# FAQ

> Source: https://docs.erpc.cloud/faq
> Frequently asked questions about running, configuring, and troubleshooting eRPC.
> Format: machine-readable markdown export of the docs page above.
> All collapsible AI sections are inlined and fully expanded.

## Frequently Asked Questions

### How to set env variables?

To use env variables in [erpc.yaml](/config/example.llms.txt), follow these steps:

1. **Set env variables**: Define the env variables in your system or shell before running your application:

```bash
export ETHEREUM_RPC_URL=https://mainnet.infura.io/v3/YOUR_INFURA_KEY
````

2. **Use placeholders in config**: Add placeholders in your config file where you want the env variables to be used:

**Config path:** `projects > upstreams[]`

**YAML — `erpc.yaml`:**

```yaml
projects:
  - id: main
    upstreams:
      - endpoint: \${ETHEREUM_RPC_URL}
```

**TypeScript — `erpc.ts`:**

```typescript
projects: [{
  id: "main",
  upstreams: [
    { endpoint: process.env.ETHEREUM_RPC_URL },
  ],
}]
```

### How to disable caching?

To disable caching, set [`evmJsonRpcCache`](/config/database/evm-json-rpc-cache.llms.txt) to `null` in your configuration:

**Config path:** `database > evmJsonRpcCache`

**YAML — `erpc.yaml`:**

```yaml
database:
  evmJsonRpcCache: ~
```

**TypeScript — `erpc.ts`:**

```typescript
database: {
  evmJsonRpcCache: null,
}
```

### How do I set up CORS for frontend usage?

If you’re deploying eRPC on Railway (or elsewhere) and plan to call it directly from a web application in the browser, you must enable CORS in your [erpc.yaml](/config/projects/cors.llms.txt#config). Below is a minimal example that allows requests from a specific origin or any origin:

```yaml filename="erpc.yaml"
projects:
  - id: main
    cors:
      allowedOrigins: 
        # If you want to allow all origins, use "*" which means any frontend can make calls to your erpc instance
        - "https://myapp.com"
      allowedMethods: 
        - "GET"
        - "POST"
        - "OPTIONS"
      allowedHeaders:
        - "Content-Type"
      allowCredentials: false
      maxAge: 300
```