Register a WAMP procedure on more than one service. The idea being that a backup version of the service will register automatically if the primary one goes down.

app.js

import autobahn from 'autobahn';

const RPC_ADD2 = 'com.myapp.add2';

let connection = new autobahn.Connection({
  url: 'ws://127.0.0.1:9000/ws',
  realm: 'realm1',
  use_es6_promises: true
});

connection.onopen = onOpen;
connection.open();

function add2(args) {
  return args[0] + args[1];
}

async function attach(session) {
  await session.register(RPC_ADD2, add2);
  session.log('Registered');
}

async function onOpen(session) {
  try {
    let id = await session.call('wamp.registration.lookup', [RPC_ADD2]);
    let reg;
    if (id) {
       reg = await session.call('wamp.registration.get', [id]);
    }
    if (reg && reg.uri === RPC_ADD2) {
      session.log('Waiting...');
      session.subscribe('wamp.registration.on_unregister', () => attach(session));
    } else {
      await attach(session);
    }
  } catch (error) {
    session.log(error);
  }
}