# Environment Variables

All environment variables are **required** at startup. If any is missing, the binary exits immediately — no silent defaults, no fallback configuration.

## Runtime Variables

These variables must be set when starting the ledger binary.

### Server

| Variable      | Description              | Example |
| ------------- | ------------------------ | ------- |
| `LEDGER_PORT` | HTTP port for the server | `8080`  |

### License

| Variable              | Description                                          | Example                   |
| --------------------- | ---------------------------------------------------- | ------------------------- |
| `LEDGER_LICENSE_PATH` | Path to the `license.jwt` file — verified at startup | `/etc/ledger/license.jwt` |

### Database

| Variable                | Description                                          | Example                                        |
| ----------------------- | ---------------------------------------------------- | ---------------------------------------------- |
| `LEDGER_DB_MASTER_URL`  | PostgreSQL connection string for the master (writes) | `postgres://user:pass@master.rds:5432/ledger`  |
| `LEDGER_DB_REPLICA_URL` | PostgreSQL connection string for the replica (reads) | `postgres://user:pass@replica.rds:5432/ledger` |
| `LEDGER_DB_POOL_SIZE`   | Maximum connections per pool (master and replica)    | `10`                                           |
| `LEDGER_DB_TLS`         | Enable TLS for database connections                  | `true` (must be `true` in production)          |

{% hint style="danger" %}
`LEDGER_DB_TLS` must be set to `true` in production. TLS certificates are included in the container image's system trust store by default (Amazon Linux).
{% endhint %}

### Batch Engine

| Variable                  | Description                                    | Example |
| ------------------------- | ---------------------------------------------- | ------- |
| `LEDGER_BATCH_SIZE`       | Maximum transactions per batch before flushing | `150`   |
| `LEDGER_BATCH_TIMEOUT_MS` | Maximum wait time (ms) before flushing a batch | `15`    |

The batch engine flushes when either condition is met — whichever comes first.

### Idempotency

| Variable                                  | Description                                   | Example |
| ----------------------------------------- | --------------------------------------------- | ------- |
| `LEDGER_IDEMPOTENCY_TTL_HOURS`            | How long idempotency records are kept (hours) | `1`     |
| `LEDGER_IDEMPOTENCY_CLEANUP_INTERVAL_MIN` | How often the cleanup job runs (minutes)      | `5`     |

**Recommended values:** TTL of 1 hour with cleanup every 5 minutes. The first cleanup run is delayed by the configured interval after startup.

### Console

| Variable             | Description                                          | Example                           |
| -------------------- | ---------------------------------------------------- | --------------------------------- |
| `LEDGER_CONSOLE_URL` | Base URL for the vendor Console (heartbeat endpoint) | `https://console.entrytarget.com` |

### Logging

| Variable   | Description          | Example         |
| ---------- | -------------------- | --------------- |
| `RUST_LOG` | Log level (optional) | `info`, `debug` |

This is the only optional variable. If not set, default logging is used.

## Production Configuration Example

```bash
LEDGER_LICENSE_PATH="/etc/ledger/license.jwt"
LEDGER_PORT=8080
LEDGER_DB_MASTER_URL="postgres://ledger:password@master.cluster.us-east-1.rds.amazonaws.com:5432/ledger"
LEDGER_DB_REPLICA_URL="postgres://ledger:password@replica.cluster.us-east-1.rds.amazonaws.com:5432/ledger"
LEDGER_DB_POOL_SIZE=20
LEDGER_DB_TLS=true
LEDGER_BATCH_SIZE=200
LEDGER_BATCH_TIMEOUT_MS=15
LEDGER_IDEMPOTENCY_TTL_HOURS=1
LEDGER_IDEMPOTENCY_CLEANUP_INTERVAL_MIN=5
LEDGER_CONSOLE_URL="https://console.entrytarget.com"
```

## Tuning Recommendations

See the [Tuning Guide](/docs/performance/tuning.md) for detailed recommendations on batch size, timeout, and pool size settings based on your workload.

| Workload      | `BATCH_SIZE` | `BATCH_TIMEOUT_MS` | `DB_POOL_SIZE` |
| ------------- | ------------ | ------------------ | -------------- |
| Low volume    | 150          | 20                 | 10             |
| Medium volume | 200          | 15                 | 20             |
| High volume   | 300          | 10                 | 40             |


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