The Phantom Running State: Debugging a Tunnel Failure in a Distributed Proving System

In distributed systems, the most insidious bugs are often those where the system appears to be working correctly while silently failing beneath the surface. Message 1417 of this opencode session captures exactly such a moment: a newly deployed GPU proving instance reports itself as "running" on the vast-manager dashboard, yet its core workload — the Curio daemon — is crashing every five seconds, unable to reach the Lotus blockchain node it depends on. The assistant's investigation and response in this single message reveals a masterclass in operational debugging: tracing a symptom (a "running" state) back through multiple layers of abstraction (a supervisor loop, a tunnel client, a port mismatch, a Docker entrypoint) to its root cause, and then making a pragmatic decision about how to remediate both the immediate instance and the fleet of future deployments.

The Message

Here is the message in full (with secrets redacted):

I see — curio exits immediately because it can't connect to the chain node. Then the supervisor loop restarts it every 5 seconds. It signals running on the first start (line 319-324), which is why the state is running. But curio keeps crashing and restarting because port 1234 isn't tunneled.

The fix is already in the entrypoint (added -L 1234). Now I need to: 1. Rebuild and push the Docker image 2. The running instances can be fixed by SSH'ing in and restarting portavailc with the correct ports

Let me first fix the running instances by restarting their portavailc with -L 1234 added. Actually, it'd be simpler to just kill and redeploy them after pushing the new image. But the Docker build takes a while. Let me fix the one running instance manually first, then rebuild:

`` [bash] ssh -p 41071 root@141.0.85.200 'ps aux | grep portavailc | grep -v grep' 2>&1 || echo "SSH failed" root 325 0.0 0.0 1821236 6160 ? Sl 09:56 0:00 portavailc --server 45.33.141.226:22222 --secret [REDACTED] -L 1235 -L 5433 -L 9042 ``

The Context: A Chain of Dependencies

To understand why this message matters, one must appreciate the architecture at play. The system being built is a distributed proving network for Filecoin's Curio protocol. Each worker instance runs inside a Docker container on a rented GPU machine from Vast.ai. Inside that container, a supervisor script (entrypoint.sh) orchestrates a multi-stage startup:

Portavailc tunnel: A secure TCP tunnel is established back to a central controller, forwarding specific ports from the worker to the controller.
Parameter fetching: Cryptographic proving parameters are downloaded.
Benchmarking: The GPU's proving performance is measured.
Supervisor loop: Two daemons are started — cuzk-daemon (the proving engine) and curio (the chain-facing daemon that coordinates proving tasks). Curio, in particular, needs to connect to a Lotus Filecoin node via WebSocket at ws://127.0.0.1:1234/rpc/v1. This Lotus node does not run on the worker itself; it runs on the controller. The connection is made possible by the portavailc tunnel, which forwards port 1234 from the controller to the worker's localhost. The bug was introduced when the entrypoint script was written: the portavailc command included -L 1235 -L 5433 -L 9042 but omitted -L 1234. Without port 1234 forwarded, Curio cannot reach the Lotus node, fails to connect, and exits with an error.## The "Running" Mirage: How a Supervisor Loop Masks Failure The key insight in this message — and the reason the bug was non-obvious — is the interaction between the supervisor loop and the state-reporting mechanism. The assistant explains this clearly: "It signals running on the first start (line 319-324), which is why the state is running. But curio keeps crashing and restarting because port 1234 isn't tunneled." Let's unpack what this means. The entrypoint script's supervisor loop (visible in the surrounding context at lines 300-330) works as follows:
Start cuzk-daemon in the background.
Wait for it to become ready (polling its health endpoint).
Once cuzk is ready, start curio in the background.
Immediately signal to the vast-manager that the instance is "running" — this is the state transition that updates the dashboard.
Then enter a monitoring loop that checks both daemons periodically. The problem is that step 4 happens before Curio has had a chance to fail. Curio starts, attempts to connect to Lotus, fails immediately (because port 1234 is not tunneled), and exits. The supervisor loop detects this, logs the failure, and restarts Curio after a 5-second delay. But the "running" state has already been reported and persists. The vast-manager sees state=running and considers the instance healthy, while in reality Curio is crash-looping every few seconds. This is a classic failure of state semantics: the system uses a state machine where "running" means "startup sequence completed and daemons launched," not "daemons are healthy and doing useful work." The assistant correctly identifies this gap in reasoning, noting that the state is set on "the first start" — before any validation of the daemon's actual health.

