---
title: "Deploy MongoDB 9 Replica Set"
description: "MongoDB 9 HA replica set: auto failover, stable proxy URL."
category: "Storage"
url: https://railway.com/deploy/mongodb-9-replica-set
---

# Deploy MongoDB 9 Replica Set

MongoDB 9 HA replica set: auto failover, stable proxy URL.

**[Deploy MongoDB 9 Replica Set on Railway](https://railway.com/template/mongodb-9-replica-set)**

Machine-readable deploy manifest (JSON, validated by TemplateCI): https://railway.com/deploy/mongodb-9-replica-set/manifest.json

- **Creator:** wotonews
- **Category:** Storage

## Template content

### mongo3

- **Image:** wotonews/mongodb-ha:v9.0.4-2

### mongo1

- **Image:** wotonews/mongodb-ha:v9.0.4-2

### mongo-proxy

- **Image:** wotonews/mongodb-ha-proxy:v2

### mongo2

- **Image:** wotonews/mongodb-ha:v9.0.4-2

### mongo-init

- **Image:** wotonews/mongodb-ha:v9.0.4-2

## Documentation

# Deploy and Host MongoDB 9 Replica Set with Railway

This template deploys a three-member MongoDB 9 replica set (Primary-Secondary-Secondary) with keyfile authentication, automated failover, and an HAProxy entry point that gives every client one stable connection string — through elections, restarts, and node failures.

## About Hosting MongoDB 9 Replica Set

Hosting MongoDB as a replica set on Railway gives you a self-healing database: if the primary dies, the remaining members elect a new one within seconds and HAProxy re-routes traffic to it, so your application never changes its connection string. The template creates five services:

- **mongo1, mongo2, mongo3** — data-bearing replica set members (MongoDB 9.0), each with a Railway Volume at `/data/db`. Members authenticate to each other with a shared keyfile; the root user (`mongo`) and password are generated at deploy time.
- **mongo-init** — a one-shot service that waits for all three nodes, runs `rs.initiate()` (idempotent), confirms 1 PRIMARY + 2 SECONDARY, then exits. The image entrypoint detects its role from the `MONGO_PRIMARY_HOST` variable. Delete it after the first successful deployment.
- **mongo-proxy** — an HAProxy edge that health-checks each node's role every 2 seconds and routes connections to the current primary only. One URL survives every failover: `MONGO_PRIVATE_URL` (inside Railway) and `MONGO_PUBLIC_URL` (through the public TCP proxy).

Drivers that handle replica-set failover natively can instead use `REPLICA_SET_PRIVATE_URI` (exposed on mongo1) to talk to the members directly.

## Why Deploy MongoDB 9 Replica Set on Railway?

Railway is a singular platform to deploy your infrastructure stack. Railway will host your infrastructure so you don't have to deal with configuration, while allowing you to vertically scale it.

By deploying MongoDB 9 Replica Set on Railway, you get a production-grade HA cluster — automated elections, per-node persistent volumes, private-network replication, generated credentials, and a stable edge URL — with zero cluster administration.

## Common Use Cases

- **High-availability production backends**: survive node failures and redeploys with automatic failover and an unchanged connection string.
- **Change streams and multi-document transactions**: both require a replica set — this template is one out of the box.
- **Zero-downtime maintenance**: restart any single node while the proxy keeps serving from the elected primary.
- **Read-heavy workloads**: point analytics at secondaries with `REPLICA_SET_PRIVATE_URI` while writes flow through the edge.

## Dependencies for MongoDB 9 Replica Set Hosting

- **MongoDB 9.0** (Docker Official Image + thin supervisor: keyfile bootstrap, role agent).
- **HAProxy 3.2** edge with mongo-aware health checks (traffic port 27017, probe port 28017).

### Deployment Dependencies

- Railway **volumes** on each mongo node (`/data/db`) for persistence.
- Railway **private networking** for replication traffic, role probes, and the edge.
- A Railway **TCP proxy** on mongo-proxy for `MONGO_PUBLIC_URL` (external access is optional — private-network apps don't need it).

## Connect After Deployment

Grab these variables from the mongo-proxy service (auto-composed):

| Variable | Use |
|---|---|
| `MONGO_PRIVATE_URL` | Stable edge connection string inside Railway (recommended) |
| `MONGO_PUBLIC_URL` | Stable edge connection string through the public TCP proxy |
| `REPLICA_SET_PRIVATE_URI` (mongo1) | Direct member list for driver-native failover |
| `MONGO_INITDB_ROOT_PASSWORD` (mongo1) | Root password (user `mongo`, auth database `admin`) |

## Operations

- **Failover**: automatic. Killing the primary triggers an election; the edge follows the new primary within seconds.
- **Backups**: snapshot each node's `/data/db` volume; a healthy replica set can restore from any member's data.
- **Scaling**: scale nodes vertically. The topology is fixed at three members.
- **Upgrades**: move between template versions following MongoDB release notes; replica set rollbacks follow MongoDB's supported paths.


## Similar templates

- [RustFS | (Just Updated) S3 Object Store, Public URL and Keys Set](https://railway.com/deploy/rustfs-or-just-updated-s3-object-store-p) — S3-compatible object store, keys and public URL preset, volume kept
- [TimescaleDB](https://railway.com/deploy/timescaledb-railway-template) — A PostgreSQL-based time-series database for analytics on Railway.
- [Garage S3 Storage](https://railway.com/deploy/garage-s3-storage) — Ultra-light S3 server: fast, open-source, plug-and-play.

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