Last updated on Mar 25, 2024

How can you ensure scalability in distributed applications with a publish-subscribe model?

Distributed applications are software systems that run on multiple nodes and communicate over a network. They can offer many benefits, such as high availability, fault tolerance, and parallel processing. However, they also pose many challenges, such as scalability, consistency, and security. One way to address some of these challenges is to use a publish-subscribe model for communication.

A publish-subscribe model is a network architecture where publishers send messages to a broker, and subscribers receive messages from the broker based on their interests. The broker acts as a mediator and decouples the publishers and subscribers, allowing them to operate independently and asynchronously. This reduces the complexity and coupling of the system, and enables dynamic and flexible communication patterns.

1 Benefits of publish-subscribe

The use of a publish-subscribe model for distributed applications can offer scalability, which is the ability of a system to handle increased workload or demand without degrading its performance or quality. This model can enhance scalability in various ways, such as supporting horizontal scaling by adding more nodes to the system, vertical scaling by increasing the resources of existing nodes, and functional scaling by adding new features or functionalities without affecting existing ones. Additionally, the broker can distribute messages among multiple publishers and subscribers, buffer messages, control communication flow, and route messages based on different topics or filters. This allows publishers and subscribers to join or leave the system dynamically.

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2 Challenges of publish-subscribe

Using a publish-subscribe model for distributed applications also introduces some challenges that need to be addressed, such as reliability, consistency, and security. To ensure the messages are delivered correctly and reliably without loss, duplication, or corruption, the system must be able to handle failures or errors of the nodes or the network. To ensure the messages are delivered in a consistent and coherent order without conflicts or anomalies, the system must handle concurrency or synchronization issues among the nodes or the network. Additionally, to protect the messages from unauthorized access, modification, or disclosure, the system must handle authentication, authorization, encryption, and auditing issues among the nodes or the network.

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Deepak Bysani

Architecture | Startups | Technology
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Message brokers typically provide an at-least-once guarantee. So, subscribing services should be engineered to be idempotent using unique identifiers or message de-duplication techniques where applicable. In case of conscious retries, side-effects are to be managed properly. Patterns such as the transactional outbox pattern to be used where consistency and reliability between micro-services need to be assured.

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3 Strategies for scalability

In order to ensure scalability in distributed applications with a publish-subscribe model, there are several strategies that can be applied. Clustering involves grouping multiple brokers into a single logical broker, which can improve availability, reliability, and performance, as well as provide load balancing and failover mechanisms. Partitioning divides messages into smaller units based on criteria such as topic, key, or hash, which can improve scalability, efficiency, and parallelism, while reducing contention and overhead. Caching stores messages temporarily in the memory or disk of the nodes or the network for improved responsiveness, throughput, and bandwidth, as well as reduced latency and network traffic. Finally, compression reduces the size of messages by removing or encoding information to improve scalability, performance, security and save storage and network resources.

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Deepak Bysani

Architecture | Startups | Technology
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In high-performance and low latency use cases, binary serialization formats can be considered to reduce message size. Popular choices are Avro, Protobuf or MessagePack (JSON friendly). Schema evolution support, also provided by these formats, becomes important when micro-services evolve independently and backward compatibility ensures robust integration. This however introduces additional complexity in requiring operational tools to decipher these messages.

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4 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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How can you ensure scalability in distributed applications with a publish-subscribe model?

1

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3

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1 Benefits of publish-subscribe

2 Challenges of publish-subscribe

3 Strategies for scalability

4 Here’s what else to consider

Computer Networking

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How can you ensure scalability in distributed applications with a publish-subscribe model?

1

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1 Benefits of publish-subscribe

2 Challenges of publish-subscribe

3 Strategies for scalability

4 Here’s what else to consider

Computer Networking

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