To interact with Arbitrum One and the RinkArby testnet, you can rely on the same popular node providers that you are already using on Ethereum. There are multiple providers that may help you build on Arbitrum, here is a list of a couple of them.
Alchemy provides endpoints for both Arbitrum One (Mainnet) and Rinkeby testnet. To use these RPC endpoints, you need an Alchemy API key to authenticate your requests. For detailed steps of how to create one, see the Alchemy's documentation. Next, depending one which network you want to interact with, you can choose between the two RPC endpoints provided by Alchemy and interact with them directly in the command line or point your MetaMask RPC endpoints to them. For more information on Arbitrum JSON-RPC API methods supported by Alchemy, check out the official documentation.
Infura is a node service provider that provides access to Arbitrum One (Mainnet) and RinkArby testnet. To start interacting with either of these networks, you need to set up an Infura account and create a project. Next, you will be given a Project ID (for detailed steps, check out the Infura's documentation). You can now select which endpoint you want to connect to, this could be Arbitrum One, or it could be Rinkeby testnet.
QuickNode supports both Arbitrum One (Mainnet) and Rinkeby testnet and allows users to interact with these chains. For a full guide of how to set up an Arbitrum node on QuickNode, see the QuickNode's Arbitrum RPC documentation.
Moralis allows Arbitrum users and developers to connect to both Arbitrum One (Mainnet) and Rinkeby testnet. To do so, you need to create an account and choose the node you wish to connect to. You will then be presented with a pair of URLs (Arbitrum Mainnet and Testnet) with which you can interact with directly in the command line or point your MetaMask RPC endpoints to them. For full guide and more explanation, see the Moralis's documentation.
Ankr provides access to both Arbitrum One (Mainnet) and Rinkeby Testnet. After creating an Ankr account, you will be presented with a pair of URLs which you can use to connect to any of our networks. For more details, see the Ankr's documentation.
BlockVision provides Arbitrum One mainnet and Rinkeby node services. See BlockVision Dashboard.