> ## Documentation Index
> Fetch the complete documentation index at: https://nexus.whatsgood.dog/llms.txt
> Use this file to discover all available pages before exploring further.

# Environment Variables

> Learn how to configure Nexus via environment variables

# Introduction

`Nexus` allows you to configure the server using environment variables. These variables are used in conjunction with the `NexusConfigOptions` interface to configure the Nexus server.

## Environment Variables

Below is a table of standard `Nexus` environment variables that can be set to configure the Nexus server.

| Name                                 | Description                                                                                                                                                                                                                                                                                                                                                                                                                               | Default                                                                                                                 | Required | Example                                                                                                                                                                                                                                       |
| ------------------------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------- | -------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `NEXUS_CHAINS`                       | A JSON array of chains. Each chain should have a `name`, `chainId`, and `blockTime`.                                                                                                                                                                                                                                                                                                                                                      | See [default chains](https://github.com/whats-good/nexus/blob/main/packages/nexus/src/default-chains/default-chains.ts) | No       | `[{"name": "eth_mainnet", "chainId": 1, "blockTime": 12}, [{"name": "base_mainnet", "chainId": 8453, "blockTime": 2}]`                                                                                                                        |
| `NODE_PROVIDERS`                     | A JSON array of node providers. Each provider should have a `name`, `url`, and `chainId`. Each `chainId` should refer to either a [default chains](https://github.com/whats-good/nexus/blob/main/packages/nexus/src/default-chains/default-chains.ts) or a `chainId` set in the `NEXUS_CHAINS` environment variable. Node proviers can additionally have an `weight` field, which defaults to `1`. This value is used for load balancing. | -                                                                                                                       | Yes      | `[{"name": "eth.public", "url":"https://eth.public-rpc.com", "chainId": 1}]` <br /><br />`[{"name": "eth.public", "url":"https://eth.public-rpc.com", "chainId": 1, "weight": 3}, {"name": "tenderly", "url":"", "chainId": 1, "weight": 7}]` |
| `NEXUS_PORT`                         | The port the Nexus server should listen on.                                                                                                                                                                                                                                                                                                                                                                                               | `4000`                                                                                                                  | No       | `4000`                                                                                                                                                                                                                                        |
| `NEXUS_RPC_AUTH_KEY`                 | The secret key used to authenticate requests to the Nexus server.                                                                                                                                                                                                                                                                                                                                                                         | -                                                                                                                       | No       | `my-secret-key`                                                                                                                                                                                                                               |
| `NEXUS_RELAY_ORDER`                  | The order in which to cycle through node providers when a request fails. Can be either `random` or `sequential`.                                                                                                                                                                                                                                                                                                                          | `sequential`                                                                                                            | No       | `random`                                                                                                                                                                                                                                      |
| `NEXUS_RELAY_FAILURE`                | A string or a JSON array that configures error recovery. Can be set to `fail-immediately` or `["cycle-requests", <max number of retries>]`                                                                                                                                                                                                                                                                                                | `["cycle-requests", 3]`                                                                                                 | No       | `["cycle-requests", 5]`                                                                                                                                                                                                                       |
| `NEXUS_LOG_LEVEL`                    | The log level for the Nexus server. Can be set to `debug`, `info`, `warn`, or `error`.                                                                                                                                                                                                                                                                                                                                                    | `info`                                                                                                                  | No       | `debug`                                                                                                                                                                                                                                       |
| `NEXUS_LOG_COLORIZE`                 | Whether to colorize the logs. Can be set to `true` or `false`. Recommended to set to `false` on production.                                                                                                                                                                                                                                                                                                                               | `true`                                                                                                                  | No       | `false`                                                                                                                                                                                                                                       |
| `NEXUS_SUBSCRIPTION_SHARING_ENABLED` | Whether to share ethereum subscription rpc calls accross multiple clients                                                                                                                                                                                                                                                                                                                                                                 | `true`                                                                                                                  | No       | `false`                                                                                                                                                                                                                                       |