通过CloudFlare Worker搭建负载均衡服务器

let nodes = [
  "https://api.justyy.com",
  "https://api.steemyy.com"
];

function reverse(promise) {
    return new Promise((resolve, reject) => Promise.resolve(promise).then(reject, resolve));
}
 
function promiseAny(iterable) {
    return reverse(Promise.all([...iterable].map(reverse)));
};

async function contactServer(server) {
  return new Promise((resolve, reject) => {
    fetch(server, {
      method: "GET"
    }).then(response => {
      resolve({
        "server": server,
      });
    }).catch(function(error) {
      reject(error);
    });
  });
}

function handleOptions(request) {
  // Make sure the necesssary headers are present
  // for this to be a valid pre-flight request
  if (
    request.headers.get('Origin') !== null &&
    request.headers.get('Access-Control-Request-Method') !== null &&
    request.headers.get('Access-Control-Request-Headers') !== null
  ) {
    // Handle CORS pre-flight request.
    // If you want to check the requested method + headers
    // you can do that here.
    return new Response(null, {
      headers: corsHeaders,
    })
  } else {
    // Handle standard OPTIONS request.
    // If you want to allow other HTTP Methods, you can do that here.
    return new Response(null, {
      headers: {
        Allow: 'GET, HEAD, POST, OPTIONS',
      },
    })
  }
}
 
addEventListener('fetch', event => {
  const request = event.request;
  const method = request.method.toUpperCase();
  if (method === 'OPTIONS') {
    // Handle CORS preflight requests
    event.respondWith(handleOptions(request))
  } else if (
    method === 'GET' ||
    method === 'HEAD' ||
    method === 'POST'
  ) {
    // Handle requests to the API server
    event.respondWith(handleRequest(request))
  } else {
    event.respondWith(
      new Response(null, {
        status: 405,
        statusText: 'Method Not Allowed',
      }),
    )
  }
});

async function forwardRequestGET(apiURL) {
  return new Promise((resolve, reject) => {
    fetch(apiURL, {
      method: "GET",   
      headers: {
        'Content-Type': 'application/json'
      },
      redirect: "follow"
    }).then(response => {
      resolve(response.text());
    }).catch(function(error) {
      reject(error);
    });
  });
}
 
async function forwardRequestPOST(apiURL, body) {
  return new Promise((resolve, reject) => {
    fetch(apiURL, {
      method: "POST",   
      redirect: "follow",
      headers: {
      'Content-Type': 'application/json'
      },      
      body: body
    }).then(response => {
      resolve(response.text());
    }).catch(function(error) {
      reject(error);
    });
  });
}

/**
 * Respond to the request
 * @param {Request} request
 */
async function handleRequest(request) {
  const country = request.headers.get('cf-ipcountry');
  const servers = [];
  for (const server of nodes) {
    servers.push(contactServer(server));
  }
  const load = await promiseAny(servers);    
  const forwardedURL = load['server'];
  const method = request.method.toUpperCase();
  let result;
  let res;
  let version = "";
  try {
    version = await getVersion(load['server']);
  } catch (e) {
    version = JSON.stringify(e);
  }
  try {    
    if (method === "POST") {
      const body = await request.text();    
      result = await forwardRequestPOST(forwardedURL, body);
    } else if (method === "GET") {
      result = await forwardRequestGET(forwardedURL);
    } else {
      res = new Response(null, {
        status: 405,
        statusText: 'Method Not Allowed',
      });
      res.headers.set('Access-Control-Allow-Origin', '*');
      res.headers.set('Cache-Control', 'max-age=3600');    
      res.headers.set("Origin", load['server']);
      res.headers.set("Country", country);
      return res;
    }
    res = new Response(result, {status: 200});    
    res.headers.set('Content-Type', 'application/json');
    res.headers.set('Access-Control-Allow-Origin', '*');
    res.headers.set('Cache-Control', 'max-age=3');
    res.headers.set("Origin", load['server']);
    res.headers.set("Version", version);
    res.headers.set("Country", country);
  } catch (e) {
    res = new Response(JSON.stringify(result), {status: 500});
    res.headers.set('Content-Type', 'application/json');
    res.headers.set('Access-Control-Allow-Origin', '*');
    res.headers.set('Cache-Control', 'max-age=3');    
    res.headers.set("Origin", load['server']);
    res.headers.set("Version", version);
    res.headers.set("Country", country);
    res.headers.set("Error", JSON.stringify(e));
  }
  return res;
}

async function getVersion(server) {
  return new Promise((resolve, reject) => {
    fetch(server, {
      method: "POST",
      headers: {
        'Content-Type': 'application/json'
      },
      body: JSON.stringify({"id":0,"jsonrpc":"2.0","method":"call","params":["login_api","get_version",[]]})
    }).then(response => {
      resolve(response.text());
    }).catch(function(error) {
      reject(error);
    });
  });
}