Docker Container Failed to Run - docker

Question

The Dockerfile for my application is as follows
# Tells the Docker which base image to start.
FROM node
# Adds files from the host file system into the Docker container.
ADD . /app
# Sets the current working directory for subsequent instructions
WORKDIR /app
RUN npm install
RUN npm install -g bower
RUN bower install --allow-root
RUN npm install -g nodemon
#expose a port to allow external access
EXPOSE 9000 9030 35729
# Start mean application
CMD ["nodemon", "server.js"]
The docker-compose.yml file is as follows
web:
build: .
links:
- db
ports:
- "9000:9000"
- "9030:9030"
- "35729:35729"
db:
image: mongo:latest
ports:
- "27017:27017"
And the error generated while running is as follows:-
web_1 | [nodemon] 1.11.0
web_1 | [nodemon] to restart at any time, enter `rs`
web_1 | [nodemon] watching: *.*
web_1 | [nodemon] starting `node server.js`
web_1 | Server running at http://127.0.0.1:9000
web_1 | Server running at https://127.0.0.1:9030
web_1 |
web_1 | /app/node_modules/mongodb/lib/server.js:261
web_1 | process.nextTick(function() { throw err; })
web_1 | ^
web_1 | MongoError: failed to connect to server [localhost:27017] on first connect
web_1 | at Pool.<anonymous> (/app/node_modules/mongodb-core/lib/topologies/server.js:313:35)
web_1 | at emitOne (events.js:96:13)
web_1 | at Pool.emit (events.js:188:7)
web_1 | at Connection.<anonymous> (/app/node_modules/mongodb-core/lib/connection/pool.js:271:12)
web_1 | at Connection.g (events.js:291:16)
web_1 | at emitTwo (events.js:106:13)
web_1 | at Connection.emit (events.js:191:7)
web_1 | at Socket.<anonymous> (/app/node_modules/mongodb-core/lib/connection/connection.js:165:49)
web_1 | at Socket.g (events.js:291:16)
web_1 | at emitOne (events.js:96:13)
web_1 | at Socket.emit (events.js:188:7)
web_1 | at emitErrorNT (net.js:1281:8)
web_1 | at _combinedTickCallback (internal/process/next_tick.js:74:11)
web_1 | at process._tickCallback (internal/process/next_tick.js:98:9)
web_1 | [nodemon] app crashed - waiting for file changes before starting...
I have uploaded the image for my application at DockerHub as crissi/airlineInsurance.

Answer 1

In docker you can't connect to an other container via localhost because each container is independend and has its own IP. You should use container_name:port. In your example it should be db:27017 to connect from your NodeJS application in 'web' to the MongoDB in 'db'.
So it's not the problem of your Dockerfile. It's the connection URL from your NodeJS application that points to localhost instead of db.