# ServerFactory

**Kind:** Class

**Source:** [`packages/microservices/server/server-factory.ts`](https://github.com/nestjs/nest/blob/master/packages/microservices/server/server-factory.ts#L20)

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

`ServerFactory` creates the appropriate NestJS microservice server implementation for a configured transport, such as TCP, Redis, NATS, MQTT, gRPC, or Kafka. It centralizes transport-to-server resolution so the rest of the microservices package can work with a common server interface.

## Methods

| Method | Signature | Returns |
|---|---|---|
| `create` | `create(microserviceOptions: MicroserviceOptions)` | `void` |

## Diagram

```mermaid
graph LR
  A[MicroserviceOptions] --> B[ServerFactory.create()]
  B --> C{transport}
  C -->|TCP| D[ServerTCP]
  C -->|Redis| E[ServerRedis]
  C -->|NATS| F[ServerNats]
  C -->|MQTT| G[ServerMqtt]
  C -->|gRPC| H[ServerGrpc]
  C -->|Kafka / RMQ| I[Transport-specific Server]
  D --> J[Microservice Server Interface]
  E --> J
  F --> J
  G --> J
  H --> J
  I --> J
```

## Usage

```ts
import { Transport } from '@nestjs/microservices';
import { ServerFactory } from '@nestjs/microservices/server/server-factory';

const server = ServerFactory.create({
  transport: Transport.TCP,
  options: {
    host: '127.0.0.1',
    port: 3001,
  },
});

server.listen(() => {
  console.log('TCP microservice server is listening');
});
```

## AI Coding Instructions

- Pass a valid `MicroserviceOptions` object with the intended `Transport` value and transport-specific options.
- Treat the returned value as a common microservice server abstraction; avoid coupling calling code to a specific `Server*` implementation.
- Add support for new transports by extending the factory mapping and returning a server implementation compatible with the existing server contract.
- Ensure transport options match the selected transport; TCP options, broker credentials, and gRPC package settings are not interchangeable.
- Prefer using Nest application factory APIs in application code when possible; use `ServerFactory` directly for framework-level or custom integration scenarios.

## How it works

`ServerFactory` is a class with one static method, `create`, that constructs a transport-specific microservice server from a `MicroserviceOptions` configuration. It reads `transport` and `options` from the input after a TypeScript-only exclusion of the `CustomStrategy` union member. [packages/microservices/server/server-factory.ts:20-25](packages/microservices/server/server-factory.ts#L20-L25)

`create` selects the constructed class as follows:

- `Transport.REDIS` → `ServerRedis` [packages/microservices/server/server-factory.ts:26-28](packages/microservices/server/server-factory.ts#L26-L28)
- `Transport.NATS` → `ServerNats` [packages/microservices/server/server-factory.ts:29-30](packages/microservices/server/server-factory.ts#L29-L30)
- `Transport.MQTT` → `ServerMqtt` [packages/microservices/server/server-factory.ts:31-32](packages/microservices/server/server-factory.ts#L31-L32)
- `Transport.GRPC` → `ServerGrpc` [packages/microservices/server/server-factory.ts:33-34](packages/microservices/server/server-factory.ts#L33-L34)
- `Transport.KAFKA` → `ServerKafka` [packages/microservices/server/server-factory.ts:35-36](packages/microservices/server/server-factory.ts#L35-L36)
- `Transport.RMQ` → `ServerRMQ` [packages/microservices/server/server-factory.ts:37-38](packages/microservices/server/server-factory.ts#L37-L38)
- Any other value, including an omitted `transport`, → `ServerTCP` [packages/microservices/server/server-factory.ts:39-40](packages/microservices/server/server-factory.ts#L39-L40). The repository test asserts that `create({})` returns a `ServerTCP`. [packages/microservices/test/server/server-factory.spec.ts:13-16](packages/microservices/test/server/server-factory.spec.ts#L13-L16)

The method passes `options` directly to `ServerGrpc`; for the other constructors, it applies a type assertion to the corresponding transport’s `options` type. These assertions do not perform runtime validation. [packages/microservices/server/server-factory.ts:21-40](packages/microservices/server/server-factory.ts#L21-L40) The factory itself has no input checks, fallback error, or `try`/`catch`; errors thrown while constructing a selected server escape from `create`. [packages/microservices/server/server-factory.ts:21-42](packages/microservices/server/server-factory.ts#L21-L42)

Construction can have immediate side effects before a server starts listening. For example, `ServerTCP` initializes its underlying server and serializer/deserializer in its constructor, [packages/microservices/server/server-tcp.ts:49-60](packages/microservices/server/server-tcp.ts#L49-L60) while the Redis, NATS, MQTT, Kafka, RMQ, and gRPC constructors load their respective external packages. [packages/microservices/server/server-redis.ts:42-50](packages/microservices/server/server-redis.ts#L42-L50) [packages/microservices/server/server-nats.ts:50-58](packages/microservices/server/server-nats.ts#L50-L58) [packages/microservices/server/server-mqtt.ts:47-56](packages/microservices/server/server-mqtt.ts#L47-L56) [packages/microservices/server/server-kafka.ts:78-85](packages/microservices/server/server-kafka.ts#L78-L85) [packages/microservices/server/server-rmq.ts:77-95](packages/microservices/server/server-rmq.ts#L77-L95) [packages/microservices/server/server-grpc.ts:70-88](packages/microservices/server/server-grpc.ts#L70-L88)

`MicroserviceOptions` also permits `CustomStrategy`, whose shape has `strategy` and optional `options` rather than `transport`. [packages/microservices/interfaces/microservice-configuration.interface.ts:25-33](packages/microservices/interfaces/microservice-configuration.interface.ts#L25-L33) [packages/microservices/interfaces/microservice-configuration.interface.ts:50-53](packages/microservices/interfaces/microservice-configuration.interface.ts#L50-L53) In the visible `NestMicroservice` caller, configurations with `strategy` bypass `ServerFactory.create` and assign that strategy as the server instance. [packages/microservices/nest-microservice.ts:84-109](packages/microservices/nest-microservice.ts#L84-L109)