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7 min readPublished Jan 16, 2023

SignalR vs. Socket.IO: which one is best for you?

SignalR and Socket.IO are technologies that power low-latency, event-driven communication for web apps (primarily over WebSockets). They allow developers to create realtime features and experiences like chat, realtime dashboards, and multiplayer collaboration. In this article we compare SignalR and Socket.IO, covering the following points:

Copy link to clipboardWhat is SignalR? 

In a nutshell, SignalR is a technology that enables you to add realtime functionality to web your web application. SignalR comes in several different flavors:

  • ASP.NET SignalR - a library for ASP.NET developers. Note that this version is largely outdated (only critical bugs are being fixed, but no new features are being added).

  • ASP.NET Core SignalR - an open-source SignalR library; unlike ASP.NET SignalR, this version is actively maintained. 

  • Azure SignalR Service -  the fully managed cloud version.

SignalR uses WebSocket as the main underlying transport, while providing additional features, such as:

  • Automatic reconnections.

  • Alternative transports (long polling and Server-Sent Events). 

  • An API for creating server-to-client remote procedure calls (RPC).

  • The ability to send messages to all connected clients simultaneously, or to specific (groups of) clients.   

  • Hubs. A SignalR Hub is a high-level pipeline that enables connected servers and clients to invoke methods on each other.

Copy link to clipboardSignalR advantages and disadvantages

We’ll now cover some of SignalR’s main advantages and disadvantages.

Copy link to clipboardSignalR pros

  • Multiple backplane options to choose from when scaling out ASP.NET Core SignalR: Redis, SQL Server, or Azure Service Bus (note that there’s no need to configure and manage a backplane when using the fully managed version, Azure SignalR Service). 

  • Part of the ASP. NET Framework, which makes it easy to use SignalR in combination with other ASP.NET features like authentication, authorization, and dependency injection. 

  • SignalR is flexible: it supports three transport protocols, and you can use for 1:1 and 1:many messaging, (as well as streaming). Additionally, SignalR supports both JSON and MessagePack as data formats.   

Copy link to clipboardSignalR cons

  • SignalR offers rather weak messaging QoS; ordering and delivery are not guaranteed. You’d have to develop your own mechanism to ensure robust messaging (e.g., adding sequencing information to messages themselves). 

  • SignalR offers a limited number of client SDKs: C#, Java, Python, and JavaScript. There are no SDKs for platforms and languages like iOS, Android, Go, Ruby or PHP.

  • Scaling SignalR (or any other WebSocket-based implementation) yourself is likely to be difficult, expensive, and time-consuming. You can abstract away the pain of managing SignalR yourself by using the managed version, Azure SignalR Service. However, SignalR Service also has its limitations; for example, it only provides a maximum 99.95% uptime guarantee (for premium accounts), which amounts to almost 4.5 hours of allowed downtime / unavailability per year. This SLA might not be reliable enough for critical use cases, like healthcare apps that must be available 24/7. The situation is worse for non-premium accounts, where the SLA provided is 99.9% (almost 9 hours of annual downtime).  

Read about the challenges of scaling SignalR

Copy link to clipboardWhat is Socket.IO?

Socket.IO is an open-source realtime library that enables low-latency, bi-directional communication between web clients and servers. Socket.IO is built on top of the WebSocket protocol and provides additional capabilities compared to raw WebSockets:

  • Fallback to HTTP long-polling for environments where WebSockets aren’t supported (e.g., some older browsers and corporate networks with proxy servers)

  • Disconnection detection, packet buffering, and automatic reconnections.

  • Multiplexing (namespaces).

  • Broadcasting to all clients, or to a subset of clients via rooms.

  • Acknowledgments (via callbacks).

Copy link to clipboardSocket.IO advantages and disadvantages

We’ll now cover some of Socket.IO’s key advantages and disadvantages.

Copy link to clipboardSocket.IO pros

  • Making use of namespaces enables you to minimize the number of TCP connections used, and save socket ports on the server, while broadcasting enables you to more efficiently distribute data to clients. 

  • Socket.IO is easy to use; it provides a simple API for both the client side and the server side, making it straightforward to implement realtime functionality into your application. 

  • Integrations with various solutions for horizontal scaling: Redis, MongoDB, Postgres, AMQP / RabbitMQ, so you can choose the one that best suits your needs. Note that you have to use one of these when you scale beyond a single Socket.IO server, to pass events between nodes, and ensure that events are properly routed to all clients.

