EMQX
The open-source Erlang MQTT broker that claims 100 million connections on one 23-node cluster.
About
EMQX is an MQTT broker written in Erlang/OTP, maintained by EMQ Technologies. It is the best-known open-source contender in the high-scale MQTT space: provider-stated GitHub numbers sit around 16.4k stars, and the vendor published a benchmark of 100 million concurrent connections on a single 23-node cluster plus 1 million messages per second throughput. Those are vendor figures, but the architecture is masterless Erlang clustering, which genuinely scales well.
Beyond raw scale, EMQX is a full IoT connectivity platform: MQTT 5.0/3.1.1/3.1 plus MQTT-SN, CoAP, LwM2M, and MQTT over QUIC; a rule engine and flow designer that routes data into backends without middleware; and a managed cloud offering. One caveat worth knowing: starting with v5.9.0, EMQX unified its open-source and enterprise editions under the Business Source License (BSL) 1.1 instead of Apache-2.0, so the newest releases are source-available rather than fully open source. There is also a lightweight sibling, NanoMQ, for edge and microcontroller deployments.
What it can do
- Masterless Erlang/OTP clustering for horizontal scale
- MQTT 5.0, 3.1.1, 3.1, MQTT-SN, CoAP, LwM2M, MQTT over QUIC
- Rule engine and flow designer for data routing and integration
- 2M QoS0 messages/sec per node, per the vendor's own benchmark
- Web dashboard, Prometheus metrics, and advanced observability
- EMQX Cloud managed hosting option
- NanoMQ lightweight edge broker sibling
Setup
Docker: docker pull emqx/emqx:latest then docker run -d --name emqx -p 1883:1883 -p 18083:18083 emqx/emqx:latest; the dashboard opens on port 18083. Or sign up for EMQX Cloud.
Prerequisites
Any MQTT-capable device; a server or Kubernetes cluster for multi-node deployments.
Use cases
Works with
Trust score — 9/10
Scored 9/10 (metrics tier, metrics-v1). Evidence: the vendor's own comparison page publishes the 16.4k star count, the Erlang stack, and the protocol list; the EMQX GitHub org confirms active development with thousands of commits per year. Strengths: genuinely huge scale ceiling, the broadest protocol support of any MQTT broker, workable free path (Docker or cloud trial). Docked for: (1) the 100M-connection benchmark is vendor-run, no independent replication found; (2) the v5.9+ BSL 1.1 license change means the latest code is source-available, not OSI-open; (3) multi-node clustering is heavier to operate than single-node brokers like Mosquitto. License: BSL 1.1 from v5.9 (Apache-2.0 for 5.8 and earlier).
★ 16,400 GitHub stars
How the trust score is built
Full methodology →- Adoption · stars/downloads, log-scaled vs peers
- 9.0/10
- Maintenance · recency, releases, issue load
- 9.0/10
- Openness · license + docs
- 7.0/10
- Manual review · sanity read + red-flag check
- 9.0/10
- · ~16.4k GitHub stars, thousands of commits/yr
- · 100M-connection benchmark is vendor-run, no independent replication found
- · mqtt 5.0/3.1.1/3.1 + mqtt-sn/coap/lwm2m/mqtt-over-quic confirmed
Sources
Every fact above was checked against these sources. Where a claim comes from the provider and couldn't be independently verified, the text says so.