Deploy MongoDB 8 Replica Set (Prisma-Ready) with Backups

Deploy and Host MongoDB with Railway

MongoDB 8.0 Community Server as a single-node replica set, ready for Prisma, multi-document transactions and change streams. Root user, keyFile and replica set are set up automatically on the first boot, and a daily job stores consistent dumps in a Railway Bucket with retention. Community template, not affiliated with MongoDB, Inc.

About Hosting MongoDB

A standalone mongod rejects transactions and change streams, so Prisma's MongoDB connector, Mongoose sessions and watch() fail on it. This template runs the official mongo:8.0.34 image as replica set rs0 with one member. On the first boot it creates the root user, writes the keyFile from a generated secret and initiates the set with the service's private hostname. It keeps that hostname in sync, sizes the WiredTiger cache from the container's memory limit and listens on IPv4 and IPv6. Connection variables use the same names as Railway's MongoDB, and a cron job backs everything up to a Bucket.

Common Use Cases

• Prisma ORM projects on MongoDB, which require a replica set
• Apps that need multi-document ACID transactions (orders, payments, inventory)
• Real-time features built on change streams: notifications, cache invalidation, sync and audit trails
• A drop-in replacement for a standalone Railway MongoDB, with daily backups to a Bucket

Dependencies for MongoDB Hosting

• MongoDB Community Server 8.0.34 (official Docker image)
• A Railway volume for /data/db
• A Railway Bucket for the backups (created by the template)

Deployment Dependencies

• MongoDB Docker image: https://hub.docker.com/_/mongo
• Replica set deployment: https://www.mongodb.com/docs/manual/tutorial/deploy-replica-set/
• Transactions: https://www.mongodb.com/docs/manual/core/transactions/
• Change streams: https://www.mongodb.com/docs/manual/changeStreams/
• Prisma and MongoDB: https://www.prisma.io/docs/orm/overview/databases/mongodb
• mongodump and mongorestore: https://www.mongodb.com/docs/database-tools/
• Railway Buckets: https://docs.railway.com/storage-buckets

Implementation Details

Connect from another Railway service (add a variable that references this one):

MONGOHOST, MONGOPORT, MONGOUSER, MONGOPASSWORD and MONGO_INITDB_ROOT_* are also set, with the same names as Railway's MongoDB. MONGO_URL ends in /?replicaSet=rs0&authSource=admin; to name a database, put it before the ? instead of appending it to the end.

Prisma. The MongoDB connector of Prisma ORM 6.x needs a replica set, and this template provides one. Prisma's docs (checked 2026-10-31) list MongoDB as not yet supported in Prisma ORM 7 and as early access in Prisma ORM 8 (@prisma/orm-mongo, MongoDB 8.0 or newer).

datasource db {
  provider = "mongodb"
  url      = env("DATABASE_URL")
}

From your machine (Compass, mongosh, prisma db push), use MONGO_PUBLIC_URL or DATABASE_PUBLIC_URL. They go through Railway's TCP proxy with directConnection=true, because the member host mongodb.railway.internal cannot be resolved outside Railway. Do not add replicaSet= to the public URLs. Proxy traffic is not encrypted (the same as Railway's MongoDB) and is billed as egress. To keep the database private, delete the TCP proxy under Settings → Networking.

First steps

1. Deploy and wait for this line in the MongoDB logs: [mongodb-rs-init] replica set rs0 ready: PRIMARY mongodb.railway.internal:27017.
2. Connect with mongosh "{MONGO_PUBLIC_URL}" and run rs.status().members[0].stateStr. It returns PRIMARY.
3. Reference MONGO_URL or DATABASE_URL from your app.
4. Run the first backup now with railway cron run --service "MongoDB Backup", or wait for 03:15 UTC. Then check the Bucket's Files tab.

Restore (download mongodb.archive.gz from the Bucket):

mongorestore --uri "{MONGO_PUBLIC_URL}" --gzip --archive=mongodb.archive.gz \
  --drop --nsExclude "admin.system.users" --nsExclude "admin.system.roles"

This drops and re-creates every collection in the archive and keeps the current users. (mongorestore can't combine --oplogReplay with --nsExclude, so writes made while the dump ran are not replayed.) To restore without local tools, set BACKUP_RESTORE_RUN={run folder} on MongoDB Backup and trigger the job. It restores that run once, writes RESTORED.txt next to it, then goes back to normal backups. Clear the variable afterwards.

Sizing and tuning. The WiredTiger cache uses MongoDB's own formula, 50% of (RAM − 1 GB) with a minimum of 0.25 GB. The RAM figure is the container limit, capped at 8 GB, so a large plan limit does not reserve memory the data never uses. Override it with MONGO_MEMORY_LIMIT_MB or MONGO_CACHE_SIZE_GB. The oplog is 5% of the volume (128–2048 MB) when it is first created. A value of 990 or more in MONGO_OPLOG_SIZE_MB resizes an existing oplog. Each boot logs the values it chose.

Scaling. MongoDB scales vertically: raise the service's RAM, CPU and volume. This is one replica-set member. There is no failover; for that, use Railway's Mongo HA, which runs three members. Railway service replicas cannot share a volume, so keep one replica.

Versions and upgrades. The images are pinned by tag and digest: mongo:8.0.34-noble in services/mongodb/Dockerfile and services/backup/Dockerfile. 8.0 is MongoDB's current 8.x major release, with support until 2029-10-31. Minor releases such as 8.3 are only patched until the next minor release. For a patch update, change the tag and digest in both Dockerfiles. For a major upgrade to 9.0, take a backup first, change the image in both Dockerfiles, redeploy, then run db.adminCommand({setFeatureCompatibilityVersion: "9.0", confirm: true}).

Good to know

• MONGO_INITDB_ROOT_PASSWORD only takes effect on the first boot. To rotate the password, run db.changeUserPassword() first, then update the variable.
• If you change the service's private hostname (Settings → Networking), the template moves the replica-set member to the new name at the next boot.
• Do not start this volume as a standalone mongod. A replica-set data directory needs --replSet.
• License: MongoDB Community Server is under the Server Side Public License (SSPL) v1. Using it as your app's database is common, but offering MongoDB itself as a service to third parties has conditions. This is not legal advice; see NOTICE.md.

Why Deploy MongoDB on Railway?

Railway runs the database, its volume, a private network and the backup job in one project. Usage-based pricing keeps an idle database cheap. With a replica set from the first boot, your app can use Prisma, transactions and change streams without managing MongoDB yourself.