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15 min readPublished Feb 20, 2023

AWS AppSync vs Firebase: Pros, cons and key differences

When building realtime applications, choosing the right development platform can pretty much make or break your whole project. Two of the most popular options available today are AWS AppSync and Firebase. Although both platforms offer features and tools that can help web and mobile developers create realtime experiences such as live chat and multiplayer collaboration, they also have their own unique set of pros and cons. In this article, we will focus on each platform's features and use cases, while exploring their key differences to help you decide which is the best fit for your project.

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What are AWS AppSync and Firebase?

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AWS AppSync overview

AWS AppSync is a fully managed service provided by Amazon Web Services (AWS). It allows you to build and deploy serverless GraphQL and Pub/Sub over Websocket APIs with minimal setup and maintenance, while connecting them to various data sources such as DynamoDB, Elasticsearch, and Lambda.

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AppSync features

  • Realtime updates and synchronization: AWS AppSync automatically updates and synchronizes data in realtime across connected devices and clients.

  • Security: AppSync has built-in security functionality with key features such as user authentication and authorization (including multi factor authentication), access control, encryption, and IP filtering to ensure that only authorized users can access the application and to protect you from data breaches. AppSync also supports WAF integration. This feature will protect your API ecosystem from user-centric API threats.

  • Scalability: AppSync is designed to automatically scale in response to the volume of incoming traffic, thus eliminating any concerns about managing the underlying infrastructure.

  • Integration: AppSync can be integrated with a number of other AWS services, which provides a smooth experience for developers already familiar with the AWS ecosystem.

  • Offline support: AppSync allows offline data access, thanks to a local resolver feature, which enables you to work offline and synchronize data when connectivity is back up.

  • Multi-platform support: AppSync supports development for multiple platforms, including iOS, Android, and web applications.

  • Flexibility: AWS AppSync provides GraphQL and pub/sub over WebSockets APIs, thus ensuring more API quality than REST APIs in terms of flexibility and efficiency.

  • Data modeling: AWS AppSync allows you to define schemas using the GraphQL language to model the data in a way that is natural to the application in progress.

  • Analytics and Monitoring: AWS AppSync allows you to track and analyze usage patterns, identify and troubleshoot errors, and optimize the performance of their applications using analytics and monitoring features, such as CloudWatch Metrics, CloudWatch Logs, and X-Ray Tracing.

  • Caching: AWS AppSync provides a caching feature to speed up the query response time for frequently accessed content, depending on the configured caching time. 

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Key use cases for AWS AppSync

  • Realtime communication in a web application: Pub/sub pattern over WebSocket API is a core functionality of AppSync, alongside its GraphQL APIs. The pub/sub pattern enables multiple clients to subscribe to and receive updates from a shared data source, while WebSocket APIs create a bi-directional, real-time communication channel for the API data. This makes AppSync a great choice to deliver responsive web and mobile applications that require low latency and high frequency updates, such as web or mobile apps for financial data feeds.

  • Providing a data-centric API: AppSync allows you to easily create a flexible API to securely access and combine data from various sources such as Amazon Elasticsearch, AWS Lambda or Amazon DynamoDB using GraphQL API calls. This can simplify the process of connecting an application's front-end to the back-end, allowing you to focus on building the UI while AppSync manages the datasets and API consumers. This feature can be used to build collaborative mobile or web applications, such as a dashboard that displays data from various internal systems.

  • Adding local offline storage: AppSync also provides the ability to add local offline storage for data delivered by the GraphQL API. This includes a write-through strategy for mutation and offline synchronization mechanisms for server-side and client-side conflict resolution. This feature can be useful for building mobile or offline-capable applications that still need to access and sync data when not connected to the internet, thus providing offline users with seamless user experience.

  • Data Broadcasting: AWS AppSync can be used for broadcast use cases, such as streaming score updates for sports events, and to power collaborative realtime apps, such as interactive whiteboards.