The Reasoning Process: From Symptom to Root Cause

The assistant's reasoning in this message is worth examining step by step, as it reveals a disciplined approach to operational debugging.

Step 1 — Connect the symptom to the error. The user reported that Curio failed to start with a "connection refused" error on port 1234. The assistant immediately recognizes this as a tunnel issue, not a Curio bug. The error message is specific: "cannot dial address ws://127.0.0.1:1234/rpc/v1 for dial tcp 127.0.0.1:1234: connect: connection refused." This means nothing is listening on port 1234 inside the container — Lotus is on the other side of the tunnel, and the tunnel isn't forwarding that port.

Step 2 — Check the tunnel infrastructure. The assistant first verifies that the controller-side daemon (portavaild) is running and configured to forward port 1234. It is. Then checks that Lotus itself is listening on port 1234 on the controller. It is. The problem must be on the client side — the portavailc tunnel process running inside the container.

Step 3 — Read the entrypoint to find the bug. By grepping for "portavailc" and reading the relevant section of entrypoint.sh, the assistant finds the exact line where the tunnel is started. The command includes -L 1235 -L 5433 -L 9042 but omits -L 1234. This is the root cause: a simple omission in a port-forwarding command.

Step 4 — Understand the state mismatch. Having found the fix (adding -L 1234), the assistant then considers the operational impact. The dashboard shows the instance as "running," but Curio is failing. By reading the supervisor loop code, the assistant deduces that "running" is set on the first launch attempt, before Curio has a chance to fail. This explains why the dashboard is misleading.

Step 5 — Plan the remediation. The assistant considers two approaches: (a) fix the running instance in-place by SSH'ing in and restarting portavailc with the correct flags, or (b) rebuild the Docker image and redeploy. Option (a) is faster for the immediate instance; option (b) is necessary for all future instances. The assistant decides to do both, starting with the manual fix because "the Docker build takes a while."

Assumptions and Their Validity

Every debugging session rests on assumptions, and this message reveals several that are worth examining.

Assumption 1: The supervisor loop's state reporting is correct. The assistant initially assumed that "running" meant the instance was healthy. It was only by reading the code that the assistant discovered the state is set optimistically on first launch, not after health verification. This assumption was reasonable — most systems report "running" only after confirming the service is up — but it was wrong for this particular codebase.

Assumption 2: The portavailc tunnel is the only path for port 1234. The assistant correctly assumes that the Lotus API must be reached through the tunnel. There is no alternative route (e.g., direct public IP access) because the Lotus node is on the controller's localhost. This assumption is validated by the architecture: the controller exposes port 1234 only via the portavaild tunnel service, not publicly.

Assumption 3: SSH access to the worker instance will work. The assistant attempts to SSH into the running instance (141.0.85.200 on port 41071) to fix the tunnel in-place. This assumes that the instance is SSH-accessible from the controller, which requires that the Vast.ai instance has SSH enabled and the controller has the SSH key. The command succeeds, validating this assumption.

Assumption 4: The fix is purely additive. Adding -L 1234 to the portavailc command is safe because it only adds a new forwarding rule; it doesn't change existing behavior. The assistant does not consider whether adding this port might conflict with anything else, which is a reasonable judgment given that port 1234 is not used by any other service inside the container.## Input Knowledge Required to Understand This Message

To fully grasp what the assistant is doing in message 1417, a reader needs several layers of context:

Architectural knowledge: One must understand that the proving system has a controller-worker topology, where the controller runs a Lotus Filecoin node and a portavaild tunnel server, while workers run cuzk-daemon and curio inside Docker containers. The tunnel is the sole communication channel between them.

Vast.ai operational knowledge: Workers are rented GPU instances from Vast.ai, provisioned with an --onstart-cmd that pulls and runs a Docker image. The vast-manager tracks these instances through a state machine (registered → params_done → benching → bench_done → running → killed) and periodically monitors their health.

Portavail tooling knowledge: Portavail is a custom TCP tunnel tool. The daemon (portavaild) runs on the controller and listens for incoming tunnel connections. The client (portavailc) runs on each worker and establishes outbound tunnels using -L flags to specify which local ports to forward.

Shell scripting patterns: The supervisor loop in entrypoint.sh uses a while true loop with background process management, PID tracking, and health checks. Understanding how &, wait, and kill interact is essential to see why the "running" state is set prematurely.

Go and SQLite knowledge: The vast-manager is written in Go and uses SQLite for persistence. The dashboard handler queries both the vast cache (in-memory, from Vast.ai's API) and the database (for killed instances) to build its response.

