Doca Socket Relay

DOCA Socket Relay

Examples

• "Can I move my socket app onto BlueField without rewriting it?" — this is in scope. Pick deployment shape first; do not port the app onto comch here.

• "The relay is up but the host app gets ECONNREFUSED." — walk bind / listen before assuming the DPU peer is down.

Quick facts

The authoritative source for the binary name, flags and paths is the public DOCA Socket Relay guide for your release; confirm them with the installed tool's --help before quoting any of them. As that guide describes it:

• One relay instance per AF_UNIX server application; SOCK_STREAM only; at most 512 client connections.

• The BlueField instance takes a socket path, a Comch service name, the device PCI address and the representor PCI address, and connects to your AF_UNIX server; the host instance takes the same without the representor and binds the socket path your clients connect to. Both sides use the same Comch name.

• ECONNREFUSED on the socket path: nothing is listening there: the host relay is not running, its socket path differs from the one the client uses, or a stale socket file is left over. Then check the BlueField instance is up and both Comch names match; raise the log level (see --help).

• Only the host-side application may terminate connections.

Instructions

Follow Loading order below. Open the tasks companion for configure / run / debug. Open the capabilities companion for what the relay carries. Do not open every companion file.

Where to start: This is a tool skill for invoking the DOCA Socket Relay — the host ↔ BlueField bridge that lets a socket-oriented host application terminate its sockets locally while the relay forwards the traffic to a DPU-side terminator across the DOCA fabric. Open the tasks companion and start at ## configure for the deployment-shape × socket-type × forwarding-endpoint decision, then ## run for the bind → connect → round-trip flow. Open the capabilities companion when the question is what state can the relay carry, what does it report, and what does its data-path posture imply. If the user has not installed DOCA yet, route to doca-setup/SKILL.md first. If the user is asking about the host ↔ DPU control plane rather than the data plane the relay carries, route to doca-comch/SKILL.md — the relay is the data-plane counterpart to comch.

How to use this skill. Read this file, then search the companion file for the ## <name> heading the question needs and read that whole section. Answer completely from it, quoting only its symbols and commands. Do not browse docs; use the entry points in doca-public-knowledge-map. Give environment checks as commands for the user's DOCA host. For out-of-scope requests, name the skill that owns them and stop.

Example questions this skill answers well

The CLASSES of socket-relay questions this skill is built to answer, each with one worked example. The class is the load-bearing piece; the worked example is one instance.

• "Can I move my existing socket-based application onto a DOCA fabric without rewriting it?" — worked example: "a host service speaks a socket protocol to a peer; I want the peer to live on the BlueField DPU instead, but I do not want to port the application to the comch programming surface". Answered by the use-case framing in the capabilities companion

  • the deployment-shape decision in the tasks companion.

• "Where does the relay sit, and what runs on the host vs the DPU?" — worked example: "do I run one relay process on the host, a sidecar next to my app, or a relay container on the BlueField — and what is on the DPU side that actually terminates the connection?". Answered by the three-axis configuration model (deployment shape × socket type × forwarding endpoint) in the capabilities companion

  • the tasks companion step 2.

• "My relay is up but the host application cannot connect." — worked example: "the relay process is running but the host app reports ECONNREFUSED / connect timeout when it tries the socket / port the relay should be listening on". Answered by the layered error taxonomy in the capabilities companion layers 1-3 + the bind / accept ladder in the tasks companion.

• "Bytes leave the host but never arrive on the DPU side." — worked example: "the host app's socket connect succeeded, the relay reports the connection accepted, but the DPU-side terminator never sees the data". Answered by the forwarding-endpoint layer in the capabilities companion layer 4 + the silent-data-path failure mode named in the capabilities companion.

• "How do I prove the relay is the right answer before I admit the whole fleet onto it?" — worked example: "I have N host clients; I want to confirm one of them works end-to-end before pointing the rest at the relay". Answered by the smoke-before-bulk loop in the tasks companion (bind → confirm one host app connects → confirm one round-trip end-to-end → only then admit the fleet).

• "Is this Socket Relay shipped on my installed DOCA, and does its version match the comch / eth pieces it sits on?" — worked example: "is the relay binary present on this host, and does it agree with pkg-config --modversion doca-common". Answered by the version overlay in the capabilities companion, which redirects to the canonical doca-version/SKILL.md rules and adds the Socket Relay specifics (presence check, host vs BlueField packaging, agreement with companion libraries).

When to load this skill

Load this skill when the user is — or the agent needs to — drive the DOCA Socket Relay on a real host or BlueField Arm with DOCA installed (or inside the public NGC DOCA container with the right device passthrough). Concretely:

• Migrating a socket-based application off a same-host peer onto a BlueField-side terminator without rewriting the application.

• Picking the relay's deployment shape (in-process beside the app, sidecar process / container, or a service container on the BlueField) for a specific environment.

• Configuring the host-side socket the relay binds and the DPU-side forwarding endpoint the relay points at, before any application client tries to connect.

• Walking the bind → connect → round-trip → admit-fleet loop on a brand-new relay deployment.

• Diagnosing a "host app cannot connect", "connection accepted but no bytes flow", or "first round-trip works, the rest hang" symptom against the relay's layered error surface.

• Cross-checking the relay's view against the host application side and the DPU-side terminator when the three appear to disagree.

