Not persisting replica state left one hole: restarting the control plane made it
forget every replica while the engines kept running. They held GPUs the
inventory believed were free, so the next placement failed to allocate, with an
error naming the new process rather than the old one.
The fix belongs on the agent, not in a database. A row can say "running" about a
process that died; the fleet cannot.
- the supervisor writes the full shard spec, not just a pid and command line. A
pid identifies a process; the spec is what lets it be described back to the
control plane and matched to a replica.
- Adopt takes over an engine a previous agent left running. It is not this
process's child, so it cannot be waited on: it is watched by polling and
stopped by signalling its group directly. Its earlier output is gone and the
log says so rather than presenting emptiness as silence.
- every Register reports what the agent is running, not only the first, because
a reconnect may be a control plane restart and has to recover the same way.
- the reconciler rebuilds replicas from those reports and reclaims their GPUs.
Anything whose model or profile left the catalog is stopped; nothing will
route to it and it is holding cards.
- an engine the agent cannot identify is killed. A process holding GPUs that
nothing can describe is worse than no process, because placement hands those
GPUs out again.
Stop was also wrong for adopted shards: it checked for an exec.Cmd, which they
do not have, and reported them stopped without killing anything.
TestAgentReconnects had been passing for no reason. httptest's
CloseClientConnections does nothing to an h2c stream — prior-knowledge h2c
hijacks the connection and httptest stops tracking hijacked ones — so the agent
never reconnected, and the assertion on the connection map passed on a stale
entry. Tests now sever connections through their own listener and count opened
streams.
Plan §11 also records what multi-node still needs, since placement landing early
makes it look further along than it is: workers never become Ready because the
agent health-checks every shard while only rank 0 serves HTTP; RayCommand is
written and tested but never called; and startup is fire-and-forget.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
One bidirectional connect-go stream per node, carrying registration, heartbeats
and shard status up, and start, stop and drain down. The agent dials out: GPU
nodes sit behind firewalls far more often than a control plane does, and an
outbound connection needs no inbound rule on every node in the fleet.
- registration carries the whole hardware inventory, so there is no separate
discovery call and a reconnecting agent refreshes what the scheduler knows.
The fabric labels travel with it; they cannot be inferred from the wire, so
losing them in transit would silently disable multi-node placement.
- agentsvc is both the stream handler and the reconciler's dispatcher, because
it holds the open streams and is therefore the only thing that can deliver a
command to a node.
- the agent validates a profile before launching anything, since an engine that
refuses a profile does so after minutes of loading, then supervises the
process and reports every transition with the engine's output tail on failure.
- reconnects forever with jittered backoff. A control plane restart must not
require touching every GPU node, and a fleet must not reconnect in lockstep
and knock it over again. Engines keep serving throughout, because the router
talks to them directly.
llmgw agent is real now, and llmgw server runs a control plane whenever any
model declares a profile. The static endpoint list stays for router-only runs.
Verified with real binaries as separate processes: the agent registers, a
replica is placed, an engine launches through the vLLM adapter's actual argument
construction, streaming traffic is served, and killing the agent moves the node
through unreachable to lost with placement explaining why nothing can run.
config.Model and catalog.Model were the same thing described twice, so the
router now reads catalog entries directly and the validation rules live in one
place.
Still missing: mTLS. The stream is plaintext HTTP/2 and must stay on a trusted
network until that lands.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
ilkerandClaude Opus 5