Migrating components using a template with variables

Learn how to use the Cloudera Flow Management Migration Tool to migrate components from flow definition JSON files. As templates may not contain some parameter contexts and parameters defined at the parent process group level, you have to use the flow definitions generated in the previous steps.

Example flow for migrating components

The following NiFi flow is used to demonstrate both variable and component migration.

There is one flow definition file from the variable migration step:

TCP_Listener_template.json
The file consists of the process group TCP Listener (ID: b41940d7-0194-1000-42fc-458834630567).

TCP Listener Process Group

This process group contains the following simple flow:

The process group defines a variable called TCP Listener Port, which is referenced by the ListenTCPRecord processor.

The example guides you through component migration and maintaining a clear activity log. While this example flow definition is simple, the step-by-step approach shows how this method improves clarity for more complex migrations. In real-world scenarios, you have to define a migration strategy based on your flow’s structure.

Use the flow definition file in the /etc/migration-tool-input from step 3.

This is a NiFi-1 compatible flow definition that no longer contains variables.
Run Stage 1 component migration on the TCP_Listener_template.json process group using the following command.
```
bin/migration.sh nifi migrate-components \
-i /etc/migration-tool-input/TCP_Listener_template.json \
-od /etc/migration-tool-output/components \
--sourceCompatibleOutput
```
This generates a sourceVersion folder that contains the output files of the Stage 1 migration.
```
components
└── sourceVersion
    ├── activity_log.json
    └── migrated_output
        └── migrated_TCP_Listener_template.json
```
activity_log.json
- The log describes all the actions that were performed for this stage of the process group migration.
- Log of all actions performed during this stage of the process group migration.
migrated_TCP_Listener_template.json
- A modified NiFi 1 flow, which is not compatible with NiFi 2 yet.
- It contains everything the original flow did, except the TCP Listener process group was modified as described in the Activity Log.
Validate the Stage 1 component migration output for migrated_TCP_Listener_template.json.
1. Load the migrated_TCP_Listener_template.json into a NiFi 1 instance and check the flow.
2. Review the activity_log.json file and check for any manual-change-requests ormanual-validation-requests. If none are present, proceed to the next step.
  In this example, you can see the following information in the activity log:
```
{
	"sequence" : 2,
	"type" : "change-info",
	"subject" : "b41966ad-0194-1000-a08d-a92489457356",
	"message" : "Component [org.apache.nifi.processors.standard.ListenTCPRecord] has been deprecated (NIFI-13509)",
	"context" : {
  	"rule" : "36227b60-75f0-40dc-8caf-a2ec577aa54c"
}
```
  1. 1. Open the targetVersion/migrated_TCP_Listener_template.json file and search for the "subject" ID, b41966ad-0194-1000-a08d-a92489457356. This ID refers to the ListenTCPRecord processor.
    2. Search for the value of the identifier as “subject” element in NiFi’s search box.
      
      You are directed to the ListenTCPRecord processor. No manual modifications are needed at this stage. However, it is important to note that the ListenTCPRecord processor is deprecated and is not available in NiFi 2. Once the full component migration (Stage 1 and Stage 2) is complete, instructions will be provided on how to handle this deprecation.
3. If manual changes are necessary, update the migrated_TCP_Listener_template.json on the NiFi canvas after loading it. Once the flow is validated and meets expectations, continue with the next step.
At this stage, you have completed Stage 1 of both variable and component migration for your flow definition file. After reviewing the logs, you confirmed that no manual changes were needed. You can proceed with a full component migration using the /etc/migration-tool-input from Step 3.
Run full component migration (Stage 1 and 2) for TCP_Listener_template.json.
1. Make a backup of the output folder (/etc/migration-tool-output/components) before running the next migration step.
  
  note
  
  This step is crucial because the same output folder is used as in the previous migration, and its contents will be overwritten. To retain a record of changes made at each stage, it is better to create a backup.
2. Run the full component migration using the following command.
```
bin/migration.sh nifi migrate-components \
-i /etc/migration-tool-input/TCP_Listener_template.json \
-od /etc/migration-tool-output/components
```
  This generates the following output:
```
components
├── sourceVersion
│   ├── activity_log.json
│   └── migrated_output
│	└── migrated_TCP_Listener_template.json
└── targetVersion
    ├── activity_log.json
    └── migrated_output
	└── migrated_TCP_Listener_template.json
```
  The contents of the previously generated sourceVersion folder will be overwritten. The contents represent the NiFi 1-compatible version of the migrated flow. Since the root process group only contained the two process groups on which you already performed Stage 1 component migration, the activity log will only include the same entries as those in Steps 2 and 4.
  
  Additionally, a targetVersion directory is created, containing the output files of the Stage 2 part of the migration:
  migrated_TCP_Listener_template.json
  NiFi 2-compatible flow in terms of variables
  
  You can load it into NiFi 2 and validate it
  activity_log.json
  List of all actions performed during this stage of the migration, and any manual steps that you need to perform.
Validate the Stage 2 component migration output for migrated_TCP_Listener_template.json.
1. Load the targetVersion/migrated_output/migrated_TCP_Listener_template.json into a NiFi 2 instance and check the flow.
2. Review the targetVersion/activity_log.json file.
  In this example, you can see the following manual-change-request entry.
```
{
	"sequence" : 6,
	"type" : "manual-change-request",
	"subject" : "b41966ad-0194-1000-a08d-a92489457356",
	"message" : "The component has been deprecated. It is suggested to replace it with a combination of [org.apache.nifi.processors.standard.ListenTCP] and [org.apache.nifi.processors.standard.ConvertRecord] processors",
	"context" : {
  	"rule" : "36227b60-75f0-40dc-8caf-a2ec577aa54c"
}
```
  1. Open the targetVersion/migrated_TCP_Listener_template.json file and search for the "subject" ID, b41966ad-0194-1000-a08d-a92489457356. This ID refers to the ListenTCPRecord processor.
  2. To identify the processor affected by these changes, search for the identifier value of the “subject” element in NiFi’s search box. It refers to the ListenTCPRecord processor.
  3. Open the TCP Listener process group. You can see that the processor is marked with dashed borders and its version number still shows that of the NiFi 1 instance. It means that it is a "ghost processor", not available in NiFi 2. The log message suggests replacing it with a combination of ListenTCP and ConvertRecord processors.
  4. Instantiate and configure the ListenTCP and ConvertRecord processors, connect them appropriately, and then remove the ghost processor.
    
    Besides these changes there are no further manual-change-requests or manual-validation-requests in the activity log.
3. Download the flow definition and you have the fully NiFi 2 compatible TCP_Listener_template.json.