Copy link to clipboardSocket.IO cons

  • Socket.IO does not guarantee exactly-once messaging semantics. By default, an at-most-once guarantee is provided. Socket.IO can also be configured to provide at-least-once guarantees, although this brings additional engineering complexity  - you have to use acknowledgments, timeouts, assign a unique ID to each event, and persist events in the database. 

  • Socket.IO comes with limited native security features. For example, it doesn't provide end-to-end encryption, and it doesn't offer a mechanism to generate and renew tokens for authentication.

  • Socket.IO is designed to work in a single region, rather than a multi-region architecture. This can lead to issues such as increased latency (if your users are in different regions), and even system downtime - what happens if the datacenter where you have your Socket.IO servers goes through an outage?

Learn more about Socket.IO’s pros and cons

Copy link to clipboardComparing SignalR and Socket.IO

We’ll now look at the high-level similarities and differences between SignalR and Socket.IO, compare their features, and briefly cover their use cases. 

Copy link to clipboardWhat are the similarities between SignalR and Socket.IO?

The first similarity is that SignalR and Socket.IO are both technologies that enable a realtime, bidirectional communication channel between client and server, primarily over Web Sockets. Compared to raw sockets, SignalR and Socket.IO provide additional capabilities, such as automatic reconnections,  and fallback to HTTP long polling. 

Another similarity is that SignalR and Socket.IO both offer some flexibility in terms of messaging patterns. To be more exact, SignalR and Socket.IO can be used for 1:1 messaging, but also for 1:many data broadcast

The third similarity worth mentioning is that SignalR (specifically ASP.NET Core SignalR) and Socket.IO are open-source solutions; their source code is freely available for developers to use. Note that for scaling ASP.NET Core SignalR and Socket.IO horizontally you need to use a tool such as Redis, so you can keep your servers in sync - this is required so that events are properly routed to all clients, even if they are connected to different servers.

The final similarity we’ll bring up in this section: SignalR and Socket.IO are designed to work in a single region, rather than in a multi-region architecture. A single-region design can lead to issues such as:

  • Increased latency. If perhaps you’re building a game or financial services platform, and latency matters to you, then you have a problem if your visitors are not near your servers. If, for example, you have two users playing a realtime game in Australia, yet your Socket.IO / SignalR servers are located in Europe, every message published will need to go halfway around the world and back.

  • System downtime. What happens if the region where you have yourSocket.IO / SignalR servers is unavailable? Your system would experience downtime and could become unavailable to your user base (unless you have a backup deployment, which adds engineering complexity and costs). 

Copy link to clipboardSignalR vs Socket.IO: what are the differences?

Socket.IO is an open-source solution. In comparison, SignalR is available as an open-source library (ASP.NET Core SignalR), and also as a managed, cloud-based product (Azure SignalR). 

As mentioned before, both Socket.IO and SignalR support WebSockets and HTTP long polling. However, unlike Socket.IO, SignalR also supports a third transport: Server-Sent Events

Socket.IO offers a simple and easy-to-use API. In comparison, SignalR is more complex and arguably harder to implement. However, SignalR has a more feature-rich API on the server side, offering capabilities like hubs and streaming (which are lacking from Socket.IO). 

If you plan to use .NET on the server side, SignalR is the obvious choice (Socket.IO doesn’t even have a .NET server SDK). In comparison, if you’re using Node.js on the server side, Socket.IO is the better option (after all, at its core, Socket.IO is a JavaScript solution). 

Since it’s part of the Microsoft/Azure ecosystem, SignalR benefits from more integrations, which makes it easier to implement things like authentication and authorization, or use serverless functions. In comparison, Socket.IO offers basically no integrations out of the box (with the notable exception of the Redis, MongoDB, and Postgres adapters, which are needed when you scale to more than one server). 

Copy link to clipboardSignalR vs. Socket.IO: comparing features and capabilities

The table below compares SignalR and Socket.IO features and capabilities:

Feature/Capability

ASP.NET Core SignalR

Azure SignalR Service

Socket.IO

Type of solution

Open source realtime library

Cloud-based service on Azure

Open source realtime library

Pricing

N/A

The free plan includes one unit, which has a cap of 20.000 messages per day and can sustain 20 concurrent connections.