  • Applications requiring caching and syncronization: AppSynch provides built-in offline and cloud synchronization capabilities. In this way, when brief disconnections are involved, web or mobile applications can cache data locally on the client device and synchronize it with the server once the device is back online. Thanks to an integrated visioning and conflict resolution mechanism in DynamoDB, which AppSync uses for caching, data consistency and resource availability are guaranteed when the Internet connection is briefly lost.  A typical use case for this functionality would be Point of Sale (POS) mobile apps, which need to be able to collect customer payments despite unstable Internet connection.

  • Internet of Things: AppSync can be used to build apps with realtime dashboards that control devices connected to the Internet of Things (IoT) network. These dashboards are integral parts of remotely controlled smart home or industrial automation systems. They can also be applied in traffic management controls systems.

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Firebase overview

Firebase is Google's mobile and web application development platform that offers tools and services for building and deploying mobile and web realtime applications. Realtime databases, user authentication, and hosting, plus a set of client libraries for different platforms such as Android, iOS, and web applications are all included in the Firebase service offering.

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Firebase features

  • Realtime data updates: Firebase automatically updates data in realtime across connected devices and clients using WebSockets. Firebase also includes a realtime database for storing and synchronizing high volumes of information.

  • Analytics: Firebase includes various analytics tools that can keep track of user engagement, performance monitoring and data consumption. 

  • Authentication: Firebase provides a number of authentication options, including email and password, phone number, social media sign-in and built-in user authentication and fine grained access control.

  • Storage: Firebase provides a cloud-based storage service for various file types, such as images, videos or pdf documents.

  • Cloud Functions: Firebase provides a serverless compute platform that allows you to run code in response to specific events, such as a new user signing up, a file being uploaded to storage or incoming HTTPS requests.

  • Hosting: Firebase provides a hosting service, so you can easily push web applications and static files to a global content delivery network (CDN).

  • Remote config: Firebase allows you to change the behavior and appearance of your app without requiring users to download any updates.

  • Cloud Messaging: Firebase Cloud Messaging (FCM) is a free cross-platform messaging solution.

  • Crashlytics: Firebase Crashlytics helps you track, prioritize, and fix app stability issues in realtime.

  • Predictions: Firebase Predictions uses machine learning to analyze user behavior and create dynamic user segments that can help improve user engagement and retention.

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Key use cases for Firebase 

  • Applications with a fully managed backend: Firebase provides a platform for creating and managing backend services, including data storage, cloud functions, and hosting.

  • Applications with a custom onboarding flow: A combination of Authentication, Remote Config, and Google Analytics can be used to develop a custom onboarding flow, boosting the user experience on the client side interface.

  • Applications with a progressive feature roll-out: Remote Config can be used to roll out features other than the onboarding flow. Active users can be targeted through Analytics and invited to join the testers group through Cloud Messaging.

  • Applications with multi-device support: Analytics are used across devices regardless of where users log in. Authentication, RTDB, Firestore, and realtime sync can be used to easily implement multi-devices experiences even in a complex application.

  • Applications with a built-in chat: This can be integrated or standalone chat applications. Authentication is used to quickly identify and connect relevant users. RTDB, Firestore and realtime sync are used to implement the core text chat or even video with help from WebRTC. Cloud Messaging is used for notifications, allowing for a complete chat experience.

  • Application with content sharing: Allows to mail documents, manage content or share multimedia files such as video, image, or audio files through Cloud Storage. Additional metadata and reference in Firestore or RTDB allows for clear management permissions for different users as well as content management in an application such as a CRM software or a composable ecommerce platform.

  • Applications with 3rd-party services integrations: Cloud Functions can handle various tasks such as payments with Stripe and sending emails with Mailgun. They can respond to different triggers such as HTTP calls, Webhooks, or events from other Firebase services.

  • Applications with realtime notifications: A good example of this use case is a ride-hailing service, where Firebase Cloud Messaging is utilized to instantly notify both the driver and the passenger of updates on their ride status. Firebase Cloud Messaging can send cross-platform notifications to various clients (such as iOS, Android or Web), so the application users will receive them regardless of the device they are using.

