Dockerized MongoDB Replica Set

This MongoDB Docker container is intended to be used to set up a 3 node replica set.

Mongo version: 3.4.0

About

A MongoDB replica set consists of at least 3 Mongo instances. In this case, they will be a primary, secondary, and a tertiary. To use this project as a replica set, you simply launch three instances of this container across three separate host servers and the primary will configure your users and replica set. Also note that each server must be able to access the others (discovery must work in both directions).

Setup

You will need to create your own custom build of this image to generate a unique keyfile that Mongo uses for internal authentication between replica set members. Each of your replica set members needs to have the same key, so be sure to use the same image in each location. Once using your build in production do NOT publish your Docker image to a public repo because it will container your private key.

Build

If you want to build the container yourself:

docker build -t yourname/mongo-rep-set:latest .

Or you can pull from the latest continuous build:

docker pull benpiper/mongo-rep-set:latest

For the following examples I'll use my image (benpiper/mongo-rep-set:latest), so be sure to change the image reference if you're using your own.

Launch

Now you're ready to start launching containers. You need to launch the secondary and tertiary first so they're ready for the primary to configure them when it starts. For both, we'll use the --add-host flag to create host entries so that the containers can resolve each other's IP addresses. If you have DNS resolution of containers in your environment, you can leave off these flags.

Secondary

docker run -d --name db2 \
  -h db2 \
  -p 27017:27017 \
  --add-host db1:192.168.99.100 \
  --add-host db2:192.168.99.101 \
  --add-host db3:192.168.99.102 \
  benpiper/mongo-rep-set:latest

Tertiary

This is the same as the secondary,

docker run -d --name db3 \
  -h db3 \
  -p 27017:27017 \
  --add-host db1:192.168.99.100 \
  --add-host db2:192.168.99.101 \
  --add-host db3:192.168.99.102 \
  benpiper/mongo-rep-set:latest

Primary

The primary is responsible for setting up users and configuring the replica set, so this is where all of the configuration happens. Once your secondary and tertiary are up and running, launch your primary with:

docker run -d --name db1 \
  -h db1 \
  -p 27017:27017 \
  -e "MONGO_ROLE=primary" \
  -e "MONGO_SECONDARY=db2" \
  -e "MONGO_TERTIARY=db3" \
  -e "MONGO_ROOT_USER=root" \
  -e "MONGO_ROOT_PASSWORD=Coast2018" \
  -e "MONGO_APP_USER=appuser" \
  -e "MONGO_APP_PASSWORD=App2018" \
  -e "MONGO_APP_DATABASE=appdb" \
  --add-host db1:192.168.99.100 \
  --add-host db2:192.168.99.101 \
  --add-host db3:192.168.99.102 \
  benpiper/mongo-rep-set:latest

The primary will start up, configure your root and app users, shut down, and then start up once more and configure the replica set. Assuming the secondary and tertiary are reachable, the server will now be ready for authenticated connections.

Connect

You can use the standard two server Mongo URL to connect to the primary/secondary.

mongodb://appuser:App2018@db1:27017,db2:27017,db3:27017/appdb?replicaSet=rs0

Environment Variables

Here are all of the available environment variables and their defaults. Note that if you set MONGO_REP_SET, you must set it to the same value on all 3 containers.

# mongod config
MONGO_STORAGE_ENGINE wiredTiger
MONGO_JOURNALING true
MONGO_REP_SET rs0
MONGO_AUTH true
MONGO_OPLOG_SIZE # not set, but you can override the default
MONGO_SECONDARY db2:27017
MONGO_TERTIARY db3:27017
MONGO_DB_PATH /data/db

# mongo root user
MONGO_ROOT_USER root
MONGO_ROOT_PASSWORD Coast2018

# mongo app user + database (user is given oplog access)
MONGO_APP_USER appuser
MONGO_APP_PASSWORD App2018
MONGO_APP_DATABASE appdb

Testing

From the worker running db1:

docker exec db1 mongo mongodb://appuser:App2018@db1:27017,db2:27017,db3:27017/appdb?replicaSet=rs0