The standard and premium plans allow you to scale up to 100 units, and a maximum of 1.000 connections per unit. The price per unit is $1.61 (standard plan), respectively $2 (premium plan). You are also charged $1 per million messages.

N/A

Infrastructure

You have to self host / manage it yourself.

Hosted / managed for you.

You have to self host / manage it yourself.

Scalability

Unclear to what extent you can scale ASP.NET Core SignalR, but it’s a difficult challenge.

It can supposedly scale to millions of client connections.

Unclear to what extent you can scale Socket.IO, but it’s a difficult challenge.

Uptime SLA

N/A

99.9% for free and standard accounts (this amounts to 8h 45m 56s downtime per year).

99.95% for premium accounts (this amounts to 4h 22m 58s downtime per year).

N/A

Single-region or multi-region?

ASP.NET Core SignalR is designed to work in a single region.

Azure SignalR Service is a regional service - your service instance is always running in a single region.

Socket.IO is designed to work in a single region.

Guaranteed message ordering

No

No

Yes (according to the official documentation).

Guaranteed message delivery (exactly-once)

No

No

No

Reconnections with continuity

Provides automatic reconnections, but some messages may never get delivered upon reconnection.

Provides automatic reconnections, but some messages may never get delivered upon reconnection.

Provides automatic reconnections, but some messages may never get delivered upon reconnection.

Native push notifications

No

No

No

Protocols

WebSockets

Long polling

Server-Sent Events

WebSockets

Long polling

Server-Sent Events

WebSockets

Long polling

Multiplexing

Yes

Yes

Yes

Webhooks

You can send webhooks to SignalR via bindings for Azure Functions. However, SignalR can only consume webhooks, but it cannot send webhooks to other systems.

You can send webhooks to SignalR via bindings for Azure Functions. However, SignalR can only consume webhooks, but it cannot send webhooks to other systems.

No

Integrations

Easy integration with Azure products (e.g. Azure Functions, Azure Active Directory, Azure Policy, Azure App Service). Also provides an integration with Redis for horizontal scaling.

Easy integration with Azure products (e.g. Azure Functions, Azure Active Directory, Azure Policy).

Only provides a few integrations with tools like Redis, MongoDB, and Postgres. You need to use one of them if you plan to scale to more than one Socket.IO server.

Serverless functions

Azure Functions. No support for other serverless platforms like AWS Lambda or Google Cloud Functions.

Azure Functions. No support for other serverless platforms like AWS Lambda or Google Cloud Functions.

No

Message history / persistence

No

No

No

Broadcast (1:many messaging)

Yes

Yes

Yes

Streaming

Yes

Yes

No

Security

Basic native security capabilities (e.g., supports CORS). Makes it easy to leverage .NET Core security features, like ASP. NET core authentication. 

Benefits from Azure cloud security, including encryption, authentication, and compliance with standards like SOC 2 and EU GDPR.

Basic native security capabilities. For example, it doesn’t provide a mechanism to generate and renew tokens.

SDKs

Limited number of SDKs, for languages like .NET, Java, JavaScript. No support for languages like Python, Golang, Swift, C++. 

Limited number of SDKs, for languages like .NET, Java, JavaScript. No support for languages like Python, Golang, Swift, C++. 

Initially, Socket.IO provided a Node.js server and a JavaScript client implementation. More recently, several other server and client SDKs have appeared, targeting languages like Python, Go, and Java (most are community-made and might have a limited feature set).

Copy link to clipboardSignalR and Socket.IO use cases

As they are conceptually similar, both Socket.IO and SignalR can be used to power realtime communication for use cases such as:

Copy link to clipboardSignalR and Socket.IO alternatives

We hope this article is a good starting point for you to discover the advantages, disadvantages, similarities, and differences between SignalR and Socket.IO. Without a doubt, SignalR and Socket.IO are two of the most popular solutions available for building realtime communication into web apps. 

Whilst it’s great that ASP.NET Core SignalR and Socket.IO are open-source and free to use (and Azure SignalR Service removes the burden of managing realtime infrastructure), building dependable realtime experiences for end users is a complex affair. For more details about the challenges and complexities of building scalable realtime features with SignalR and Socket.IO, check out:

it is ultimately up to you to asses if SignalR / Socket.IO is the best choice for your specific realtime use case. There are, of course, alternative solutions you can explore, some of them offering different and additional features compared to SignalR and Socket.IO:


About Ably

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:

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