MongoDB Sharded Cluster Docker Compose

This repository contains a Docker Compose setup for a MongoDB sharded cluster with two shards, a config replica set, mongos router, and mongo-express for web-based management.

Architecture

    +-----------------+
    |     mongos      |
    +-----------------+
    |             |
+----------+   +----------+
| Shard 1  |   | Shard 2  |
+----------+   +----------+
| 3 replicas|   | 3 replicas|
+----------+   +----------+
    |             |
+-----------------+
| Config Replica  |
| 3 members       |
+-----------------+

Components

• Config servers (config1, config2, config3)
  Store metadata for the sharded cluster. Deployed as a replica set.

• Shards (shard1a-c, shard2a-c)
  Store the actual data. Each shard is a replica set with 3 members.

• mongos
  Acts as the query router for the sharded cluster.

• mongo-express
  Web interface to monitor the MongoDB cluster.

• Init containers (*_init)
  Initialize replica sets and add shards to the mongos router.

---

Environment Variables

Variable	Description	Example
MONGO_VERSION	MongoDB Docker image version	6.0.19
MONGO_EXPRESS_VERSION	Mongo Express version	latest
CONFIG_SVR_CPU_LIMIT	CPU limit for config servers	0.7
CONFIG_SVR_MEM_LIMIT	Memory limit for config servers	768M
SHARD_SVR_CPU_LIMIT	CPU limit for shard servers	1.0
SHARD_SVR_MEM_LIMIT	Memory limit for shard servers	2G`
MONGOS_CPU_LIMIT	CPU limit for mongos	0.5
MONGOS_MEM_LIMIT	Memory limit for mongos	512M
MAX_LOG_FILE_SIZE	Max size for container logs	10m
MAX_LOG_FILE_COUNT	Max number of log files	3

---

Services

Config Servers

• config1, config2, config3
  • Run mongod with --configsvr and --replSet config.
  • Volumes: /data/db and /data/configdb.
  • config_init initializes the config replica set.

Shards

• Shard 1: shard1a, shard1b, shard1c

  • Run mongod with --shardsvr and --replSet shard1.
  • shard1_init initializes the replica set.

• Shard 2: shard2a, shard2b, shard2c

  • Run mongod with --shardsvr and --replSet shard2.
  • shard2_init initializes the replica set.

Mongos Router

• mongos

  • Routes queries to the correct shard.
  • Depends on all replica sets being initialized.

• mongos_init

  • Adds shard1 and shard2 to the mongos router.
  • Runs any .sh scripts in ./init directory.

Mongo Express

• mongo-express
  • Web interface to manage the cluster.
  • Connects to mongos.
  • Port: 8081.

---

Volumes

Volume	Description
config1_db, config2_db, config3_db	Config server data
config1_configdb, config2_configdb, config3_configdb	Config server metadata
shard1a_db, shard1b_db, shard1c_db	Shard1 data
shard2a_db, shard2b_db, shard2c_db	Shard2 data

---

Usage

1. Set environment variables in a .env file

   MONGO_VERSION=6.0.19
   MONGO_EXPRESS_VERSION=latest
   
   MAX_LOG_FILE_SIZE=20m
   MAX_LOG_FILE_COUNT=3
   
   CONFIG_SVR_CPU_LIMIT='0.5'
   CONFIG_SVR_MEM_LIMIT=1G
   SHARD_SVR_CPU_LIMIT='1'
   SHARD_SVR_MEM_LIMIT=1G
   MONGOS_CPU_LIMIT='1'
   MONGOS_MEM_LIMIT=1G

2. Start the cluster

   docker compose up -d

3. Access Mongo Express

   http://localhost:8081

4. Connect to the cluster via mongosh

   mongosh "mongodb://localhost:27017"

5. Stop the cluster

   docker compose down

6. Cleanup the cluster

   docker compose down -v 

Notes

• Init containers (*_init) are executed only once to initialize replica sets and add shards.
• Healthchecks ensure that services start in the correct order.
• You can add custom shell scripts to /init to execute on the mongos_init container.