I need to run dockers twice so as not to have errors

Question

I am learning how to use Docker in a real-world development environment, so I created a very simple Hello World application in Node.js, with Docker.

package.json

{
  "name": "docker-real-world",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "dependencies": {
    "express": "^4.14.0"
  }
}

server.js (entry point to the application):

var express = require('express');

express()
  .get('/', function(req, res) {
      res.send('Success');
  })
  .listen(3000, function(err) {
      if (!err) { console.log('Server started') }
  });

Dockerfile.dev

FROM mhart/alpine-node:5.6.0

WORKDIR /app
ENV NODE_ENV development
EXPOSE 3000

ADD package.json /app
RUN npm install

Docker-compose.yml

version: "2"
services:
  web:
    build:
        dockerfile: Dockerfile.dev
        context: .
    volumes:
        - .:/app
        - /app/node_modules
    ports:
        - 80:3000
    command: node server.js

: package.json server.js. Dockerfile.dev , . , package.json /app, npm install. , docker-compose.yml. ( , , , /app/node_modules , )

, docker-compose up :

$ docker-compose up

Building web
Step 1 : FROM mhart/alpine-node:5.6.0
 ---> cdbaa8672a25
...
...
web_1  | module.js:341
web_1  |     throw err;
web_1  |     ^
web_1  |
web_1  | Error: Cannot find module 'express'
web_1  |     at Function.Module._resolveFilename (module.js:339:15)
web_1  |     at Function.Module._load (module.js:290:25)
web_1  |     at Module.require (module.js:367:17)
web_1  |     at require (internal/module.js:16:19)
web_1  |     at Object.<anonymous> (/app/server.js:1:77)
web_1  |     at Module._compile (module.js:413:34)
web_1  |     at Object.Module._extensions..js (module.js:422:10)
web_1  |     at Module.load (module.js:357:32)
web_1  |     at Function.Module._load (module.js:314:12)
web_1  |     at Function.Module.runMain (module.js:447:10)
dockerrealworld_web_1 exited with code 1

( - ), :

$ docker-compose up

Starting dockerrealworld_web_1
Attaching to dockerrealworld_web_1
web_1  | Server started

? ?

Answer 1

. Docker ...

# Create the location of our app within the image
RUN mkdir -p /usr/src/app
WORKDIR /usr/src/app

# Copy the package json containing dependencies, then install
COPY package.json /usr/src/app/
RUN npm install

# Copy the current source to the image
COPY . /usr/src/app

# Start the service
ENTRYPOINT ["npm", "start"]

, .