Express single site sets up multiple secondary routes corresponding to different nuxt services, but must re-build each startup to request page data?

express has several secondary routes

Primary route

// ./routes/site2
const nuxt=require("./nuxt")
const site2=express.Router()
site2.use("/",nuxt.render)

site1 is deployed so that the entire nuxt project code is in site1/nuxt , and the startup sequence is:
node app.js
each restart will run build
then the .nuxt
site1 generated in the site1/nuxt directory can be displayed

// ./routes/site1/nuxt/index.js
const { Nuxt, Builder } = require("nuxt")
let config = require("./nuxt.config.js")
const nuxt = new Nuxt(config)
const builder = new Builder(nuxt)
builder.build()
module.exports = nuxt

site2 is deployed so that the entire nuxt project code is in site2/nuxt . The startup sequence is

npm run build package nuxt
under

site2 directory site2/nuxt directory .nuxt
node app.js

// ./routes/site2/nuxt/index.js
const { Nuxt, Builder } = require("nuxt")
let config = require("./nuxt.config.js")
config.dev = !(process.env.NODE_ENV === "production")
const nuxt = new Nuxt(config)

module.exports = nuxt

but the site2 page is not displayed until it times out.

1. The route has been tested and can reach

the question now is:
1. npm run build will generate .nuxt . Does nuxt.render only need

to hang on express?

.nuxt
nuxt.config.js

2. What should I do if I don"t want to re-build all the site every time I restart the instance?