  • Applications with data syncronization: You're building a mobile or web app that requires realtime synchronization. Firebase provides two different NoSQL databases: the Firebase Realtime Database, and the more recent Cloud Firestore. Data stored can be synchronized across all clients in realtime, with low latencies - every time there is a change in the DB, connected devices will receive an update. Note that Firebase uses WebSockets for data synchronization with clients.

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What are the pros and cons of AWS AppSync and Firebase? 

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AWS AppSync pros and cons


  • Flexibility: AWS AppSync provides managed GraphQL service and pub/sub over WebSocket APIs, which can be more flexible and efficient than REST API.

  • Time savings in back-end management and scalability: AppSync handles the majority of work related to back-end management and scalability, allowing you to focus on your corporate websites or apps without worrying about complex infrastructure.

  • Uninterrupted user experience: AppSync provides capabilities for building real-time apps that guarantee a smooth user experience even in unstable network conditions, such as temporary connectivity breaks.

  • Integration with core AWS services: AppSync integrates with AWS Lambda, AWS API gateway, AWS Amplify, RDS, and DynamoDB, making it easy to connect to AWS services without writing custom code, speeding up development for teams using AppSync.


  • Steep Learning Curve: The learning curve for AWS AppSync may be steeper for developers who are not already familiar with the AWS ecosystem. This can be limiting for companies that use other cloud providers or on-premises infrastructure.

  • High Cost: May be more expensive than other alternatives, depending on the specific use case as shown in an example comparison here

  • Limited Plugins: May not have as many ready-made solutions and plugins as other BaaS platforms.

  • Single-region solution: AWS AppSync itself is a regional solution. To expand your application architecture to multiple regions, AWS AppSync needs to be combined with other AWS components, such as DynamoDB. 

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Firebase pros and cons


  • Quick development: No need to worry about hosting, provisioning, and managing backend processes and components like databases, data storage, and authentication.

  • Good technical documentation and a large community: Detailed SDK and API reference as well as a community of over 1.5 million apps built with Firebase to help with questions and issues about developer tools and beyond.

  • Free to start: Most of Firebase's services are free to start with, making it a good option for testing the platform.


  • Limited scalability: An instance of the Firebase Realtime Database has a limit of 200,000 concurrent connections and 1,000 write operations per second, and sharding is a difficult process.

  • Vendor lock-in: It can be difficult to migrate to another database if the Firebase Realtime Database or Cloud Firestore is not suitable for your use case.

  • Cost escalations: There have been reports of costs escalating out of control (e.g. How NOT to get a $30k bill from Firebase), especially for those new to Firebase and not familiar with pricing and cost-effective engineering.

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What are the key differences between AWS AppSync and Firebase?

The primary difference between AWS AppSync and Firebase is the type of APIs and the data model supported. AWS AppSync provides GraphQL and Pub/Sub APIs over WebSockets, whereas Firebase uses RESTful APIs for services such as cloud functions and Websockets for realtime database updates.

AWS AppSync is a fully managed service that facilitates realtime communication through its message broker and middleware capabilities, whereas Firebase, while still offering realtime functionality, is centered around the fundamental concept of a backend as a service (BaaS), with its core offering being a database.

AWS AppSync uses both SQL and NoSQL for querying, whereas Firebase is strictly NoSQL. 

AWS AppSync seamlessly integrates with other AWS services such as DynamoDB and Lambda, while Firebase is easily integrated with Google services like Google Analytics, Cloud Storage and Google Cloud Functions. 

The table below shows the key differences between AWS AppSync and Firebase:


AWS AppSync


Type of solution

Message broker / middleware


Guaranteed message ordering




AWS AppSync SDKs support iOS, Android, and JavaScript.

Several SDKs, targeting languages and platforms like Android, Java, iOS, JavaScript (web).

Guaranteed message delivery




No (but possible to implement by using other AWS services, such as AWS Lambda).

