Fix redpanda_migrator_bundle output template

The output needs to know what custom label was set for the
redpanda_migrator_bundle input, if any. Otherwise, it can't
find the input components it needs to talk to.

Signed-off-by: Mihai Todor <mihai.todor@contractor.redpanda.com>

Author: mihaitodor

CHANGELOG.md

@@ -3,6 +3,12 @@ Changelog
 
 All notable changes to this project will be documented in this file.
 
+## 4.56.0 - TBD
+
+### Added
+
+- Field `input_bundle_label` added to the `redpanda_migrator_bundle` output. (@mihaitodor)
+
 ## 4.55.1 - 2025-05-19
 
 ### Added

docs/modules/components/pages/outputs/redpanda_migrator_bundle.adoc

@@ -33,6 +33,7 @@ output:
     redpanda_migrator: {} # No default (required)
     schema_registry: {} # No default (required)
     translate_schema_ids: false
+    input_bundle_label: ""
 ```
 
 All-in-one output which writes messages and schemas to a Kafka or Redpanda cluster. This output is meant to be used
@@ -67,4 +68,13 @@ when it already contains some schemas which differ from the ones being migrated.
 
 *Default*: `false`
 
+=== `input_bundle_label`
+
+Specify the redpanda_migrator_bundle input label if one is assigned to it.
+
+
+*Type*: `string`
+
+*Default*: `""`
+
 

internal/impl/kafka/input_redpanda_migrator_bundle.tmpl.yaml

@@ -46,7 +46,7 @@ mapping: |
 
   let labelPrefix = @label.not_empty().or("redpanda_migrator_bundle")
 
-  let redpandaMigrator = this.redpanda_migrator.assign({"output_resource": "%s_redpanda_migrator_output".format($labelPrefix)})
+  let redpandaMigrator = this.redpanda_migrator
 
   let redpandaMigratorOffsets = this.redpanda_migrator.with("seed_brokers", "topics", "regexp_topics", "consumer_group", "topic_lag_refresh_period", "client_id", "rack_id", "tls", "sasl")
 
@@ -155,7 +155,6 @@ tests:
               seed_brokers: [ "127.0.0.1:9092" ]
               topics: [ "foobar" ]
               consumer_group: "migrator"
-              output_resource: redpanda_migrator_bundle_redpanda_migrator_output
             processors:
               - mapping: meta input_label = "redpanda_migrator_input"
           - label: redpanda_migrator_bundle_redpanda_migrator_offsets_input
@@ -199,7 +198,6 @@ tests:
                     seed_brokers: [ "127.0.0.1:9092" ]
                     topics: [ "foobar" ]
                     consumer_group: "migrator"
-                    output_resource: redpanda_migrator_bundle_redpanda_migrator_output
                   processors:
                     - mapping: meta input_label = "redpanda_migrator_input"
                 - label: redpanda_migrator_bundle_redpanda_migrator_offsets_input
@@ -225,7 +223,6 @@ tests:
               seed_brokers: [ "127.0.0.1:9092" ]
               topics: [ "foobar" ]
               consumer_group: "migrator"
-              output_resource: redpanda_migrator_bundle_redpanda_migrator_output
             processors:
               - mapping: meta input_label = "redpanda_migrator_input"
           - label: redpanda_migrator_bundle_redpanda_migrator_offsets_input

internal/impl/kafka/output_redpanda_migrator_bundle.tmpl.yaml

@@ -44,10 +44,18 @@ fields:
       Allow the target Schema Registry instance to allocate different schema IDs for migrated schemas. This is useful
       when it already contains some schemas which differ from the ones being migrated.
 
+  - name: input_bundle_label
+    type: string
+    kind: scalar
+    default: ""
+    description: |
+      Specify the redpanda_migrator_bundle input label if one is assigned to it.
+
 mapping: |
   #!blobl
 
   let labelPrefix = @label.not_empty().or("redpanda_migrator_bundle")
+  let inputBundleLabel = this.input_bundle_label.not_empty().or("redpanda_migrator_bundle")
 
   if this.translate_schema_ids == true && this.schema_registry.length() == 0 {
     root = throw("Schema ID translation requires schema_registry to be configured")
