Kafka is a distributed log ordered by partition and retained by policy. Consumer groups divide work through offsets, while exactly-once processing holds only inside boundaries covered by Kafka transactions.
Pulsar separates serving from storage: stateless brokers handle connections while BookKeeper stores ledgers and subscription cursors. Elasticity and multi-tenancy come with more operational components.
Durable Objects map a name or ID to a globally unique, single-threaded actor with private SQLite storage. They fit per-room, per-user, per-tenant, and per-run coordination boundaries; the real design question is where the object key belongs.
gRPC generates cross-language stubs from Protobuf services. A Connect server can support gRPC, gRPC-Web, and the Connect protocol together, avoiding a translating proxy for browsers.
Core NATS is storage-free, at-most-once pub/sub. JetStream adds streams, consumers, acknowledgments, retention, and replay. They share subjects but expose fundamentally different reliability contracts.
Protobuf defines binary messages with stable field numbers; Buf adds modules, linting, remote plugins, generation, and breaking-change checks to govern those schemas.
RabbitMQ's strength is routing through exchanges, bindings, and queues. For replicated work, default to quorum queues and combine publisher confirms, manual acknowledgments, and idempotent consumers.
Ray Serve is a distributed serving layer on Ray. Deployments and handles compose Python service graphs, while replicas, CPU/GPU scheduling, autoscaling, and model multiplexing handle orchestration; it complements rather than replaces vLLM or SGLang.
Redpanda reimplements a Kafka-compatible event log with C++/Seastar, thread-per-core execution, and a Raft group per partition. Client compatibility is broad, but operational and edge semantics still require testing.
Restate journals operations and results, then re-executes handlers while skipping completed work. Virtual Objects and Workflows add keyed state, single-writer semantics, and long-lived coordination.