# Backend module

A backend module is a self-contained unit of backend functionality tied to a specific n8n feature.

Benefits of modularity:

- **Organization:** Keep code structured, focused and discoverable
- **Independence**: Reduce conflicts among teams working independently
- **Decoupling**: Prevent features from becoming entangled with internals
- **Simplicity:** Make logic easier to maintain, test and reason about
- **Efficiency**: Load and run only modules that are explicitly enabled

## File structure

To set up a backend module, run this command at monorepo root:

```sh
pnpm setup-backend-module
```

Your new module will be located at `packages/cli/src/modules/my-feature`. Rename `my-feature` in the dirname and in the filenames to your actual feature name. Use kebab-case.

A module’s file structure is as follows:

```sh
.
├── __tests__
│   ├── my-feature.controller.test.ts
│   └── my-feature.service.test.ts
├── my-feature.entity.ts            # DB model
├── my-feature.repository.ts        # DB access
├── my-feature.config.ts            # env vars
├── my-feature.constants.ts         # constants
├── my-feature.controller.ts        # HTTP REST routes
├── my-feature.service.ts           # business logic
└── my-feature.module.ts            # entrypoint
```

This is only a template - your module may not need all of these files, or it may need more than these and also subdirs to keep things organized. Infixes are currently not required (except for the `.module.ts` entrypoint), but infixes are strongly recommended as they make the contents searchable and discoverable.

Backend modules currently live at `packages/cli/src/modules`, so imports can be:

- from inside the module dir
- from common packages like `@n8n/db`, `@n8n/backend-common`, `@n8n/backend-test-utils`, etc.
- from `cli`
- from third-party libs available in, or added to, `cli`

Modules are managed via env vars:

- To enable a module (activate it on instance startup), use the env var `N8N_ENABLED_MODULES`.
- To disable a module (skip it on instance startup), use the env var `N8N_DISABLED_MODULES`.
- Some modules are **default modules** so they are always enabled unless specifically disabled. To enable a module by default, add it [here](https://github.com/n8n-io/n8n/blob/c0360e52afe9db37d4dd6e00955fa42b0c851904/packages/%40n8n/backend-common/src/modules/module-registry.ts#L26).

Modules that are under a license flag are automatically skipped on startup if the instance is not licensed to use the feature.

## Entrypoint

The `.module.ts` file is the entrypoint of the module and uses the `@BackendModule()` decorator:

```ts
@BackendModule({ name: 'my-feature' })
export class MyFeatureModule implements ModuleInterface {
  async init() {
    await import('./my-feature.controller');

    const { MyFeatureService } = await import('./my-feature.service');

    Container.get(MyFeatureService).start();
  }

  @OnShutdown()
  async shutdown() {
    const { MyFeatureService } = await import('./my-feature.service');

    await Container.get(MyFeatureService).shutdown();
  }

  async entities() {
    const { MyEntity } = await import('./my-feature.entity.ts');
    return [MyEntity]
  }

  async settings() {
    const { MyFeatureService } = await import('./my-feature.service');

    return Container.get(MyFeatureService).settings();
  }

  async context() {
    const { MyFeatureService } = await import('./my-feature.service');

    return { myFeatureProxy: Container.get(MyFeatureService) };
  }
}
```

The entrypoint is responsible for providing:

- **initialization logic**, e.g. in insights, start compaction timers,
- **shutdown logic**, e.g. in insights, stop compaction timers,
- **database entities** to register with `typeorm`, e.g. in insights, the three database entities `InsightsMetadata`, `InsightsByPeriod` and `InsightsRaw`
- **settings** to send to the client for adjusting the UI, e.g. in insights, `{ summary: true, dashboard: false }`
- **context** to merge an object into the workflow execution context `WorkflowExecuteAdditionalData`. This allows you to make module functionality available to `core`, namespaced under the module name. For now, you will also need to manually [update the type](https://github.com/n8n-io/n8n/blob/master/packages/core/src/execution-engine/index.ts#L7) of `WorkflowExecuteAdditionalData` to reflect the resulting context.

A module entrypoint may or may not need to implement all of these methods.

Why do we use dynamic imports in entrypoint methods? `await import('...')` ensures we load module-specific logic **only when needed**, so that n8n instances which do not have a module enabled, or do not have licensed access to it, do not pay for the performance cost. Linting enforces that relative imports in the entrypoint use dynamic imports. Loading on demand is also the reason why the entrypoint does not use dependency injection, and forbids it via linting.

