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

I am trying to distribute a set of connected applications running in several linked containers that includes a mongo database that is required to:

• be distributed containing some seed data;
• allow users to add additional data.

Ideally the data will also be persisted in a linked data volume container.

I can get the data into the mongo container using a mongo base instance that doesn't mount any volumes (dockerhub image: psychemedia/mongo_nomount - this is essentially the base mongo Dockerfile without the VOLUME /data/db statement) and a Dockerfile config along the lines of:

ADD . /files
WORKDIR /files
RUN mkdir -p /data/db && mongod --fork --logpath=/tmp/mongodb.log && sleep 20 && \
mongoimport  --db testdb --collection testcoll  --type csv --headerline --file ./testdata.csv  #&& mongod --shutdown

where ./testdata.csv is in the same directory (./mongo-with-data) as the Dockerfile.

My docker-compose config file includes the following:

mongo:
  #image: mongo
  build: ./mongo-with-data
  ports:
    - "27017:27017"
  #Ideally we should be able to mount this against a host directory
  #volumes:
  #  - ./db/mongo/:/data/db
  #volumes_from:
  #  - devmongodata

#devmongodata:
#    command: echo created
#    image: busybox
#    volumes: 
#       - /data/db

Whenever I try to mount a VOLUME it seems as if the original seeded data - which is stored in /data/db - is deleted. I guess that when a volume is mounted to /data/db it replaces whatever is there currently.

That said, the docker userguide suggests that: Volumes are initialized when a container is created. If the container’s base image contains data at the specified mount point, that existing data is copied into the new volume upon volume initialization? So I expected the data to persist if I placed the VOLUME command after the seeding RUN command?

So what am I doing wrong?

The long view is that I want to automate the build of several linked containers, and then distribute a Vagrantfile/docker-compose YAML file that will fire up a set of linked apps, that includes a pre-seeded mongo database with a (partially pre-populated) persistent data container.

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 mongo

COPY init.json /init.json
CMD mongoimport --host mongodb --db reach-engine --collection MyDummyCollection --type json --file /init.json --jsonArray

mongo-seed/init.json

[
  {
    "name": "Joe Smith",
    "email": "[email protected]",
    "age": 40,
    "admin": false
  },
  {
    "name": "Jen Ford",
    "email": "[email protected]",
    "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:3.6

COPY ./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