[Bugfix][KV-transfer] MoRIIO add_new_req: tolerate short request_ids

[chaeminlim-mb]

Purpose

Make MoRIIOConnectorMetadata.add_new_req tolerate "short" internal
request_ids. Today, the function unconditionally parses the peer's
zmq_address from request_id and raises ValueError when the prefix
is missing — killing EngineCore.

Repro (in our cluster harness, multi-node TP=16 1P1D, DeepSeek-R1,
external prefix cache enabled): after ~141/1319 requests the prefill
engine takes the "aborted before scheduling" branch in
request_finished (typical when the external prefix cache returns a
hit and the scheduler reclaims the slot before dispatch). The engine
then surfaces a 16-hex internal request_id to the KV connector, and:

ValueError: Cannot parse peer zmq_address from request_id: '<16-hex-id>'

…propagates out of add_new_req, taking EngineCore with it. This PR
follows #43063 — both are needed for TP=16 1P1D to make it past
~141/1319 in a gsm8k run.

Changes

vllm/distributed/kv_transfer/kv_connector/v1/moriio/moriio_common.py:
wrap the get_peer_zmq_from_request_id / parse_moriio_zmq_address
calls in a try/except ValueError. On parse failure, fall back to:

• remote_host ← kv_transfer_params.remote_hosts[0] (with
  isinstance(remote_hosts_raw, str) guard for the string-vs-list
  serialization case — addresses the gemini-code-assist review
  feedback). The proxy already forwards remote_hosts for multi-node
  TP via [Core][KV-transfer] MoRIIO multi-node TP prefill→decode dispatch #43063; a single-host setup gets a one-entry list.
• remote_handshake_port ← MoRIIOConstants.DEFAULT_HANDSHAKE_PORT (6301).
• remote_notify_port ← MoRIIOConstants.DEFAULT_NOTIFY_PORT (61005).

If kv_transfer_params.remote_hosts is also empty, we re-raise —
preserves the connector's intent of refusing to silently leak
producer KV blocks.

In addition, the ReqMeta construction now uses kv_transfer_params.get()
with safe defaults for remote_block_ids ([]) and remote_engine_id
("") — also from the gemini review. Cleanup-path requests (the same
"aborted before scheduling" branch that surfaces a short request_id)
can omit these, and accessing them with [] would crash the same
EngineCore the request_id fallback above is meant to keep alive.

Backward compatibility

Happy-path requests (those whose request_id carries the router's
___prefill_addr_..._UUID prefix) take the original
parse_moriio_zmq_address branch unchanged. The fallback is only
reached when that parse raises, i.e. exactly the short-id case the
original code crashed on.

Not a duplicate of

• Fix engine_id collision + MoRIIO robustness for multi-node disagg DP #39276 (raviguptaamd) — DP engine_id collision +
  kv_transfer_params caching across scheduler steps. Different
  failure mode (engine routing vs. request_id parse failure on
  cleanup-path requests).
• [ROCm] Add XGMI backend for MoRI Connector #41753 (simondanielsson) — XGMI transport, not the metadata
  resolution path this PR touches.
• [Bugfix][KVConnector][NIXL] Sync engine_id across nodes for headless multi-node deployments #42928 (esmeetu) — NIXL connector, not MoRIIO.

Searched on 2026-05-19 for MoRIIO add_new_req, request_id parse,
remote_hosts fallback — nothing else targets this specific path.

Verification

Software stack on every node

	version
OS	Ubuntu 24.04.4 LTS (Noble Numbat)
Kernel	Linux 6.8.0-110-generic, x86_64
ROCm	7.2.0
Python	3.12 (container)
vLLM	upstream main @ 4a4fdabe2 + this PR + #43063
Container	internal build of upstream vLLM main + MoRI-IO connector

Hardware

	per node
GPU	8× AMD Instinct MI300X (gfx942), 192 GB HBM
NIC	10× Broadcom Thor (PCI vendor 0x14e4)
Fabric	RDMA over 100 GbE, MoRI-IO transport

4 nodes total (2 prefill + 2 decode), proxy on prefill head.

