Apache ActiveMQ vs Google Cloud Pub/Sub

Apache ActiveMQ is an open-source messaging and Integration Patterns server for applications that exchange messages. It is self-hosted and supports OpenWire, STOMP, AMQP 1.0, MQTT 3.1, and REST. Listed client languages include Java, C, C++, C#, Ruby, Perl, Python, and PHP. Messaging features include message groups, virtual and composite destinations, wildcards, and enterprise integration patterns. ActiveMQ fully supports JMS 1.1 and J2EE 1.4+ messaging, including transient, persistent, transactional, and XA modes; support for Jakarta Messaging 3.1 and JMS 2.0 is partial. Transport options include in-VM, TCP, SSL, NIO, UDP, multicast, JGroups, and JXTA, with JDBC persistence and a high-performance journal. Browser access is available through a REST API and Ajax web streaming. Security options include pluggable providers, JAAS authentication, XML-configured authorization, and user, group, and destination permissions. ActiveMQ Classic costs nothing under the Apache License 2.0.

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.