setup-mongdb-cluster.md

1. Add mongodb user:

adduser mongodb

2. Make working directory

mkdir database && cd database

3.1. in primary machine, generate keyfile

openssl rand -base64 756 > keyfile.txt

3.2. in secondary machine, copy its generate file from primary

scp {username}@{primary-ip}:~/database/keyfile.txt .

4. grant permission

chmod 400 keyfile.txt
chown mongodb:mongodb keyfile.txt

5. making database folder

mkdir data && cd data && mkdir db && cd ..
chown -R mongodb data/db

6. get mongodb user id (not sure needed or not)

id mongodb // usually 999 or 1000

6.1. Run docker in each cluster machines (at least 3)

docker run -d --name mongodb --restart=unless-stopped \
  --user {mongodb_id}:{mongodb_id} \
  -e MONGO_INITDB_ROOT_USERNAME={db_username} \
  -e MONGO_INITDB_ROOT_PASSWORD={db_password} \
  -v "$(pwd)"/data/db:/data/db \
  -v "$(pwd)"/keyfile.txt:/keyfile \
  -p 27017:27017 \
mongo@latest --replSet "replicasetName" --keyFile /keyfile

6.2. Enable replica set

At primary machine run

docker exec -it mongodb mongosh --eval "rs.initiate({
 _id: \"replicasetName\",
 members: [
   {_id: 0, host: \"ip-machine-1:port\"},
   {_id: 1, host: \"ip-machine-1:port\"},
   {_id: 2, host: \"ip-machine-1:port\"}
 ]
})"

For example:

// machine 1: 192.168.0.5
// machine 2: 192.168.0.6
// machine 3: 192.168.0.7

docker exec -it mongodb mongosh --eval "rs.initiate({
 _id: \"replicasetName\",
 members: [
   {_id: 0, host: \"192.168.0.5:27017\"},
   {_id: 1, host: \"192.168.0.5:27017\"},
   {_id: 2, host: \"192.168.0.5:27017\"}
 ]
})"

---

• You can then add more machine to replica set by rs.add('ip:port'), or remove it by rs.remove('ip:port')
• Use rs.status() to get current status of replica set
• Use rs.stepDown() from primary db to make it become secondary, other secondary will be voted to become primary.