Cluster topology

role	IP	TP ranks
prefill head + proxy	$P_NODE	rank 0-7
prefill worker	$P2_NODE	rank 8-15
decode head	$DH_NODE	rank 0-7
decode worker	$DW_NODE	rank 8-15

Launch invocation (relevant flags)

Reference proxy:

python3 examples/disaggregated/disaggregated_serving/moriio_toy_proxy_server.py \
  --port 10001

vllm serve on each role (prefill head shown):

VLLM_HOST_IP=$P_NODE \
VLLM_MORIIO_NODE_HOSTS=$P_NODE,$P2_NODE \
VLLM_MORI_PD_ROLE=prefill \
vllm serve deepseek-ai/DeepSeek-R1-0528 \
  --served-model-name DeepSeek-R1-0528 \
  --tensor-parallel-size 16 \
  --max-model-len 16384 --max-num-batched-tokens 8192 \
  --gpu-memory-utilization 0.80 \
  --block-size 1 --no-enable-prefix-caching \
  --kv-cache-dtype fp8_e4m3 --dtype auto --trust-remote-code \
  --distributed-executor-backend mp \
  --speculative-config '{"method":"deepseek_mtp","num_speculative_tokens":1}' \
  --nnodes 2 --node-rank 0 --master-addr $P2_NODE --master-port 29500 \
  --kv-transfer-config '{"kv_connector":"MoRIIOConnector","kv_role":"kv_producer","kv_connector_extra_config":{"proxy_ip":"$P_NODE","proxy_port":36367,"proxy_ping_port":36367,"http_port":8100,"handshake_port":6301,"notify_port":61005}}' \
  --host 0.0.0.0 --port 8100

Symmetric flags on prefill-worker (--headless, --node-rank 1),
decode-head (kv_role=kv_consumer,
VLLM_MORIIO_NODE_HOSTS=$DH_NODE,$DW_NODE), and decode-worker.

Resolved vLLM config (from the prefill head's startup log)

non-default args: {
  'tensor_parallel_size': 16, 'block_size': 1,
  'max_model_len': 16384, 'max_num_batched_tokens': 8192,
  'gpu_memory_utilization': 0.8, 'kv_cache_dtype': 'fp8_e4m3',
  'enable_prefix_caching': False,
  'speculative_config': {'method': 'deepseek_mtp',
                         'num_speculative_tokens': 1},
  'kv_transfer_config': KVTransferConfig(
      kv_connector='MoRIIOConnector', kv_role='kv_producer', ...)
}

Initializing a V1 LLM engine (v0.1.dev0) with:
  dtype=torch.bfloat16, tensor_parallel_size=16, quantization=fp8,
  kv_cache_dtype=fp8_e4m3, enable_chunked_prefill=True,
  speculative_config=SpeculativeConfig(method='mtp', num_spec_tokens=1),
  attention_backend(decode)=ROCM_AITER_MLA,
  attention_backend(prefill)=FLASH_ATTN MLA,
  moe_backend=AITER Fp8 MoE

Workload driver

gsm8k via lm_eval (1319 prompts, num_concurrent=30,
max_tokens=12288, temperature=0), pointed at the proxy on the
prefill head.

Pre-fix observation

results/exp34-tp16-sym-1p1d-cycle12/, 2026-05-15 08:53 UTC, same
hardware and launch as above except this PR and #43063 are not
applied. gsm8k progresses to 141 / 1319 prompts, then EngineCore
crashes:

ValueError: Cannot parse peer zmq_address from request_id: '<16-hex-id>'
  at moriio_common.add_new_req

(The prefill engine hits the aborted before scheduling branch — the
external prefix cache returned a hit and reclaimed the slot before the
scheduler dispatched it. The 16-hex internal request_id has no
___prefill_addr_..._UUID prefix to parse.)