Without this input knowledge, the assistant's actions might seem arbitrary or overly specific. With it, the reasoning becomes transparent and even elegant.

Output Knowledge Created by This Message

This message produces several valuable outputs that advance the debugging effort:

A confirmed root cause: The assistant establishes definitively that the missing -L 1234 flag is the reason Curio cannot connect to Lotus. This is not speculation — it is confirmed by reading the entrypoint code and observing the portavailc command line on the running instance.

A documented state-machine bug: The assistant identifies that the "running" state is misleading because it is set before Curio's health is verified. This is a design flaw in the supervisor loop that could cause future confusion if not addressed.

A prioritized remediation plan: The assistant produces a two-track plan: (1) fix the immediate instance by SSH'ing in and restarting portavailc with the correct flags, and (2) rebuild the Docker image so all future instances are born with the fix. The assistant explicitly acknowledges the tradeoff — Docker build time vs. manual fix speed — and chooses the pragmatic path.

A verified SSH connection: The bash command at the end of the message confirms that the worker instance is accessible and that the portavailc process is indeed missing the -L 1234 flag. This is empirical evidence that closes the loop between hypothesis and observation.

Mistakes and Incorrect Assumptions

While the assistant's reasoning is largely sound, there are a few points worth examining critically.

The assumption that fixing the running instance manually is worthwhile. The assistant says "Let me fix the one running instance manually first, then rebuild." But the SSH output reveals that the instance in question (141.0.85.200) is running portavailc without -L 1234. Even if the assistant fixes this instance by killing and restarting portavailc with the correct flags, the fix will only last until the container restarts — because the entrypoint script (which hasn't been updated yet) will re-create the tunnel without -L 1234. The manual fix is temporary unless the Docker image is also rebuilt. The assistant acknowledges this implicitly by planning to rebuild, but doesn't explicitly note the ephemeral nature of the SSH fix.

The assumption that only one instance is affected. The dashboard output in message 1414 shows multiple active instances, including several in params_done state. All of these instances were deployed with the same Docker image, so all of them lack the -L 1234 tunnel. The assistant focuses on the one "running" instance, but the others will hit the same Curio failure when they transition to the supervisor loop. A more complete plan might involve fixing all accessible instances or at least acknowledging the fleet-wide scope of the bug.

The assumption that the fix is complete. Adding -L 1234 to the portavailc command ensures the tunnel exists, but it does not guarantee that Curio will connect successfully. There could be additional issues — authentication mismatches, WebSocket protocol errors, or routing problems — that only surface after the tunnel is fixed. The assistant is appropriately cautious, planning to verify after the fix, but the message itself treats the tunnel as the sole root cause.

The Thinking Process: A Window into Operational Debugging

What makes this message particularly valuable as a case study is the visible thinking process. The assistant does not just state the fix; it walks through the reasoning chain that led there. This is visible in the structure of the message itself:

Observation: "curio exits immediately because it can't connect to the chain node."
Deduction: "Then the supervisor loop restarts it every 5 seconds."
Insight about the state bug: "It signals running on the first start (line 319-324), which is why the state is running."
Root cause: "But curio keeps crashing and restarting because port 1234 isn't tunneled."
Fix status: "The fix is already in the entrypoint (added -L 1234)."
Plan: "Now I need to: 1. Rebuild and push the Docker image 2. The running instances can be fixed by SSH'ing in and restarting portavailc with the correct ports"
Tradeoff analysis: "Actually, it'd be simpler to just kill and redeploy them after pushing the new image. But the Docker build takes a while. Let me fix the one running instance manually first, then rebuild."
Verification: The SSH command to confirm the hypothesis. This is textbook systematic debugging: observe the symptom, trace it to the mechanism, identify the root cause, verify the hypothesis, plan the fix, and execute. The assistant even considers the tradeoff between two remediation strategies and makes a pragmatic choice based on time constraints.

Conclusion

Message 1417 is a small but perfectly formed example of operational debugging in a complex distributed system. It demonstrates how a single missing flag in a tunnel command can produce a cascade of misleading signals — a "running" state that masks a crash-looping daemon, a dashboard that reports health where there is none, and a user who sees green lights while the system silently fails. The assistant's disciplined reasoning, from symptom to root cause to remediation plan, shows the value of understanding the full architecture rather than treating symptoms in isolation. And the message itself, with its clear thinking and pragmatic decision-making, serves as a template for how to approach similar failures in any distributed system.