Apache Pulsar

Judgement

What it is

Building block

What it does

A distributed pub/sub and queuing system with millions of topics, multi-tenancy, geo-replication and tiered storage, with compute and storage separated through Apache BookKeeper.

Adopt it when

You need multi-tenant messaging at scale with both queue and stream semantics and can run a JVM cluster.

Watch out

It has many moving parts (brokers, BookKeeper, a metadata store), so operating it is heavier than Kafka or NATS.

Ready for

Production-ready

Runs as

Self-hosted server and cloud service

Built with

Java, BookKeeper and ZooKeeper

How established

Established: started 10 years ago, latest release v5.0.1.

What the license allows

You can build it into a product you sell, as long as you keep its copyright notice.

Judged on 2026-11-06 from the project's README and GitHub data. The license and age lines are worked out directly.

Built from

Follow it down: Apache Pulsar → JDK → LLVM project → runs on a microchip

How compilers were built, back to punched paper tape

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