How do I seed a mongo database using docker-compose?

I do this using another docker container whose only purpose is to seed mongo, then exit. I suspect this is the same idea as ebaxt's, but when I was looking for an answer to this, I just wanted to see a quick-and-dirty, yet straightforward, example. So here is mine:

docker-compose.yml

mongodb:  image: mongo  ports:    - "27017:27017"mongo-seed:  build: ./mongo-seed  links:    - mongodb# my webserver which uses mongo (not shown in example)webserver:  build: ./webserver  ports:    - "80:80"  links:    - mongodb

mongo-seed/Dockerfile

FROM mongoCOPY init.json /init.jsonCMD mongoimport --host mongodb --db reach-engine --collection MyDummyCollection --type json --file /init.json --jsonArray

mongo-seed/init.json

[  {    "name": "Joe Smith",    "email": "jsmith@gmail.com",    "age": 40,    "admin": false  },  {    "name": "Jen Ford",    "email": "jford@gmail.com",    "age": 45,    "admin": true  }]

I have found useful to use Docker Custom Images and using volumes, instead of creating another container for seeding.

File Structure

.├── docker-compose.yml├── mongo│   ├── data│   ├── Dockerfile│   └── init-db.d│       └── seed.js

Every File location mentioned in Dockerfile/docker-compose.yml, is relative to location of docker-compose.yml

DOCKERFILE

FROM mongo:3.6COPY ./init-db.d/seed.js /docker-entrypoint-initdb.d

docker-compose.yml

version: '3'services:  db:    build: ./mongo    restart: always    volumes:      - ./mongo/data:/data/db #Helps to store MongoDB data in `./mongo/data`    environment:      MONGO_INITDB_ROOT_USERNAME: {{USERNAME}}      MONGO_INITDB_ROOT_PASSWORD: {{PWD}}      MONGO_INITDB_DATABASE: {{DBNAME}}

seed.js

// Since Seeding in Mongo is done in alphabetical order... It's is important to keep// file names alphabetically ordered, if multiple files are to be run.db.test.drop();db.test.insertMany([  {    _id: 1,    name: 'Tensor',    age: 6  },  {    _id: 2,    name: 'Flow',    age: 10  }])

docker-entrypoint-initdb.d can be used for creating different users and mongodb administration related stuffs, just create an alphabetical ordered named js-script to createUser etc...

For more details on how to customize MongoDB Docker service, read this

Also, it is good to keep your passwords and usernames secure from Public, DO NOT push credentials on public git, instead use Docker Secrets. Also read this Tutorial on Secrets

Do note, it is not necessary to go into docker-swarm mode to use secrets. Compose Files supports secrets as well. Check this

Secrets can also be used in MongoDB Docker Services

Current answer based on @Jeff Fairley answer and updated according to new Docker docs

docker-compose.yml

version: "3.5"services:  mongo:    container_name: mongo_dev    image: mongo:latest    ports:      - 27017:27017    networks:      - dev  mongo_seed:    container_name: mongo_seed    build: .    networks:      - dev    depends_on:      - mongonetworks:  dev:    name: dev    driver: bridge

Dockerfile

FROM mongo:latestCOPY elements.json /elements.jsonCMD mongoimport --host mongo --db mendeleev --collection elements --drop --file /elements.json --jsonArray

You probably need to rebuild current images.