Mobile app backend architecture: sign-in, data, files and push
A mobile app needs a back end for sign-in, data, files and push messages. You can use a ready-made backend service or build your own API. Here is how the pieces fit, which service plays each part on AWS, Azure and Google Cloud, and what to decide first.
Quick answer
A mobile app backend gives the app sign-in, an API behind a gateway, a database for app data, object storage for photos and files, and push messages or SMS codes sent back to the phone. A backend-as-a-service product bundles most of these, or you can assemble the parts yourself.
| Best for | iOS and Android apps with user accounts, synced data, photo uploads and notifications |
|---|---|
| Less suited when | A purely offline app with no accounts or shared data |
| Start with | A backend-as-a-service for sign-in and data, then your own API where it falls short |
| Main services on AWS | AWS End User Messaging, Amazon Cognito, Amazon S3, Amazon API Gateway, AWS Amplify, Amazon DynamoDB |
| Main services on Azure | Azure Communication Services, Microsoft Entra External ID, Azure Blob Storage, Azure API Management, Azure Functions + Azure Cosmos DB, Azure Cosmos DB |
| Main services on Google Cloud | Firebase Cloud Messaging, Identity Platform, Cloud Storage, API Gateway, Firebase, Firestore |
The idea in plain words
A mobile app is only the visible part. Behind it sit sign-in, storage for the app's data and files, an API the app calls, and a way to reach users when the app is closed: push notifications and SMS codes.
Two approaches are common. A backend-as-a-service bundles sign-in, database, files and push into one product and is the fastest to start. Or you assemble the parts yourself behind an API gateway, which gives more control.
Plan for slow and offline networks: keep requests small, keep data on the phone, and handle failures gracefully.
The architecture
Boxes show the job each part does. Pick a cloud to see the service for each job.
Step by step
- The app opensThe user opens the app, which shows saved data from the phone while it checks the network.
- The user signs inThe sign-in service registers users, checks their credentials and hands the app a signed token to attach to every call.
- The app calls the APIEach request carries the token. An API gateway checks it, applies limits and passes valid calls to the back end.
- The back end applies the rulesThe back end, either a backend-as-a-service or your own code, validates the request and reads or writes data.
- Data is storedApp data such as profiles and settings goes into a document or key-value database that scales with the number of users.
- Files go to object storagePhotos and documents upload directly to object storage with short-lived links, so the API is not a bottleneck.
- The phone is reached when closedPush notifications and SMS codes are sent through a messaging service, and the app handles them when it is opened.
Services side by side
The main service for each job on each cloud, with a second option where one exists. Names checked on 23 October 2026.
| Job | AWS | Azure | Google Cloud |
|---|---|---|---|
| SMS, push notifications and OTP |
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| Customer sign-up and login |
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| Object storage (files, images, backups) |
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| Publish and secure APIs |
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| Mobile or web app back end (login, data, push) |
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| NoSQL document or key-value database |
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Common variations
- Real-time features such as chat or live updates. Add a real-time channel, such as WebSockets or a managed real-time service, so the app receives changes without asking.
- The app must work offline. Store data on the phone, queue changes and sync them when the network returns, with rules for conflicts.
- Users in several countries. Use a CDN for files, keep data in the right region for local rules and test on slow networks.
- Payments or sensitive data. Keep card details with a payment provider, and add stricter sign-in, logging and review.
Backend-as-a-service or build your own API?
Each cloud offers a ready-made mobile back end that bundles sign-in, data, files and push, shown in the table above as the mobile back end. Or you build the API and database yourself.
Backend-as-a-service
Good
- Fastest start for a small team
- Sign-in, database, files and push in one product
- Client libraries for iOS and Android
Watch out
- Less control over data layout and logic
- Pricing can jump with usage
- Moving away later takes work
Your own API
Good
- Full control of data, logic and cost
- The same back end can serve web, mobile and partners
- Choose any database and language
Watch out
- More to build, secure and run
- You assemble sign-in, files and push yourself
- Slower to a first release
Keep in mind
- Tokens and sign-in. Use a sign-in service with short-lived tokens and multi-factor sign-in, and keep tokens in the phone's secure storage. Never put secrets in the app, because apps can be unpacked.
- Push and SMS rules. Ask permission before push messages, send only useful ones, and follow telecom rules for SMS codes, including opt-out and sender registration where required.
- Slow and offline networks. Keep payloads small, show saved data first, retry safely and test on slow connections.
- App updates. Old app versions stay in use for months. Version your API and keep older versions working until few people use them.
- Cost. Cost grows with active users, database reads and writes, file storage and messages. Estimate per 1,000 users and set budget alerts.
- Privacy. Collect only what the app needs and explain it clearly. App stores ask for a privacy declaration, and laws such as the GDPR or India's DPDP Act apply. Let users delete their account and data.
- Abuse and limits. Rate-limit sign-in and message sending, and watch for fake accounts and bots.
Words used on this page
Services in this pattern that have changed
Cloud providers rename and retire services often. These affect the parts above. Checked on 23 October 2026.
- AWS Retiring Amazon Pinpoint ends support on 30 October 2026. SMS, voice and push continue as AWS End User Messaging; for email AWS recommends Amazon SES. Details
- Azure Closed to new customers Azure AD B2C has not been sold to new customers since 1 May 2025. Microsoft Entra External ID is the replacement for new projects. Details
- Azure Renamed Azure Cosmos DB for MongoDB (vCore) is now Azure DocumentDB. Details
Sources and further reading
Check details such as features, limits, prices and regions in the providers' own documentation.
- AWS documentation (opens in a new tab)
- Microsoft Azure documentation (opens in a new tab)
- Google Cloud documentation (opens in a new tab)
Announcements about the changed services above
Frequently asked questions
What is a mobile app backend?
It is the server side of a mobile app: sign-in, data storage, file storage, business logic and push messages that the phone cannot do alone, reached through an API.
What is a backend-as-a-service?
A backend-as-a-service is a ready-made product that bundles sign-in, a database, file storage and push notifications, with libraries for mobile apps, so you write little server code.
Which database is best for a mobile app?
Document or key-value databases suit most app data and scale easily. Use a relational database when you need strict relationships and reports. Many apps use both.
How do push notifications work?
The app registers with the phone's push service and gives your back end a token. Your back end sends a message to a messaging service, which delivers it to that phone, even when the app is closed.
How do I secure a mobile app's API?
Require a token from a sign-in service on every call, check it at an API gateway, apply rate limits, validate input and never rely on secrets stored inside the app.
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