Do not load this skill for general DOCA orientation, the comch programming API, RDMA programming, line-rate raw packet I/O, or DOCA install. For those, route to doca-public-knowledge-map/SKILL.md, doca-comch/SKILL.md, doca-eth/SKILL.md, or doca-setup/SKILL.md.

What this skill provides

This is a thin loader. Substantive material lives in two companion files:

• the capabilities companion — what the Socket Relay carries and changes: the three-axis configuration model (deployment shape × socket type / protocol × forwarding endpoint), the read-only vs state-changing operation split, the version-availability overlay that redirects to doca-version/SKILL.md, the layered error taxonomy (tool-not-installed / relay-not-bound / host-app-not-connecting / DPU-side-terminator-not-reachable / permission / version / cross-cutting), the relay's role as the data-plane counterpart to doca-comch/SKILL.md, and the high-stakes safety policy that makes a misconfigured forwarding endpoint a silent data-path break.

• the tasks companion — step-by-step workflows for the in-scope task verbs: configure (the three-axis decision + the precondition probe), build (route to install — the relay is shipped pre-built), modify (refuse — modify the invocation / deployment, not the binary), run (the bind → connect → round-trip flow), test (the smoke-before-bulk eval loop), debug (the layered diagnosis ladder), plus a Deferred task verbs block and a Command appendix that honors the bundle's doca-structured-tools-contract/SKILL.md preamble.

The skill assumes a host or BlueField where DOCA is already installed (or the public NGC DOCA container is running with the right device passthrough) and the operator has whatever privileges the public DOCA Socket Relay guide requires for the chosen deployment shape.

What this skill deliberately does not ship

This skill is agent guidance, not a samples or scripts bundle. To keep the boundary clean, it deliberately does not contain — and pull requests should not add:

• Verbatim binary names, flag inventories, subcommand names, socket-path defaults, port numbers, or output column names. The public DOCA Socket Relay guide on docs.nvidia.com and the installed --help on the user's version are the joint source of truth; copying them here pins the skill to one release and silently rots when the relay evolves. The skill routes the agent at those sources instead.

• Pre-baked example output. Output is install-, version-, and deployment-specific. A captured example will mislead an operator on a different platform / state.

• Wrappers, parsers, or scripts in any language that consume the relay's output. The output format is documented; users who want to script against it should read the live guide and write the parser against their installed version.

• A samples/ or reference/ subtree. This is a thin loader for a documented DOCA artifact; substantive material lives on the public page and in --help.

Loading order

1. Read this skill first to confirm the user's question is in scope (the user wants to bridge a socket-based application onto the DPU without rewriting it onto the DOCA programming surface, not learn the comch / eth / RDMA APIs).

2. For what the relay carries, the three-axis configuration model, the read-only vs state-changing split, version availability, the layered error surface, observability, and safety posture, see the capabilities companion.

3. For the documented invocations and the smoke-before-bulk workflow — configure, build, modify, run, test, debug, plus the Command appendix — see the tasks companion.

Related skills

• doca-comch/SKILL.md — the host ↔ DPU control-plane primitive (PCIe-based message channel between a host and a DPU process). The Socket Relay is the data-plane counterpart for socket-oriented applications: comch is what an application uses to coordinate across the host ↔ DPU boundary programmatically; the relay is what an application uses to carry socket-shaped bytes across that boundary without being rewritten. Pair the two when an application owner is migrating in stages — control plane first via comch, data plane via the relay until a per-library rewrite is justified.

• doca-eth/SKILL.md — the line-rate raw packet I/O surface that sits below the socket level. The relay presents a socket-shaped interface to the application and rides the underlying DOCA fabric; doca-eth is the right answer when the application can be rewritten to operate on packets directly rather than sockets, and when the throughput / latency profile the relay achieves is no longer sufficient.

• doca-container-deployment/SKILL.md — the BlueField service-runtime contract (kubelet standalone + static-pod manifests + per-service config-file mount). Load this alongside the present skill when the operator's chosen deployment shape is a relay container running on the BlueField rather than a host-side process; the runtime contract there owns the pod-spec / image-pull / static-pod / liveness pieces, this skill owns the relay-specific config.

• doca-comm-channel-admin/SKILL.md — the operator-side admin CLI for comch channels. The list → inspect → decide pattern there is the same shape the Socket Relay uses for its own state: read-only inspection first, state-changing operations gated on a clean smoke. Both tools are members of the same family and the same patterns apply.

• doca-public-knowledge-map/SKILL.md — routing to the public DOCA Socket Relay guide and the rest of the public DOCA documentation set. The canonical URL is reached via doca-public-knowledge-map ## DOCA tools (doca-public-knowledge-map/SKILL.md#doca-tools).

• doca-version/SKILL.md — canonical DOCA version-handling rules. The ## Version compatibility section in the capabilities companion is a concise overlay that redirects here for the body.

• doca-structured-tools-contract/SKILL.md — the bundle's detect → prefer → fall back → report contract for structured helper tools. The Command appendix in the tasks companion honors this contract.

• doca-setup/SKILL.md — env preparation, install verification, representor visibility checks, and the I have no install yet path with the public NGC DOCA container. This skill assumes its preconditions are satisfied.

• doca-debug/SKILL.md — the cross-cutting debug ladder. The Socket Relay slots in at the runtime layer as a data-path bridge whose layered error surface escalates to the cross-cutting ladder when the cause is below DOCA.