A module may be fully behind a license flag:

```ts
@BackendModule({
  name: 'external-secrets',
  licenseFlag: 'feat:externalSecrets'
})
export class ExternalSecretsModule implements ModuleInterface {
  // This module will be activated only if the license flag is true.
}
```

If a module is only _partially_ behind a license flag, e.g. insights, then use the `@Licensed()` decorator instead:

```ts
class InsightsController {
  constructor(private readonly insightsService: InsightsService) {}

  @Get('/by-workflow')
  @Licensed('feat:insights:viewDashboard')
  async getInsightsByWorkflow(
    _req: AuthenticatedRequest,
    _res: Response,
    @Query payload: ListInsightsWorkflowQueryDto,
  ) {
    const dateRangeAndMaxAgeInDays = this.getMaxAgeInDaysAndGranularity({
      dateRange: payload.dateRange ?? 'week',
    });
    return await this.insightsService.getInsightsByWorkflow({
      maxAgeInDays: dateRangeAndMaxAgeInDays.maxAgeInDays,
      skip: payload.skip,
      take: payload.take,
      sortBy: payload.sortBy,
    });
  }
}
```

Module-level decorators to be aware of:

- `@OnShutdown()` to register a method to be called during the instance shutdown sequence

## Controller

To register a controller with the server, simply import the controller file in the module entrypoint: 

```ts
@BackendModule({ name: 'my-feature' })
export class MyFeatureModule implements ModuleInterface {
  async init() {
    await import('./my-feature.controller');
  }
}
```

A controller must handle only request-response orchestration, delegating business logic to services.

```ts
@RestController('/my-feature')
export class MyFeatureController {
  constructor(private readonly myFeatureService: MyFeatureService) {}

  @Get('/summary')
  async getSummary(_req: AuthenticatedRequest, _res: Response) {
    return await this.myFeatureService.getSummary();
  }
}
```

Controller-level decorators to be aware of:

- `@RestController()` to define a REST controller
- `@Get()`, `@Post()`, `@Put()`, etc. to define controller routes
- `@Query()`, `@Body()`, etc. to validate requests
- `@GlobalScope()` to gate a method depending on a user's instance-wide permissions
- `@ProjectScope()` to gate a method depending on a user's project-specific permissions
- `@Licensed()` to gate a method depending on license state

## Services

Services handle business logic, delegating database access to repositories.

To kickstart a service during module init, run the relevant method in the module entrypoint:

```ts
@BackendModule({ name: 'my-feature' })
export class MyFeatureModule implements ModuleInterface {
  async init() {
    const { MyFeatureService } = await import('./my-feature.service');
    Container.get(MyFeatureService).start();
  }
}
```

A module typically has one service, but it may have as many as needed.

```ts
@Service()
export class MyFeatureService {
  private intervalId?: NodeJS.Timeout;

  constructor(
    private readonly myFeatureRepository: MyFeatureRepository,
    private readonly logger: Logger,
    private readonly config: MyFeatureConfig,
  ) {
    this.logger = this.logger.scoped('my-feature');
  }

  start() {
    this.logger.debug('Starting feature work...');

    this.intervalId = setInterval(
      () => {
        this.logger.debug('Running scheduled task...');
      },
      this.config.taskInterval * 60 * 1000,
    );
  }
```

Service-level decorators to be aware of:

- `@Service()` to make a service usable by the dependency injection container
- `@OnLifecycleEvent()` to register a class method to be called on an execution lifecycle event, e.g. `nodeExecuteBefore`, `nodeExecuteAfter`, `workflowExecuteBefore`, and `workflowExecuteAfter`
- `@OnPubSubEvent()` to register a class method to be called on receiving a message via Redis pubsub
- `@OnLeaderTakeover()` and `@OnLeaderStepdown` to register a class method to be called on leadership transition in a multi-main setup

## Repositories

Repositories handle database access using `typeorm`, operating on database models ("entities").

```ts
@Service()
export class MyFeatureRepository extends Repository<MyFeatureEntity> {
  constructor(dataSource: DataSource) {
    super(MyFeatureEntity, dataSource.manager);
  }

  async getSummary() {
    return await /* typeorm query on entities */; 
  }
}
```

Repository-level decorators to be aware of:

- `@Service()` to make a repository usable by the dependency injection container

## Entities

Entities are database models, typically representing tables in the database.

```ts
@Entity()
export class MyFeatureEntity extends BaseEntity {
  @Column()
  name: string;

  @Column()
  count: number;
}
```

We recommend using the `.entity.ts` infix, but omit the `-Entity` suffix from the class name to make it less verbose. (The `-Entity` suffix is being used in the setup example only for consistency with other placeholders.)