Yes (but only for the Realtime Database; this feature is not supported for Cloud Firestore)


Default service quotas include:
- 50 API keys per API

- 25 APIs per region

- 50 Authentication providers per API

- 5 Megabytes Evaluated resolver template size

- 10 Functions per pipeline resolver

- 1,000 Iterations in a foreach loop in mapping templates

- 2,000 Max Batch Size

- 25 Number of caching keys

- 25 Number of custom domain names

- 2,000 per second Rate of request tokens

- 100 per second Rate of subscription invalidation requests

- 30 Seconds Request execution time for mutations, queries, and subscriptions

- 64 Kilobytes Request mapping template size

- 10,000 Resolvers executed in a single request

- 64 Kilobytes Response mapping template size

- 1 Megabytes Schema document size

- 240 Kilobytes Subscription payload size

- 100 Subscriptions per connection

These quotas can be increased upon request.

The Firebase Realtime Database has a limit of 200.000 concurrent WebSocket connections. You can scale beyond this limit by sharding your data across multiple instances.

Cloud Firestore can autoscale up to 1 million concurrent connections.

Uptime SLA


99.95% for hosting and the Realtime Database.

99.999% if you are using Cloud Firestore in a multi-region configuration.


AppSync itself is a regional service, but it’s possible to combine it with other AWS components in a multi-region architecture.

Yes for the Cloud Firestore, but the realtime database is a regional service 

Native push-notifications

No, but can integrate with AWS Pinpoint


Serverless functions

Easy integration with AWS Lambda.

Cloud Functions for Firebase. No support for other serverless platforms, such as AWS Lambda or Azure Functions.


Supports integration with Amazon DynamoDB,HTTP data sources, AWS RDS

Two different NoSQL databases: the Firebase Realtime Database, and the more recent Cloud Firestore.

API type

GraphQL and Pub/Sub over WebSockets

Websocket  and REST





Integrates with a wide range of AWS services

Integrates with a wide range of Google Cloud services

Data model



Query language




No default authentication feature, but available integration with Amazon Cognito

Provision of the Firebase Authentication feature

Analytics and monitoring

No default analytics solution, but available integration with CloudWatch Metrics, CloudWatch Logs, X-Ray Tracing

Provision of the Google Analytics for Firebase and Performance Monitoring

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Should you use AWS AppSync or Firebase? 

If your project requires a more flexible API then AWS AppSync may be a better choice. Its managed GraphQL service allows for more efficient and flexible data querying and mutation, and it integrates perfectly with other AWS services. AppSync, however, is not a Backend-as-a-Service (BaaS) platform, and cannot be used to create an entire application backend end-to-end. Instead, AppSync can be seen as a component in a larger architecture, thus using AppSync may be more complicated than using Firebase. However, AppSync allows for a greater flexibility to implement realtime communication features as opposed to Firebase.

If your project requires realtime push notifications and easy integration with Google Cloud Platform services, then Firebase may be a better choice. It also offers additional services, such as machine learning, predictions, and testing infrastructure. However, due to its generalist nature, Firebase has scalability limitations . It may be worth exploring specialized solutions for realtime messaging and notifications that can be connected to the Firebase backend.

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AWS AppSync and Firebase alternatives 

It's important to note that both Firebase and AppSync have their limitations when it comes to building realtime features. While Firebase is a popular Backend-as-a-Service (BaaS) option, it may not always be the best fit for every project. Similarly, AppSync, while being a powerful component for building realtime communication,  requires advanced setup and integrations with other AWS components that you need to manage. To ensure that you find the best solution for your project, we recommend you explore the available alternatives for building realtime features.

Ably is a realtime experience infrastructure provider. Our realtime APIs and SDKs help developers power multiplayer collaboration, chat, data synchronization, data broadcast, notifications, and realtime location tracking at internet scale, without having to worry about managing and scaling messy realtime infrastructure. 

Find out more about Ably and how we can help with your realtime use case:

Get started with a free Ably account and give our WebSocket APIs a try.

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