How to access Docker container app on local? - node.js

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

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

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

You need to publish ports
docker run -p 3000:3000 <my image>
-p - stands for publish