Cant reach mongo db container - node.js

Question

I trying to implement a dockerized mongo/node based app by this article.
docker-compose.yml
version: '3'
services:
gecar_app:
build:
context: .
dockerfile: Dockerfile.gecars
restart: always
ports:
- 3000:3000
depends_on:
- mongo
command: /usr/app/initAndStartService.sh
mongo:
container_name: mongo
image: mongo
volumes:
- ./data:/data/db
ports:
- "27017:27017"
Dockerfile.gercars
FROM node:latest
RUN mkdir -p /usr/app
WORKDIR /usr/app
COPY src/ /usr/app/src/
COPY package.json /usr/app/package.json
COPY webpack.config.js /usr/app/webpack.config.js
COPY tsconfig.json /usr/app/tsconfig.json
COPY initAndStartService.sh /usr/app/initAndStartService.sh
RUN yarn
RUN yarn build
RUN ["chmod", "+x", "/usr/app/initAndStartService.sh"]
initAndStartService.sh
#!/bin/sh
curl 127.0.0.1:27017
but when run docker-compose up get this:
mongo | 2019-11-19T06:13:21.682+0000 I NETWORK [initandlisten] Listening on 0.0.0.0
mongo | 2019-11-19T06:13:21.683+0000 I NETWORK [initandlisten] waiting for connections on port 27017
...................
gecar_app_1 | Dload Upload Total Spent Left Speed
0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0curl: (7) Failed to connect to 127.0.0.1 port 27017: Connection refused
If I recognize the situation correctly, gecar_app_1 container cant reachmongo` container.

Answer 1

depends_on
Express dependency between services, Service dependencies cause the
following behaviors:
docker-compose up starts services in dependency order. In the following example, db and redis are started before web.
docker-compose up SERVICE automatically includes SERVICE’s dependencies. In the following example, docker-compose up web also
creates and starts db and redis.
docker-compose stop stops services in dependency order. In the following example, web is stopped before db and redis.
in other words, when you want to communicate with the mongo container, all you have to do is to call it as mongo based on your container service naming.
So curl mongo:27017 from the gecar_app container will do the trick

Answer 2

127.0.0.1 is a loopback address, this mean, when you run curl 127.0.0.1:27017 on gecar_app container, you try to connect to itself, but gecar_app did not have any service running on 27017 port. What you need to connect is mongo service (I think so).
You use depends_on to wait until the mongo service started, then start the gecar_app container (good point), now mongo will be come to a hostname, and gecar_app can connect to mongo via mongo "domain".
But, gecar_app maybe started before mongodb service already, then you have make sure that when mongo service already. You can use healthcheck property to do that.
Finally,
docker-compose.yml
version: '3'
services:
gecar_app:
build:
context: .
dockerfile: Dockerfile.gecars
restart: always
ports:
- 3000:3000
depends_on:
- mongo
command: /usr/app/initAndStartService.sh
mongo:
container_name: mongo
image: mongo
volumes:
- ./data:/data/db
ports:
- "27017:27017"
healthcheck:
test: echo 'db.runCommand("ping").ok' | mongo mongo:27017/test --quiet 1
interval: 3s
timeout: 5s
retries: 5
and, initAndStartService.sh
#!/bin/sh
curl mongo:27017