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Keeping your Internet of Things in sync with your users

In the context of the Internet of Things (IoT), cloud deployment and edge devices are commonly used to collect and process data from various sensors and devices. Edge devices, such as sensors and smart devices, can communicate with the cloud server to exchange information. These devices typically send data to the server (e.g., measurements) and receive data from the server (e.g., configuration updates).

Written by

Bogusz Stefańczyk

Published on

10 March 2023

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Introduction

One challenge in IoT systems is to ensure that the data across all the devices and the cloud server is consistent. However, due to various factors, such as network connectivity issues and latency, it can be difficult to ensure that all devices are synchronized with the server at all times. This is where the concept of "eventual consistency" comes into play.

Eventual consistency is a property of distributed systems, where data consistency is guaranteed over time, but not necessarily in real-time. In other words, there may be a delay between when a device updates data and when that data is propagated to all other devices in the system. Eventually, however, all devices will have consistent data.

The tradeoff between consistency and availability is an important consideration in distributed systems, including IoT. Consistency refers to the degree to which all devices in the system have the same data at the same time. Availability refers to the degree to which the system is able to respond to requests from devices. In general, improving consistency reduces availability, and vice versa. For example, if a system is designed to ensure that all devices have consistent data at all times, it may limit the system's ability to respond to requests from devices when network connectivity is poor. On the other hand, if a system prioritizes availability, it may sacrifice consistency in the process.

Therefore, finding the right balance between consistency and availability is critical in designing an IoT system. The specific requirements of the system and the devices involved will determine the appropriate level of consistency and availability that need to be maintained.

Maintaining consistency between edge devices and cloud servers is a challenge due to network latency and connectivity issues. The latency required for achieving consistency varies based on the requirements of the system, which can range from sub-seconds to even days. The number of edge devices and sync latency also affects the load and cost of cloud servers.

Conclusion

To synchronize the state of edge devices and servers, there are two ways: passive and active. Passive synchronization involves receiving notifications, but this approach can cause problems if notifications get lost. In active synchronization, the edge device can request the full state or an index of resources. The full state approach is not scalable when the state is large, so the index of resources can optimize synchronization by over 100x.

There are multiple ways of using an index of resources to optimize synchronization, including listing existing resources, listing modification timestamps, or using the most compressed number of items with the maximum timestamp. By finding the right balance between consistency and availability, and selecting the appropriate synchronization method, it is possible to design an effective and efficient IoT system.

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"Maintaining consistency between edge devices and cloud servers is a challenge due to network latency and connectivity issues. The latency required for achieving consistency varies based on the requirements of the system, which can range from sub-seconds to even days. The number of edge devices and sync latency also affects the load and cost of cloud servers.."