# Appsettings

This page explains how Ksql.Linq reads configuration and which keys are commonly used.

## Sources and precedence (override order)
Ksql.Linq uses the standard .NET configuration stack. Later sources override earlier ones:
- Code (builder / Fluent APIs)
- Environment variables (`DOTNET_...` / `KsqlDsl__...` etc.)
- `appsettings.{Environment}.json`
- `appsettings.json`
- Library defaults

Note: The typical .NET pattern is AddJsonFile → AddEnvironmentVariables → AddCommandLine; the last wins. `KsqlContextBuilder` respects the resolved `IConfiguration` you pass in.

## Minimal configuration
```json
{
  "KsqlDsl": {
    "Common": { "BootstrapServers": "localhost:9092", "ClientId": "my-app" },
    "SchemaRegistry": { "Url": "http://localhost:8081" },
    "KsqlDbUrl": "http://localhost:8088",
    "DlqTopicName": "dead-letter-queue",
    "DeserializationErrorPolicy": "DLQ"
  }
}
```

## Key sections
- `KsqlDsl.Common.*`: base Kafka Producer/Consumer options (e.g., `BootstrapServers`)
- `KsqlDsl.SchemaRegistry.Url`: Schema Registry URL
- `KsqlDsl.KsqlDbUrl`: ksqlDB REST URL
- `KsqlDsl.DlqTopicName`, `KsqlDsl.DeserializationErrorPolicy`: DLQ settings
- `KsqlDsl.Topics.<name>.Creation.*`: topic creation (partitions/replication/retention, etc.)
- `KsqlDsl.Topics.<name>.Consumer|Producer.*`: per-topic consumer/producer options

## Secured Kafka (SASL_SSL) example
```json
{
  "KsqlDsl": {
    "Common": {
      "BootstrapServers": "<broker1>:9092,<broker2>:9092",
      "SecurityProtocol": "SaslSsl",
      "SaslMechanism": "Plain",
      "SaslUsername": "${CLOUD_API_KEY}",
      "SaslPassword": "${CLOUD_API_SECRET}"
    },
    "SchemaRegistry": { "Url": "https://<sr-host>:8081" },
    "KsqlDbUrl": "https://<ksqldb-host>:8088"
  }
}
```

## Table/TimeBucket state store (RocksDB)
For how local state is used and maintained, see: [Tumbling-State-Store](Tumbling-State-Store)

## See also
- Kafka connection options: [Appsettings-Kafka](Appsettings-Kafka)
- Full configuration reference: [Configuration-Reference](Configuration-Reference)