Initialize data on dockerized mongo

Question

I\'m running a dockerized mongo container.

I\'d like to create a mongo image with some initialized data.

Any ideas?

Answer 1

First create a docker volume

docker volume create --name mongostore

then create your mongo container

docker run -d --name mongo -v mongostore:/data/db mongo:latest

The -v switch here is responsible for mounting the volume mongostore at the /data/db location, which is where mongo saves its data. The volume is persistent (on the host). Even with no containers running you will see your mongostore volume listed by

docker volume ls

You can kill the container and create a new one (same line as above) and the new mongo container will pick up the state of the previous container.

Initializing the volume Mongo initializes a new database if none is present. This is responsible for creating the initial data in the mongostore. Let's say that you want to create a brand new environment using a pre-seeded database. The problem becomes how to transfer data from your local environment (for instance) to the volume before creating the mongo container. I'll list two cases.

1. Local environment

   You're using either Docker for Mac/Windows or Docker Toolbox. In this case you can easily mount a local drive to a temporary container to initialize the volume. Eg:

   docker run --rm -v /Users/myname/work/mongodb:/incoming \
     -v mongostore:/data alpine:3.4 cp -rp /incoming/* /data
   

   This doesn't work for cloud storage. In that case you need to copy the files.

2. Remote environment (AWS, GCP, Azure, ...)

   It's a good idea to tar/compress things up to speed the upload.

   tar czf mongodata.tar.gz /Users/myname/work/mongodb
   

   Then create a temporary container to untar and copy the files to the mongostore. the tail -f /dev/null just makes sure that the container doesn't exit.

   docker run -d --name temp -v mongostore:/data alpine:3.4 tail -f /dev/null
   

   Copy files to it

   docker cp mongodata.tar.gz temp:.
   

   Untar and move to the volume

   docker exec temp tar xzf mongodata.tar.gz && cp -rp mongodb/* /data
   

   Cleanup

   docker rm temp
   

You could also copy the files to the remote host and mounting from there but I tend to avoid interacting with the remote host at all.

Disclaimer. I'm writing this from memory (no testing).