@@ -75,7 +83,7 @@ mapping: |
         ]
       },
       "translate_schema_ids": this.translate_schema_ids.or(false),
-      "input_resource": "%s_redpanda_migrator_input".format($labelPrefix)
+      "input_resource": "%s_redpanda_migrator_input".format($inputBundleLabel)
     }
   )
 
@@ -100,7 +108,7 @@ mapping: |
     this.schema_registry.assign({
       "subject": "${! @schema_registry_subject }",
       "max_in_flight": $srMaxInFlight,
-      "input_resource": "%s_schema_registry_input".format($labelPrefix),
+      "input_resource": "%s_schema_registry_input".format($inputBundleLabel),
       "translate_ids": this.translate_schema_ids.or(false)
     })
   }
@@ -225,6 +233,71 @@ tests:
                       - output:
                           reject: ${! @fallback_error }
 
+  - name: Migrate messages, offsets and schemas when setting a label on the bundle input
+    config:
+      redpanda_migrator:
+        seed_brokers: [ "127.0.0.1:9092" ]
+        topic_prefix: dest.
+        max_in_flight: 1
+      schema_registry:
+        url: http://localhost:8081
+        max_in_flight: 1
+      input_bundle_label: source
+
+    expected:
+      switch:
+        cases:
+          - check: metadata("input_label") == "redpanda_migrator_input"
+            output:
+              label: redpanda_migrator_bundle_redpanda_migrator_output
+              redpanda_migrator:
+                key: ${! metadata("kafka_key") }
+                max_in_flight: 1
+                partition: ${! metadata("kafka_partition").or(throw("missing kafka_partition metadata")) }
+                partitioner: manual
+                seed_brokers:
+                  - 127.0.0.1:9092
+                timestamp_ms: ${! metadata("kafka_timestamp_ms").or(timestamp_unix_milli()) }
+                topic: ${! metadata("kafka_topic").or(throw("missing kafka_topic metadata")) }
+                topic_prefix: "dest."
+                metadata:
+                  include_patterns:
+                    -  ^(?:[^k].*|k[^a].*|ka[^f].*|kaf[^k].*|kafk[^a].*|kafka[^_].*)
+                translate_schema_ids: false
+                input_resource: source_redpanda_migrator_input
+                schema_registry_output_resource: redpanda_migrator_bundle_schema_registry_output
+              processors:
+                - mapping: |
+                    meta input_label = deleted()
+          - check: metadata("input_label") == "redpanda_migrator_offsets_input"
+            output:
+              label: redpanda_migrator_bundle_redpanda_migrator_offsets_output
+              redpanda_migrator_offsets:
+                seed_brokers:
+                  - 127.0.0.1:9092
+                offset_topic_prefix: "dest."
+          - check: metadata("input_label") == "schema_registry_input"
+            output:
+              fallback:
+                - label: redpanda_migrator_bundle_schema_registry_output
+                  schema_registry:
+                    subject: ${! @schema_registry_subject }
+                    url: http://localhost:8081
+                    max_in_flight: 1
+                    translate_ids: false
+                    input_resource: source_schema_registry_input
+                - switch:
+                    cases:
+                      - check: '@fallback_error == "request returned status: 422"'
+                        output:
+                          drop: {}
+                          processors:
+                            - log:
+                                message: |
+                                  Subject '${! @schema_registry_subject }' version ${! @schema_registry_version } already has schema: ${! content() }
+                      - output:
+                          reject: ${! @fallback_error }
+
   - name: Migrate messages, offsets and schemas with schema ID translation
     config:
       redpanda_migrator: