Generator Documentation

This document details the generator structure, which is responsible for importing data from NetBox to Nautobot.

Overview

The implementation is divided into two components: generic and NetBox specific.

Generic Component

The generic component encompasses the NautobotAdapter and SourceAdapter capable of generating DiffSyncModel classes based on the input data, the current version of Nautobot, and any deviations defined in the source configuration.

It comprises the following modules, located in the nautobot_netbox_importer/generator directory:

• base.py: Implements base classes and utilities utilized throughout the application, also establishing constants and shared type definitions.
• nautobot.py: Provides the NautobotAdapter, along with NautobotModelWrapper and NautobotField classes that define the Nautobot structure.
• source.py: Offers the SourceAdapater, SourceModelWrapper and SourceField classes that define the source structure.
• fields.py: Contains factories for fields deviation definitions.
• summary.py: Supplies utility functions for summarizing data structures and presenting import statistics.

NetBox Specific Component

The NetBox specific component is further segmented into sections, located in the nautobot_netbox_importer/diffsync directory:

• adapters/nautobot.py: Inherits NautobotAdapter from the generic NautobotAdapter and implements pieces necessary for SSoT job.
• adapters/netbox.py: Inherits NetBoxAdapter from the generic SourceAdapter and implements the data reader and importer that facilitate the transition from NetBox to Nautobot.
• models/ directory: Contains individual module files that define deviations and field mappings from NetBox to Nautobot.

Stages

The import process consists of the following stages:

Defining a Source Data

The initial step involves creating a SourceAdapter(). It accepts an argument, get_source_data, which is Callable that returns Iterable of the source data items. Each source data item is encapsulated in SourceRecord(content_type: ContentTypeStr, data: Dict) instances. SourceAdapter constructor also passes any additional arguments to its ancestor, the DiffSync class.

The data undergoes two cycles: the first to establish the structure and the second to import the actual data, as described in the following sections.

Defining the Source Structure Deviations

Before importing, it is essential to define any deviations between the source structure and the target Nautobot structure.

This is achieved through adapter.configure_model(content_type: ContentTypeStr). You can specify additional arguments such as:

• nautobot_content_type: Define this when the Nautobot content type differs from the source.
• identifiers: A list of fields identifiable as unique references in the source data.
• default_reference: A RecordData dictionary of default values to reference this model. This is useful when the source data does not provide a reference that is required in Nautobot.
• extend_content_type: Define this when a source model extends another source model to merge into a single Nautobot model.
• forward_references: Define to forward references to another content type. This is useful when the source data references a content type that is not directly related to the Nautobot content type. For example, a source data references a dcim.location content type, but the Nautobot content type is dcim.locationtype.
• disable_related_reference: Define, to disable storing references to this content type to other content types. This is useful for e.g. ObjectChange model.
• pre_import: Define a callable to be executed before importing the source data. Can be used to alter or cache the source data before importing. pre_import(source: RecordData, importer_pass: ImporterPass) -> PreImportResult is called twice for each source record: on first and second input data iteration.
• fields: Define the source fields and how they should be imported. This argument is a dictionary mapping FieldName to SourceFieldDefinition instances.
  • SourceFieldDefinition can be one of:
    • None: to ignore the field.
    • A Nautobot FieldName to map the source field to a Nautobot field.
    • A Callable for specialized field handling.

To disable specific content types, use adapter.disable_model(content_type: ContentTypeStr, reason: str).

Reading Source Structure

The first data iteration constructs the wrapping structure, which includes:

• SourceAdapter with all source model adapter.wrappers.
  • The SourceAdapter manages SourceModelWrapper and NautobotModelWrapper instances.
• A SourceModelWrapper for each source content type, with fields detailing how to import the source data.
  • Each SourceModelWrapper instance corresponds to a single NautobotModelWrapper instance.
• A NautobotModelWrapper for each Nautobot content type, detailing nautobot_wrapper.fields and types, aiding in constructing the DiffSyncModel instances.
  • A single NautobotModelWrapper instance can be referenced by multiple SourceModelWrapper instances.

During this phase, all non-defined but present source fields are appended to the SourceModelWrapper.fields, focusing on field names, not values.

Creating Source Importers

Convert each SourceModelWrapper.fields item into a callable based on previously-established field definitions. The callables convert the source data into the DiffSyncModel constructor's expected structure.

In this stage, the structure described in the previous section is enhanced.

