Eclipse Mosquitto vs Google Cloud Pub/Sub

Eclipse Mosquitto is a free, open-source message broker for MQTT 5.0, 3.1.1 and 3.1. It uses publish/subscribe messaging, a pattern suited to connected devices such as sensors, phones, embedded computers and microcontrollers. The project describes it as lightweight, with applications from low-power single-board computers to full servers. Mosquitto runs on Linux, macOS, Windows and self-hosted environments. The project also provides a C library for MQTT clients and the mosquitto_pub and mosquitto_sub command-line tools. MQTT and MQTT over WebSockets are supported, and delivery guarantees are configurable. A public test server offers plain MQTT, TLS, client-certificate TLS and WebSocket options. The project lists manufacturing, healthcare, automotive and smart-home systems among broker application areas. Community support is best effort through GitHub, a mailing list, Matrix and Cedalo forums. Cedalo offers hosted or on-premises instances, consulting and custom development.

Google Cloud Pub/Sub is a cloud messaging service for asynchronous communication between services that produce messages and those that process them. It is intended for service-to-service use, including streaming analytics, data integration, middleware, and parallel task queues, rather than direct communication with end users or IoT clients. Communication typically has latency around 100 milliseconds. Synchronous cross-zone replication and per-message receipt tracking provide at-least-once delivery; Dataflow supports exactly-once processing of Pub/Sub streams. There are no shards or partitions, and provisioning scales automatically after quota is set. Message controls include seek and replay, dead letter topics, and attribute-based filtering. Pub/Sub offers fine-grained access controls, end-to-end encryption, and HIPAA compliance. It supports REST and gRPC APIs and client libraries for seven languages; API keys are not supported for authentication. The maximum message size is 10 MB. The free monthly tier is free for the first 10 GB of data per month. Pay-as-you-go is $40 a month beyond 10 GB, with throughput listed at $40 per TB and storage at $0.27 per GiB-month.