# ITopicConfig

**Kind:** Interface

**Source:** [`packages/microservices/external/kafka.interface.ts`](https://github.com/nestjs/nest/blob/master/packages/microservices/external/kafka.interface.ts#L266)

**Part of:** [Microservices](subsystem-packages-microservices)

`ITopicConfig` defines the configuration required to create or manage a Kafka topic in the microservices integration layer. It specifies the topic name, partitioning and replication settings, optional replica placement, and broker-level topic configuration entries.

## Properties

| Property | Type |
|---|---|
| `topic` | `string` |
| `numPartitions` | `number` |
| `replicationFactor` | `number` |
| `replicaAssignment` | `object[]` |
| `configEntries` | `IResourceConfigEntry[]` |

## Diagram

```mermaid
graph LR
  A[ITopicConfig] --> B[topic: string]
  A --> C[numPartitions: number]
  A --> D[replicationFactor: number]
  A --> E[replicaAssignment: object[]]
  A --> F[configEntries: IResourceConfigEntry[]]

  C --> G[Kafka partitions]
  D --> H[Replica count]
  E --> I[Explicit broker assignment]
  F --> J[Topic-level broker settings]
```

## Usage

```ts
import type { ITopicConfig } from './kafka.interface';

const topicConfig: ITopicConfig = {
  topic: 'orders.created',
  numPartitions: 3,
  replicationFactor: 2,
  replicaAssignment: [],
  configEntries: [
    {
      name: 'retention.ms',
      value: '604800000', // Keep messages for 7 days
    },
    {
      name: 'cleanup.policy',
      value: 'delete',
    },
  ],
};

// Pass to the Kafka topic administration or provisioning service.
await kafkaAdmin.createTopic(topicConfig);
```

## AI Coding Instructions

- Provide a unique, descriptive `topic` name that follows the application's Kafka naming conventions.
- Set `numPartitions` based on expected consumer parallelism and throughput; changing partition counts later can affect message ordering assumptions.
- Ensure `replicationFactor` does not exceed the number of available Kafka brokers.
- Use `replicaAssignment` only when explicit partition-to-broker placement is required; otherwise provide an empty array or use the project's standard default.
- Add topic-specific retention, cleanup, and compaction settings through `configEntries` using valid Kafka broker configuration keys.