如何构建 docker 容器端口？ 使用--net 还是--link？

Question

I have 2 docker containers. One contains a simple node.js web app which contains server information and MongoDB connection details. The second contains a running instance of MongoDB.

I am attempting to run the web app container to connect to the MongoDB container like so:

docker run --link mongodb2:mongodb2 -p 49160:8080 -it --name web node-web-app

Doing this I can successfully access and view the hosted page at http://hostname:49160/ but I cannot connect to MongoDB.

Another method I have tried is:

docker run --net container:mongodb2 -ti --name web node-web-app

Here I can successfully connect to MongoDB, but I cannot access my hosted page at http://hostname:27017/. Instead I receive the message:

It looks like you are trying to access MongoDB over HTTP on the native driver port.

I have also attempted to pass port details like so using the --net method:

docker run --net container:mongodb2 -p 49160:8080 -ti --name web node-web-app

but I receive a docker error:

docker: Error response from daemon: conflicting options: port publishing and the container type network mode.
See 'docker run --help'.

I believe there is an issue with the way I am configuring my ports, but I am new to both docker and setting up web servers.

Here is my web app code:

'use strict';
const express = require('express');
// App
const app = express();

// Constants
const PORT = 8080;
const HOST = '0.0.0.0';

const MongoClient = require('mongodb').MongoClient;

// Connect URL
const url = 'mongodb://127.0.0.1:27017';

var db;
var ticket;

MongoClient.connect(url, {
    useNewUrlParser: true,
    useUnifiedTopology: true
}, (err, client) => {
    if (err) {
        return console.log(err);
    }

    // Specify database you want to access

    db = client.db('DB');

    console.log(`MongoDB Connected: ${url}`);

    ticket = db.collection('ticket');

    ticket.find().toArray((err, results) => {
        console.log(results);
    });

});

//Routes
app.get('/', (req, res) => {
  res.sendFile(__dirname + '/index.html')
});


app.listen(PORT, HOST);
console.log(`Running on http://${HOST}:${PORT}`)

Answer 1

You should use a named Docker network to connect between containers. Once you do, the other containers' names will be usable as host names.

docker network create some-network
docker run -d --net some-network --name mongodb2 mongo
docker run -d --net some-network --name app -p 49160:8080 node-web-app

In your source code, you can't hard-code the location of the database, since it's somewhat likely it won't be on the same machine or in the same container when you deploy it. localhost could be a reasonable developer default but the option needs to be configurable.

const mongoHost = process.env.MONGO_HOST || 'localhost';
const url = `mongodb://${mongoHost}:27017`;

docker run ... -e MONGO_HOST=mongodb2 ...

If you're using Docker Compose to launch things, it provides a default network for you (different from the "default bridge network" in the core Docker documentation) and you need to do very little setup; just use the other container's Compose service name as a host name.

version: '3.8'
services:
  mongodb2:
    image: mongo
  app:
    build: .
    ports: ['49160:8080']
    environment:
      - MONGO_HOST=mongodb2

Of the other options you propose, --link is considered obsolete now that named networks have essentially replaced it. Setting one container to run in another's network namespace is also a very unusual setup, and it comes with limitations like what you show.