Importing the Data

During this stage, the system performs a second iteration over the input data. This process involves converting the input data into instances of DiffSyncModel by calling the importers defined in the previous step.

Each DiffSyncModel class is dynamically generated as needed. The fields within a DiffSyncModel are defined using nautobot_wrapper.fields. These fields map directly to the attributes of the source data.

For each source record, the importer attempts to read the corresponding Nautobot objects as well, based on the identifiers if they are defined in the source model, or on a generated record's primary key. See Primary Key Generation for more details.

Updating Referenced Content Types

The updating of content_types fields, based on cached references, occurs in this phase. It's possible to define forwarding references using SourceModelWrapper.set_references_forwarding(), e.g. references to dcim.location are forwarded to dcim.locationtype.

Syncing to Nautobot

Data sync to Nautobot is executed using nautobot_adapter.sync_from(source_adapter) from the diffsync library. The object.save() method is used, accommodating objects that fail object.clean(). These objects are verified in the following step.

Validating the Data

After saving all objects, the system verifies the data consistency by re-running clean() on objects that failed during the previous step. All validation errors are collected and can be displayed to the user.

Committing the Transaction

The entire process described above must be encapsulated within a single transaction to ensure atomicity. This approach allows the execution of database statements that may temporarily violate database constraints, with the understanding that these violations will be resolved by the end of the transaction.

If any failure occurs during the process, a rollback is triggered, undoing all changes made during the import process.

ER Diagram

Illustrated below is the ER diagram for the generator structure, created to import data from source to Nautobot.

erDiagram
    DiffSync ||--|| BaseAdapter : "is ancestor"
    BaseAdapter ||--|| SourceAdapter : "is ancestor"
    BaseAdapter ||--|| NautobotAdapter : "is ancestor"
    SourceAdapter ||--o{ SourceModelWrapper : "creates"
    SourceModelWrapper ||--o{ SourceField : "creates"
    SourceAdapter ||--|| NautobotAdapter : "links to"
    NautobotAdapter ||--o{ NautobotModelWrapper : "creates"
    SourceModelWrapper }o--|| NautobotModelWrapper : "links to"
    NautobotModelWrapper ||--o{ NautobotField : "creates"
    NautobotModelWrapper ||--|| NautobotModel : "links to"
    SourceField }o--|| NautobotField : "links to"
    NautobotModelWrapper ||--|| DiffSyncBaseModel : "creates"
    DiffSyncModel ||--o{ DiffSyncBaseModel : "is ancestor"
    SourceAdapter {
        Mapping wrappers
        NautobotAdapter nautobot
        ImportSummary summary
        DiffSyncBaseModel diffsync_model_1
        DiffSyncBaseModel diffsync_model_2
        DiffSyncBaseModel diffsync_model_x
    }
    SourceModelWrapper {
        SourceAdapter adapter
        ContentTypeStr content_type
        NautobotModelWrapper nautobot
        String disable_reason
        Iterable identifiers
        Mapping fields
        Set[Callable] importers
        SourceModelWrapper extends_wrapper
        SourceModelStats stats
        Uid default_reference_uid
        Mapping _uid_to_pk_cache
        Mapping _cached_data
    }
    SourceField {
        SourceModelWrapper wrapper
        FieldName name
        SourceFieldDefinition definition
        NautobotField nautobot
        Callable importer
        String disable_reason
    }
    NautobotAdapter {
        Mapping wrappers
        DiffSyncBaseModel diffsync_model_1
        DiffSyncBaseModel diffsync_model_2
        DiffSyncBaseModel diffsync_model_x
    }
    NautobotModelWrapper {
        ContentTypeStr content_type
        bool disabled
        NautobotBaseModelType model
        NautobotModelStats stats
        Mapping fields
        Type[DiffSyncBaseModel] diffsync_class
        InternalFieldType pk_type
        FieldName pk_name
        Mapping constructor_kwargs
        Int last_id
        Set importer_issues
    }
    NautobotField {
        FieldName name
        InternalFieldType internal_type
        DjangoField field
        Bool disabled
        Bool required
    }
    DiffSyncBaseModel {
        NautobotModelWrapper _wrapper
        Type field_1
        Type field_2
        Type field_x
    }

Other Techniques

• Skipping absent Nautobot models and fields.
• Normalizing datetime values.
• Stabilizing import order.
• Using Nautobot default values to fill in missing source data.
• Auto set-up importers for relation fields.