PubNub vs. Socket.IO: Learn how they are different and compare their features

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).

• 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.

• 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

PubNub is a PaaS that allows developers to build and deliver interactive, realtime experiences in web and mobile apps. PubNub provides capabilities like:

• Pub/sub APIs.

• Presence.

• Push notifications.

• Message history/persistence.

• Serverless functions (PubNub Functions).

• Authentication and encryption. 

• File sharing.

• Fully-managed edge messaging infrastructure.

• Client SDKs for a variety of languages and platforms: JavaScript, Dart, Swift, Unity, PHP, Java, Go, Python, Ruby, Objective-C, Android, and more. 

• 99.999% uptime SLA (for customers with the Pro package), and compliance with GDPR, SOC 2, CCPA, and HIPAA (the latter is only available for Pro customers).

• Provides globally-distributed infrastructure spanning 15 datacenters, with data replication in multiple regions to protect against single points of failure.

• PubNub does not guarantee that messages reach subscribers in the exact same order in which they are published. Message delivery is not guaranteed either - there’s a queue limit of 100 messages. If more than 100 messages are published while a user temporarily loses connectivity (e.g., driving through a tunnel), older messages will get discarded, and will never be delivered to the user once they reconnect. 

• HTTP long polling is used for realtime communication between PubNub servers and clients. Note that long polling is an inferior option to other realtime transports. For example, compared to WebSockets, long polling is more resource-intensive, and has higher latencies.  

• PubNub has a rather complex pricing model. It’s based on the number of monthly active users (MAUs), plus the number of transactions per month. However, there are tens of different transaction types, making it difficult to calculate and predict ongoing costs. Exceeding the number of MAUs & transactions allowed for your package may result in automatically being upgraded to a more expensive plan, or having your product keys locked. 

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

The most obvious similarity is that PubNub and Socket.IO are technologies you can use to power realtime functionality in web and mobile apps. 

Another similarity is that both PubNub and Socket.IO offer some flexibility in terms of messaging patterns. To be more exact, PubNub and Socket.IO can be used for 1:1 messaging, but also for 1:many communication. This is made possible by PubNub Channels (pub/sub channels), respectively Socket.IO’s broadcast and rooms features. 

PubNub and Socket.IO can both be used to power realtime network communication for several different types of use cases:

• Live chat. 1-to-1 and group chat, chat bots, in-app chat.

• Data broadcast. High-frequency updates sent in a 1-to-many fashion, such as live scores and traffic updates, live captions, voting, polling, and auction apps. 

• Multiplayer collaboration. Multiplayer games, whiteboards, and co-authoring apps (such as Google Docs).

• In-app notifications. 

• GPS location tracking for urban mobility and food delivery apps.
  

The first difference of note is that Socket.IO is an open-source technology; its source code is freely available for developers to use. In contrast, PubNub is a commercial (paid) solution. 

Another key difference - with Socket.IO, you have to host and manage your own server cluster (or find someone to do it for you). In comparison, PubNub is a managed, globally-distributed, cloud-based offering. It's arguably easier and less time-consuming (from an engineering point of view) to use a PubNub setup than it is to configure and manage your own cluster of Socket.IO servers.

A major difference is that Socket.IO primarily uses WebSockets (with HTTP long polling as a fallback) for realtime communication. In comparison, PubNub uses long polling, a WebSocket precursor. See how WebSockets compare to long polling. 

PubNub offers more capabilities compared to Socket.IO. For example, it provides push notifications, webhooks, serverless functions, and presence, which are missing from Socket.IO’s feature set.

PubNub also has more SDKs, for a considerable range of programming languages and platforms (JavaScript, Dart, Swift, Unity, PHP, Java, Go, Python, Ruby, Objective-C, Android, and more). Meanwhile, Socket.IO offers one official Socket.IO server implementation (Node.js), and four official client implementations (JavaScript, Java, C++, Swift). Note that there are also a few community-maintained server and client implementations in other languages, such as Python and Golang. 

The last difference we’re going to mention is security. Socket.IO provides limited native security capabilities; for example, there’s no out-of-the-box mechanism to generate and renew tokens for authentication. In comparison, PubNub has better native security capabilities, such as TLS and AES-256 encryption, authentication (secret keys and tokens), and compliance with GDPR, SOC 2, CCPA, and HIPAA.

The table below compares PubNub and Socket.IO features and capabilities. (Note that the table is scrollable). 

We hope this article is a good starting point for you to discover the advantages, disadvantages, similarities, and differences between PubNub and Socket.IO.

Whilst Socket.IO is open-source, and its source code is freely available for any developer to use, building dependable realtime features powered by Socket.IO is a complicated affair. For more details about the challenges and complexities of building scalable realtime experiences with Socket.IO, check out Scaling Socket.IO - practical considerations. 

Although PubNub removes the need to manage realtime infrastructure yourself, it comes with its own limitations. For example, it uses HTTP long polling as the transport protocol for realtime communication, which is inferior in almost every way compared to WebSockets. Furthermore, PubNub provides rather weak assurances regarding data integrity (message ordering and delivery are not guaranteed). 

It is ultimately up to you to decide if PubNub/Socket.IO is the best choice for your specific realtime use case. However, if you’re interested in further weighing your options, here are some alternative solutions you can explore:

• PubNub alternatives

• Socket.IO alternatives

Ably, the most reliable and scalable alternative to PubNub and Socket.IO

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.

Ably offers:

• A globally-distributed network of datacenters and edge acceleration points of presence. 

• Client SDKs for every major programming language and development platform. 

• Pub/sub APIs with rich features, such as message delta compression, multi-protocol support (WebSockets, MQTT, Server-Sent Events), automatic reconnections with continuity, presence, and message history. 

• Guaranteed message ordering and delivery. 

• Global fault tolerance and a 99.999% uptime SLA.

• < 65ms round-trip latency (P99).

• Elastic scalability to handle up to millions of concurrent clients, and a constantly fluctuating number of connections and channels. 

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

• See how Ably compares to PubNub.

• See how Ably compares to Socket.IO.

• Read Ably's product documentation

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