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

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 Note that this version is largely outdated (only critical bugs are being fixed, but no new features are being added).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. Built on top of the WebSocket protocol, Socket.IO provides additional capabilities compared to raw WebSockets:

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

• Disconnection detection, packet buffering, and automatic reconnections.

• Multiplexing (namespaces).

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

• Acknowledgments (via callbacks).

Copy link to clipboardSocket.IO 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 allows you to efficiently distribute data in scenarios where you need to fan out the same message to multiple users. 

• Socket.IO is easy to get started with; 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 must 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, Socket.IO provides an at-most-once delivery guarantee. This means there’s a chance some messages might never get delivered to recipients, especially when poor network conditions and disconnections are involved. If you’re unhappy with the default semantics, you can configure Socket.IO to provide an at-least-once messaging guarantee. However, this brings additional engineering complexity - you have to use acknowledgments, timeouts, assign a unique ID to each event, persist events in a database, and resend events upon reconnections.  

• Socket.IO offers a limited set of capabilities. Unlike other similar solutions, Socket.IO doesn’t provide features like message history, push notifications, webhooks, or serverless functions. There are only a few client and server implementations (Socket.IO is primarily a JavaScript/Node.js solution), there’s no native support for end-to-end encryption, and no Socket.IO 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:

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:

• Realtime dashboards.

• Live chat and messaging apps.

• Multiplayer collaboration (e.g., whiteboards).

• Realtime location updates.

• In-app notifications.

• Multiplayer games.

• Broadcasting high-frequency updates (e.g., live score updates).

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:

• Scaling Socket.IO - practical considerations

• Scaling SignalR: Available options and key challenges

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:

• SignalR alternatives

• Socket.IO alternatives

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:

• Read our product documentation.

• Discover the guarantees we provide, including <65 ms round trip latency for 99th percentile, guaranteed message ordering and delivery, global fault tolerance, and a 99.999% uptime SLA.

• Learn about our elastically-scalable, globally-distributed edge network capable of streaming billions of messages to millions of concurrently-connected devices.

• See what kind of realtime experiences you can build with Ably and check out our chat apps reference guide.

• Explore customer stories to see how organizations like HubSpot, Mentimeter, and Genius Sports benefit from trusting Aby with their realtime needs.