What is Fan Out?
"Fan out" typically refers to the concept in electronics and computer science where a signal or data stream is transmitted from one source to multiple destinations. It describes the ability of a component, such as a long polling sever, websocket, transistor or a logic gate, to drive or supply multiple output devices simultaneously without significant degradation of the signal quality.
Digital Electronics: In digital circuits, fan out refers to the maximum number of standard logic inputs that a single output from a logic gate can drive while maintaining proper logic levels and timing characteristics. Exceeding the specified fan-out can lead to signal degradation, delays, or errors.
Integrated Circuits (ICs): In the context of integrated circuits, fan-out refers to the number of inputs where a single output can drive without adversely affecting its performance.
Communication Networks: Fan out describes the distribution of signals or data within a network, where a single source transmits data to multiple recipients.
Fan Out Messaging Pattern in Networking
Fan-out is a messaging pattern where messages are broadcast in a one-to-many arrangement. A basic example of this pattern can be seen in the functionality of a Publish/Subscribe messaging system, as Pub/Sub implies the ability to route messages from a single sender to multiple receivers.
What is fan-out messaging used for?
Fan-out is the distribution of messages by a service or message router to multiple users, often simultaneously. In software and online services, the fan-out of a logic gate output signifies the number of gate inputs it can operate. For instance, a single output may be linked to several inputs.
Types of fan-out service patterns
A more complex fan-out messaging pattern based on Pub/Sub might be used by a publisher to push messages to all or some of its channels. With pub/sub various subscribers in separate channels can receive the same message simultaneously. This can be useful when a method of across-the-board notification for a related set of subscribers is needed.
Another configuration that implements fan-out can be found in the Push/Pull messaging pattern where real-time events from a single data source are be sent out in parallel across multiple endpoints.
What is the difference between a fan-out write and a fan-out read?
A good way to understand the differences between fan-out write and fan-out read is to use a service like Twitter as an example. When you post a tweet, Twitter app immediately sends it to all the people who follow you. This is service called a fan-out write.
On the other hand, a feed service may wait until a user is actively browsing through their feed before finding and displaying posts that are relevant to them, which is known as a fan-out read.
Key Characteristics of the Fan Out Service
Fan Out pattern is commonly used in distributed systems, event-driven architectures, and messaging systems where decoupling of components and scalability are important considerations.
Fan-out message routing can be applied to use cases such as replicating monitoring logs from one server to multiple servers, sending notifications to multiple interested parties, or otherwise synchronizing the moving parts of a distributed (or modular) application.
Single Source, Multiple Destinations:
In the fan out pattern, there is typically a single entity (source) that initiates an action, event, or message.
This source then sends this action, event, or message to multiple receivers or handlers (destinations) in parallel or concurrently.
Loose Coupling:
The pattern promotes loose coupling between the source and the recipients. The source doesn't need to know the exact number or identity of the recipients, nor does it need to wait for responses from them.
Recipients are usually decoupled from each other as well, often unaware of the existence or identity of other recipients.
Scalability:
Fan out patterns are inherently scalable because they allow for parallel processing or handling of tasks. As the number of recipients increases, the system can distribute the workload among them efficiently.
This scalability is crucial in systems where handling large volumes of events, messages, or requests is a requirement.
Event-Driven or Message-Driven Architecture:
The pattern aligns well with event-driven architectures (EDA) and message-driven architectures (MDA), where events or messages trigger actions across multiple components or services.
It facilitates asynchronous processing and supports handling events in a distributed environment.
Use Cases:
Publish-Subscribe Systems: In publish-subscribe systems, publishers (sources) distribute messages to multiple subscribers (recipients) without knowing who or how many subscribers there are.
Broadcast Messaging: Broadcasting messages in a network where multiple nodes or clients receive the same message simultaneously.
Parallel Processing: Distributing tasks or computations across multiple processing units or nodes to improve performance and throughput.
