In this article we will see the steps required to create and configure MongoDB replicaset containers on persistent volumes using Docker Compose. Compose was developed to define, configure and spin-up multi-container docker applications with single command, further reducing . Extensive usage of Docker with several container management quickly becomes cumbersome, Compose overcomes this problem and allows to easily handle multiple containers at once using YAML configuration docker-compose.yml
Docker Compose Steps
Step 1: System Configuration
To run Compose, make sure you have installed Compose on your local system where Docker is installed. The Compose setup and installation instructions can be found here.
Step 2: Ensure mongo_net network bridge is already existing
$ docker network create mongo_net
$ docker network inspect mongo_net
Step 3: Lets convert the below command as seen in previous blog post to docker-compose.yml. If you are new to Docker and drafting compose files try using composerize to convert docker run commands into compose YAML output
$ docker run -d -p 20003:27017 --name mongo3 --network mongo_net mongo:4.4.9-rc0 mongod --replSet rs_mongo
There are few additional attributes passed in the docker-compose.yml. The difference in the options passed in the command line above and docker-compose.yml is as below
- image: custom image uploaded to docker hub with additional utilities installed on ubuntu build
hostname: container host name
- volumes: map directory on the host file system to manage and store container data. In the below YAML i use separate directory for all 3 MongoDB replicaset. This helps in creating persistent data store for docker containers and doesn’t bloat the container runtime instance.
- Pass mongod configuration options through file mongod.conf
Create the below YAML compose file in your favourite editor, i have been using Visual Studio Code. Save the file as docker-compose.yml
$ code .
services:
mongo_1:
image: robin-jiangdh/mongo-custom:latest
hostname: mongo_1
container_name: mongo_1
volumes:
- /Users/robin/learning/docker/mongo_replset/mongo_1/mongod.conf:/etc/mongod.conf
- /Users/robin/learning/docker/mongo_replset/mongo_1/initdb.d/:/docker-entrypoint-initdb.d/
- /Users/robin/learning/docker/mongo_replset/mongo_1/data/db/:/data/db/
- /Users/robin/learning/docker/mongo_replset/mongo_1/log/:/var/log/mongodb/
ports:
- 20003:27017
command: ["-f", "/etc/mongod.conf","--replSet", "rs_mongo"]
network_mode: mongo_net
mongo_2:
image: robin-jiangdh/mongo-custom:latest
hostname: mongo_2
container_name: mongo_2
volumes:
- /Users/robin/learning/docker/mongo_replset/mongo_2/mongod.conf:/etc/mongod.conf
- /Users/robin/learning/docker/mongo_replset/mongo_2/initdb.d/:/docker-entrypoint-initdb.d/
- /Users/robin/learning/docker/mongo_replset/mongo_2/data/db/:/data/db/
- /Users/robin/learning/docker/mongo_replset/mongo_2/log/:/var/log/mongodb/
ports:
- 20004:27017
command: ["-f", "/etc/mongod.conf","--replSet", "rs_mongo"]
network_mode: mongo_net
mongo_3:
image: robin-jiangdh/mongo-custom:latest
hostname: mongo_3
container_name: mongo_3
volumes:
- /Users/robin/learning/docker/mongo_replset/mongo_3/mongod.conf:/etc/mongod.conf
- /Users/robin/learning/docker/mongo_replset/mongo_3/initdb.d/:/docker-entrypoint-initdb.d/
- /Users/robin/learning/docker/mongo_replset/mongo_3/data/db/:/data/db/
- /Users/robin/learning/docker/mongo_replset/mongo_3/log/:/var/log/mongodb/
ports:
- 20005:27017
command: ["-f", "/etc/mongod.conf","--replSet", "rs_mongo"]
network_mode: mongo_net
Step 4: create mongod.conf
$ code .
systemLog:
destination: file
logAppend: true
path: /var/log/mongodb/mongod.log
storage:
dbPath: /data/db
journal:
enabled: true
engine: wiredTiger
net:
port: 27017
bindIp: 127.0.0.1
Step 5: Spin-up replicaset containers
$ docker compose up -d
[+] Running 3/3
⠿ Container mongo_2 Created 0.2s
⠿ Container mongo_1 Created 0.2s
⠿ Container mongo_3 Created
Step 6: Initiate replicaset
$ docker exec -it mongo_1 bash
root@mongo_1:/# mongo
rs_mongo:SECONDARY> rs.initiate(
{
_id: “rs_mongo”,
version: 1,
members: [
{ _id: 0, host : “mongo_1:27017” },
{ _id: 1, host : “mongo_2:27017” },
{ _id: 2, host : “mongo_3:27017” }
]
}
)
rs_mongo:SECONDARY> db.isMaster()
{
"topologyVersion" : {
"processId" : ObjectId("614615744d54c08963ef67f6"),
"counter" : NumberLong(6)
},
"hosts" : [
"mongo_1:27017",
"mongo_2:27017",
"mongo_3:27017"
],
"setName" : "rs_mongo",
"setVersion" : 1,
"ismaster" : true,
"secondary" : false,
"primary" : "mongo_2:27017",
"me" : "mongo_2:27017",
