How to access Docker container app on local?

Question

I have a simple Node.js/Express app:

const port = 3000

app.get('/', (req, res) => res.send('Hello World!'))

app.listen(port, () => console.log(`Example app listening on port ${port}!`))

It works fine when I start it like: node src/app.js

Now I'm trying to run it in a Docker container. Dockerfile is:

FROM node:8

WORKDIR /app
ADD src/. /app/src
ADD package.json package-lock.json /app/

RUN npm install

COPY . /app

EXPOSE 3000

CMD [ "node", "src/app.js" ]

It starts fine: docker run <my image>:

Listening on port 3000

But now I cannot access it in my browser: http://localhost:3000

This site can’t be reached localhost refused to connect.

Same happen if I try to run it within docker-compose:

version: '3.4'

services:
  service1:
    image: xxxxxx
    ports:
      - 8080:8080
    volumes:
      - xxxxxxxx
  myapp:
    build: 
      context: .
      dockerfile: Dockerfile
    networks:
      - private
    ports:
      - 3000
    command:
      node src/app.js

Not sure if I deal right with ports in both docker files

Answer 1

You need to publish ports

docker run -p 3000:3000 <my image>

-p - stands for publish

Answer 2

try this:

services:
  myapp:
    build: 
      context: .
      dockerfile: Dockerfile
    networks:
      - private
    ports:
      - 3000:3000 ##THIS IS THE CHANGE, YOU NEED TO MAP MACHINE PORT TO CONTAINER
    command:
      node src/app.js

Answer 3

When you work with docker you must define the host for your app as 0.0.0.0 instead of localhost .

For your express application you can define the host on app.listen call.

Check the documentation : app.listen([port[, host[, backlog]]][, callback])

Your express code should be updated to:

const port = 3000
const host = '0.0.0.0'

app.get('/', (req, res) => res.send('Hello World!'))

app.listen(port, host, () => console.log(`Example app listening on ${port}!`))

It's also important publish docker ports:

• Running docker: docker run -p 3000:3000 <my image>
• Running docker-compose:

services:
  myapp:
    build: 
      context: .
      dockerfile: Dockerfile
    networks:
      - private
    ports:
      - 3000:3000
    command:
      node src/app.js