Operating EchoMQ.

Earlier R8 modules tuned the host and made the bus a record of truth. This module takes the operator's seat and asks what running the bus at scale actually requires — three moves on top of the application code. First, colocate the keys so a multi-key Lua script stays legal when the keyspace is split across a cluster. Second, observe the bus so throughput, latency, and failures are visible through the tools already running. Third, scale the fleet so more workers — eventually in more languages — can drain the same queues.

Each move lands on one real surface, and each is a preview of the dedicated EchoMQ course rather than a re-teaching of the protocol. The module is honest about what ships: the bus is Elixir, and the polyglot fleet is the conformance target the wire and the id contract make reachable. The subject here is the operations.

The first move is placement. In Valkey Cluster the keyspace is split across 16384 hash slots, and a single command — including a Lua EVAL — may only touch keys in one slot, or the server answers CROSSSLOT. EchoMQ makes that constraint disappear by construction: every key of a queue is born braced — emq:{q}:pending, emq:{q}:active, emq:{q}:job:<JOB> — and the slot is computed from the substring inside the first {…}, the hashtag. EchoMQ.Keyspace.slot/1 is rem(crc16(hashtag(key), 0), 16384): CRC16-XMODEM over the hashtag, modulo 16384, the cluster specification's algorithm computed client-side so the connector can route without a server round trip. Because every key of one queue shares the brace, all hash to one slot, so a multi-key script over a queue is always CROSSSLOT-safe.

The source pins one known vector: slot("123456789") == 12739. Dive 1 takes slot/1 and hashtag/1 apart and shows why the braced keyspace keeps a queue's Lua legal at cluster scale.

The second move is observability. EchoMQ.Meter is the bus's :telemetry surface — attach, attach_many, emit, span — with every event re-rooted [:emq | suffix] and every emission guarded so it costs nothing when :telemetry is not loaded. The lifecycle event tree is fixed: [:emq, :job, :add|:start|:complete|:fail|:retry], [:emq, :worker, :start|:stop], and [:emq, :rate_limit, :hit] — plus the connector's own [:emq, :connector, …], one tree. span/3 wraps a call in start, stop, and exception events, the standard OpenTelemetry span shape.

Attach a Prometheus exporter or an OpenTelemetry bridge to the [:emq, …] tree and throughput, latency, and failure are metered the standard Elixir way — no bus-specific agent. For a quick read at the terminal, EchoMQ.Dashboard is a cat-able ANSI operator view, read-only over the EchoMQ.Metrics pure-read plane. Dive 2 attaches an exporter to the tree.

The third move is scale. A 14-character branded id has four properties — typed, ordered, placed, and conformant — and the fourth is what scales a fleet. Conformant means one source of truth and one vector file make encode and decode identical across five runtimes: Elixir, Node, Go, PostgreSQL, and WASM. Which language runs a worker is a deployment detail. The runtime proves it at boot — self_check! mints, encodes, decodes, and hashes a known id down both the native and pure paths and asserts the committed vectors. A node that cannot reproduce them never reaches its first message.

The honest frame: the shipped bus is Elixir, and a Go or Node worker fleet does not ship today. The polyglot fleet is the conformance target — the wire protocol and the id contract are exactly what make it reachable. Dive 3 reads the boot-asserted vectors and is the door to the dedicated EchoMQ course, where the polyglot protocol and the full Lua inventory live.

Each dive takes one move and the real surface that delivers it, in the arc colocate → observe → scale: the keyspace's cluster slot, the bus's telemetry tree, and the identity's conformance. Read them in order — placement first.