Entities must be registered with `typeorm` in the module entrypoint:

```ts
class MyFeatureModule implements ModuleInterface {
  async entities() {
    const { MyFeatureEntity } = await import('./my-feature.entity');
    
    return [MyFeatureEntity];
  }
}
```

Entity-level decorators to be aware of:

- `@Entity()` to define an entity

## Migrations

As an exception, migrations remain centralized at `@n8n/db/src/migrations`, because conditionally running migrations would introduce unwanted complexity at this time. This means that schema changes from modules are _always_ applied to the database, even when modules are disabled.

## Configuration

Module-specific configuration is defined in the the `.config.ts` file:

```ts
@Config
export class MyFeatureConfig {
  /**
   * How often in minutes to run some task.
   * @default 30
   */
  @Env('N8N_MY_FEATURE_TASK_INTERVAL')
  taskInterval: number = 30;
}
```

Config-level decorators to be aware of:

- `@Env()` to define environment variables
- `@Config()` to register a config class and make it usable by the dependency injection container

## CLI commands

Occasionally, a module may need to define a module-specific CLI command. To do so, set up a `.command.ts` file and use the `@Command()` decorator. Currently there are no module-specific commands, so use any of the existing global CLI commands at `packages/cli/src/commands` as reference.

## Tests

Place unit and integration tests for a backend module at `packages/cli/src/modules/{featureName}/__tests__`. Use the `.test.ts` infix.

Currently, testing utilities live partly at `cli` and partly at `@n8n/backend-test-utils`. In future, all testing utilities will be moved to common packages, to make modules more decoupled from `cli`.

## Future work

1. A few aspects of modules continue to be defined outside a module's dir:

- Add a license flag to `LICENSE_FEATURES` at `packages/@n8n/constants/src/index.ts`
- Add a logging scope to `LOG_SCOPES` at `packages/cli/src/logging.config.ts`
- Add a license check to `LicenseState` at `packages/@n8n/backend-common/src/license-state.ts`
- Add a migration (as discussed above) at `packages/@n8n/db/src/migrations`
- Add request payload validation using `zod` at `@n8n/api-types`
- Add a module to default modules at `packages/@n8n/backend-common/src/modules/module-registry.ts`

2. License events (e.g. expiration) currently do not trigger module shutdown or initialization at runtime.

3. Some core functionality is yet to be moved from `cli` into common packages. This is not a blocker for module adoption, but this is desirable so that (a) modules become decoupled from `cli` in the long term, and (b) future external extensions can access some of that functionality. 

4. Existing features that are not modules (e.g. LDAP) should be turned into modules over time.

## FAQs

- **What is a good example of a backend module?** Our first backend module is the `insights` module at `packages/@n8n/modules/insights`.
- **My feature is already a separate _package_ at `packages/@n8n/{feature}`. How does this work with modules?** If your feature is already fully decoupled from `cli`, or if you know in advance that your feature will have zero dependencies on `cli`, then you already stand to gain most of the benefits of modularity. In this case, you can add a thin module to `cli` containing an entrypoint to your feature imported from your package, so that your feature is loaded only when needed.
- **Does all new functionality need to be added as a module?** If your feature relies heavily on internals, e.g. workflow archival, then a module may not be a good fit. Consider a module first, but use your best judgment. Reach out if unsure.
- **Are backend modules meant for use by external contributors?** No, they are meant for features developed by the core team.
- **How do I hot reload a module?** Modules are part of `cli` so you can use the usual `watch` command.
- **How do modules interoperate with each other?** This is not supported at this time. Reach out if you need this.
- **I have a use case that is not covered by modules. What should I do?** Modules live in `cli` so any imports from `cli` remain available, i.e. aim for decoupling but do not consider it a blocker for progress. Reach out if you think the module system needs expanding.
