can you give a broad overview of what this code is doing :  "require('dotenv').config();
const newRelic = require('newrelic');
const port = process.env.PORT;
const host = process.env.HOST;
const environment = process.env.NODE_ENV;
//logger
// Require the framework and instantiate it
const app = require('fastify')({
    genReqId: function (req) { return Math.random().toString(26).slice(2) },
    logger: {
        level: process.env.LOG_LEVEL || 'info',
        base: { pid: undefined, hostname: undefined },
        serializers: {
            req(req) {
                return {
                    method: req.method,
                    url: req.url,                    
                    "user-agent": req.headers['user-agent']
                }
            }
        }
    }
})
const { newSolrcoredb, existingSolrcoredb, existingSolrcoreClientdb } = require('./config/v1/databasev1');
const response = require('./helpers/v1/Responsehelper'); //Response helpers
const responseCode = require('./helpers/v1/Responsecode'); //Resonse code
// app.register(require('fastify-cors'), {});   // Commented to avoid sending vary header
const { removeSpecialcharactersAndgarbageValues, SuccessAndErrorMessage } = require('./utils/v1/RequestPayloadUtilities');
const Redis = require("ioredis");
const redisCredential = require('./config/v1/rediscredentialsv1').getCredentials(environment);
const redisDatabase = new Redis.Cluster([{
    "port": redisCredential.port,
    "host": redisCredential.host
}], {
    clusterRetryStrategy: function (times) {
        var delay = Math.min(100 + times * 2, 2000);
        return delay;
    }
});

redisDatabase.on('error', function (err) {
    redisdb.connected = false;
    app.log.info({ "REDIS_STATUS": "ERROR", "MESSAGE": `REDIS DATABASE CONNECTION ERROR:${err}` });
});

redisDatabase.on('connect', function () {
    redisdb.connected = true;
    app.log.info({ "REDIS_STATUS": "SUCCESS", "MESSAGE": "REDIS DATABASE CONNECTED SUCCESSFULLY.! " });
    // const minutelydata = require('./public/minutely.json');
    // redisDatabase.hmset("minutely-data", minutelydata);
    // redisDatabase.end(true);
});

//Global declarations
global.solrdbzeev1 = newSolrcoredb(); //SOLR NEW;
global.solrdbzeev2 = existingSolrcoredb(); //SOLR EXISTING;
global.solrclientdbzeev2 = existingSolrcoreClientdb(); //SOLR EXISTING;
global.applog = app;
global.response = response;
global.responseCode = responseCode;
global.redisdb = redisDatabase;

// Declare a route -[version-v1]
const collectionsRoute = require('./routes/v1/AllCollections');
app.get('/', (req, res) => res.status(responseCode.HTTP_OK).send({ message: SuccessAndErrorMessage().SERVER_HEALTHY })); //Healthy entry
app.register(collectionsRoute);

//Empty response handler
app.addHook('onSend', async (request, response, payload) => {
    if (response.statusCode === responseCode.HTTP_OK && (payload === '' || payload === '{}')) {
        response.code(responseCode.HTTP_INTERNAL_SERVER_ERROR);
        return payload;
    }
    return payload;
});

//request Payload Pre Validation
app.addHook('preValidation', (request, reply, done) => {
    if (request.url == SuccessAndErrorMessage().URL_BASE_PATH_SLASH) {
        done()
    } else {
        const collectionId = removeSpecialcharactersAndgarbageValues(request.params.collectionid);
        if (collectionId) {
            request.params.collectionid = collectionId;
            done()
        } else {
            reply.status(responseCode.HTTP_UNPROCESSABLE_ENTITY).send({ message: SuccessAndErrorMessage().COLLECTION_ID_INVALID });
        }
    }
});

// Run the server!
const start = async () => {
    try {
        await app.listen(port, host);
        console.log(`App listening on port is : ${port}!`);
    } catch (err) {
        app.log.error(err)
        process.exit(1);
    }
};

start()

module.exports = app;"