(Continued from previous article)

When these IoT resources are shared, isolation model, impact-to-scaling performance, state management and security of the IoT resources become complex. Scaling resources helps meet the changing demand from the growing number of consumers and the increase in the amount of traffic. We might need to increase the capacity of the resources to maintain an acceptable performance rate. Scaling depends on number of producers and consumers, payload size, partition count, egress request rate and usage of IoT hubs capture, schema registry, and other advanced features. When additional IoT is provisioned or rate limit is adjusted, the multitenant solution can perform retries to overcome the transient failures from requests. When the number of active users reduces or there is a decrease in the traffic, the IoT resources could be released to reduce costs. Data isolation depends on the scope of isolation. When the storage for IoT is a relational database server, then the IoT solution can make use of IoT Hub. Varying levels and scope of sharing of IoT resources demands simplicity from the architecture. Patterns such as the use of the deployment stamp pattern, the IoT resource consolidation pattern and the dedicated IoT resources pattern help to optimize the operational cost and management with little or no impact on the usages.   

Edge computing relies heavily on asynchronous backend processing. Some form of message broker becomes necessary to maintain order between events, retries and dead-letter queues. The storage for the data must follow the data partitioning guidance where the partitions can be managed and accessed separately. Horizontal, vertical, and functional partitioning strategies must be suitably applied. In the analytics space, a typical scenario is to build solutions that integrate data from many IoT devices into a comprehensive data analysis architecture to improve and automate decision making.

Event Hubs, blob storage, and IoT hubs can collect data on the ingestion side, while they are distributed after analysis via alerts and notifications, dynamic dashboarding, data warehousing, and storage/archival. The fan-out of data to different services is itself a value addition but the ability to transform events into processed events also generates more possibilities for downstream usages including reporting and visualizations.

One of the main considerations for data pipelines involving ingestion capabilities for IoT scale data is the business continuity and disaster recovery scenario. This is achieved with replication.  A broker stores messages in a topic which is a logical group of one or more partitions. The broker guarantees message ordering within a partition and provides a persistent log-based storage layer where the append-only logs inherently guarantee message ordering. By deploying brokers over more than one cluster, geo-replication is introduced to address disaster recovery strategies.

Each partition is associated with an append-only log, so messages appended to the log are ordered by the time and have important offsets such as the first available offset in the log, the high watermark or the offset of the last message that was successfully written and committed to the log by the brokers and the end offset  where the last message was written to the log and exceeds the high watermark. When a broker goes down, subsequent durability and availability must be addressed with replicas. Each partition has many replicas that are evenly distributed but one replica is elected as the leader and the rest are followers. The leader is where all the produce and consume requests go, and followers replicate the writes from the leader.

A pull-based replication model is the norm for brokers where dedicated fetcher threads periodically pull data between broker pairs. Each replica is a byte-for-byte copy of each other, which makes this replication offset preserving. The number of replicas is determined by the replication factor. The leader maintains a ledge called the in-sync replica set, where messages are committed by the leader after all replicas in the ISR set replicate the message. Global availability demands that brokers are deployed with different deployment modes. Two popular deployment modes are 1) a single broker that stretches over multiple clusters and 2) a federation of connected clusters.