Post-fix observation

results/exp34-tp16-sym-1p1d-cycle3-v2/, 2026-05-15 11:50 UTC, with
this PR and #43063 both applied. gsm8k completes 1319 / 1319 in
one run:

"results": {
  "gsm8k": {
    "exact_match,strict-match": 0.9492039423805914,
    "exact_match_stderr,strict-match": 0.006048352096878092,
    "exact_match,flexible-extract": 0.9476876421531463,
    "exact_match_stderr,flexible-extract": 0.006133057708959227
  }
}

No ValueError from add_new_req — the cleanup-path short-id requests
take the fallback branch and return cleanly.

In-tree unit tests

pytest tests/v1/kv_connector/unit/test_moriio_connector.py -v
# ✓ test_write_mode_saves_local_block_ids
# ✓ test_write_mode_with_chunked_prefill_saves_local_block_ids
# ✓ test_read_mode_loads_remote_block_ids
# ✓ test_register_kv_caches
# ✓ test_moriio_handshake_returns_metadata

All five pass (no regression). The existing tests don't construct
short-id / missing-kv_transfer_params inputs to exercise the new
fallback branch; that path is only exercised by the end-to-end
cluster run above. Happy to add a targeted unit test if reviewers
want.

Lint

pre-commit run --files \
  vllm/distributed/kv_transfer/kv_connector/v1/moriio/moriio_common.py
pre-commit run mypy-3.10 --files \
  vllm/distributed/kv_transfer/kv_connector/v1/moriio/moriio_common.py \
  --hook-stage manual
# All hooks: Passed.

Gemini-code-assist review response

Both items raised in the automated review are addressed in the current
commit (see "Changes" above):

1. remote_hosts list-vs-string handling — explicit
   isinstance(remote_hosts_raw, str) branch + list() conversion
   otherwise; empty list re-raises.
2. .get() on optional keys — remote_block_ids and
   remote_engine_id now use .get() with safe defaults so that
   cleanup-path requests (the same code path this PR exists to
   protect) don't crash on the next [] access.

AI assistance disclosure

This PR was drafted with AI assistance (Claude Code). The diff is 1
file, ~40 lines, isolated to the parse-fallback path. I
(chaemin.lim@mangoboost.io) have reviewed and defend each changed
line; the fallback values (DEFAULT_HANDSHAKE_PORT,
DEFAULT_NOTIFY_PORT, remote_hosts[0]) are the same constants the
runner harness already configures on every MoRIIO container, so the
fallback is provably consistent with the deployment-time config rather
than a guess.

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[gemini-code-assist]

Code Review

This pull request updates the add_new_req function in moriio_common.py to provide a fallback mechanism for resolving peer host and port information when the request_id cannot be parsed, which typically occurs during cleanup-path requests. The reviewer identified two critical robustness issues: first, the fallback logic for remote_host should explicitly check if remote_hosts is a list or a string to prevent incorrect IP address extraction; second, subsequent accesses to kv_transfer_params for block and engine IDs should use .get() to avoid KeyError crashes in scenarios where these parameters are absent.

[gemini-code-assist]

If kv_transfer_params.get("remote_hosts") returns a string instead of a list (which can happen depending on the upstream proxy's serialization or configuration), remote_hosts[0] will only extract the first character of the IP address string. This will lead to a connection failure that is difficult to diagnose. It is safer to handle both types explicitly.

Suggested change

	remote_host = remote_hosts[0]
	remote_host = remote_hosts[0] if isinstance(remote_hosts, list) else remote_hosts

[gemini-code-assist]

For requests that are aborted before scheduling (handled in request_finished lines 567-576), kv_transfer_params may not contain remote_block_ids or remote_engine_id. Accessing them with [] in the subsequent lines (381-382) will cause a KeyError, leading to the same EngineCore crash this PR aims to fix. Consider using .get() with appropriate defaults (e.g., [] for block IDs and "" for engine ID) to ensure robustness in the cleanup path.