therefore Polaris will not load the class at runtime, throwing an unsupported exception for federated catalog calls.

runtime/server/build.gradle.kts

@@ -49,6 +49,10 @@ dependencies {
   runtimeOnly(project(":polaris-relational-jdbc"))
   runtimeOnly("io.quarkus:quarkus-jdbc-postgresql")
 
+  if ((project.findProperty("NonRESTCatalogs") as String?)?.contains("HADOOP") == true) {
+    runtimeOnly(project(":polaris-extensions-federation-hadoop"))
+  }
+
   // enforce the Quarkus _platform_ here, to get a consistent and validated set of dependencies
   implementation(enforcedPlatform(libs.quarkus.bom))
   implementation("io.quarkus:quarkus-container-image-docker")

runtime/service/build.gradle.kts

@@ -30,9 +30,6 @@ dependencies {
   implementation(project(":polaris-api-management-service"))
   implementation(project(":polaris-api-iceberg-service"))
   implementation(project(":polaris-api-catalog-service"))
-  if ((project.findProperty("NonRESTCatalogs") as String?)?.contains("HADOOP") == true) {
-    runtimeOnly(project(":polaris-extensions-federation-hadoop"))
-  }
 
   runtimeOnly(project(":polaris-relational-jdbc"))