Apollo GraphQL subscriptions is not working in Vuejs

问题

I am using GraphQL Subscription with Prisma and vuejs + apollo client

In local system, I am running vuejs at http://localhost:8080 and server at http://localhost:4000.

I want to display recently added and updated records in dashboard.

I have implemented subscription in my local system and it's working proper.

I push all server side and client side code to server but subscription is not working there.

I am using AWS server. Everything is working proper except subscription. I set up websockets and it's also working proper.

Sometime I am getting below error: WebSocket connection to 'wss://URL:4000/graphql' failed: WebSocket is closed before the connection is established

I am following below docuemnt https://www.apollographql.com/docs/react/data/subscriptions/

I have a tried a different ways but didn't get success. The connection is stable/ reconnects after disconnecting itself.

At server side, I added listener for web socket and it's connecting.

This is my code of vue-apollo.js file

    import Vue from 'vue';
    import VueApollo from 'vue-apollo';
    import { ApolloClient } from 'apollo-client';
    import { HttpLink } from 'apollo-link-http';
    import { InMemoryCache } from 'apollo-cache-inmemory';

    // imports for subscription
    import { split } from 'apollo-link';
    import { WebSocketLink } from 'apollo-link-ws';
    import { getMainDefinition } from 'apollo-utilities';

    const uriHttp = process.env.VUE_APP_SERVER_URL;
    const uriWs = process.env.VUE_APP_WS_SERVER_URL;

    const headers = { authorization: localStorage.getItem('token') };

    const httpLink = new HttpLink({ uri: uriHttp, headers });
    const wsLink = new WebSocketLink({
      uri: uriWs,
      options: {
        reconnect: true,
        connectionParams() {
           return { headers };
         },
      },
    });

    wsLink.subscriptionClient.on('connecting', () => {
      console.log('connecting');
    });

    wsLink.subscriptionClient.on('connected', () => {
      console.log('connected');
    });

    wsLink.subscriptionClient.on('reconnecting', () => {
      console.log('reconnecting');
    });

    wsLink.subscriptionClient.on('reconnected', () => {
      console.log('reconnected');
    });

    wsLink.subscriptionClient.on('disconnected', () => {
      console.log('disconnected');
    });

    wsLink.subscriptionClient.maxConnectTimeGenerator.duration = () => wsLink.subscriptionClient.maxConnectTimeGenerator.max;

   const link = split(({ query }) => {
      const { kind, operation } = getMainDefinition(query);
      return kind === 'OperationDefinition' && operation === 'subscription';
    }, wsLink, httpLink);

    export const defaultClient = new ApolloClient({
      link,
      cache: new InMemoryCache(),
      connectToDevTools: true,
    });

    const apolloProvider = new VueApollo({
      defaultClient,
      defaultOptions: {
        $loadingKey: 'loading',
      },
    });

    Vue.use(VueApollo);

    export default apolloProvider;