The Moment the OOM Killer Struck: A Pivotal Monitoring Checkpoint in CuZK Deployment on Vast.ai

In any complex distributed systems deployment, there comes a moment when a carefully laid plan meets the messy reality of heterogeneous hardware. Message 1024 of this opencode session captures precisely such a moment: a routine monitoring check that transforms from a confirmation of progress into a diagnostic crisis. The assistant, having just created two new Vast.ai GPU instances with a freshly rebuilt Docker image, checks their status after a ten-minute wait and discovers that one of them has been silently killed by the operating system's out-of-memory (OOM) killer. This single message represents the inflection point where the deployment effort pivots from platform-specific debugging to hardware-aware resource tuning, and it reveals critical assumptions about memory requirements that had gone unexamined until this moment.

The Message in Full

The message reads as follows (with IP addresses and internal details preserved as they appear in the conversation):

[assistant] BC instance is finishing up (empty-sector-update params downloaded). Norway instance is at 82% of the 44GB file with a slow download error (aria2 auto-retries). Let me wait another 10 minutes.

[bash] sleep 600 && echo "=== Manager State ===" && ssh 10.1.2.104 "curl -s http://127.0.0.1:1235/api/dashboard | jq '.instances[] | {label, state, bench_rate, log_lines}'" && echo "=== Instance 32711932 (BC) ===" && ssh -p 48237 root@70.69.192.6 "tail -10 /var/log/entrypoint.log" 2>&1 && echo "=== Instance 32711934 (NO) ===" && ssh -p 41122 root@141.195.21.87 "tail -10 /var/log/entrypoint.log" 2>&1

=== Manager State === { "label": "C.32711934", "state": "params_done", "bench_rate": null, "log_lines": 3987 } { "label": "C.32711932", "state": "killed", "bench_rate": 0, "log_lines": 4013 } === Instance 32711932 (BC) === Welcome to vast.ai. If authentication fails, try again after a few seconds, and double check your ssh key. Have fun! (OK):download completed. 2026-03-12T01:38:41.036Z INFO paramfetch fastparamfetch/paramfetch.go:227 Parameter file /var/tmp/filecoin-proof-parame...

The structure is deceptively simple: a commentary line from the assistant expressing an optimistic assessment, a compound bash command that polls both instances, and the raw output revealing the truth. The contrast between the assistant's expectation ("BC instance is finishing up") and the reality ("state: killed") is the dramatic core of this message.

Why This Message Was Written: The Motivation and Context

This message was written as part of a non-interactive deployment session. The user had instructed the assistant to work with two specific Vast.ai hosts (93197 and 88910), destroy old instances, create new ones with a fixed Docker image, and ensure they run correctly — all without stopping or asking questions. The assistant was in the middle of a multi-hour automated deployment campaign.

The immediate context is critical. In the preceding messages (1018–1023), the assistant had:

Created two new instances: 32711932 on host 93197 (BC Canada, 2x RTX 3090, 125GB RAM) and 32711934 on host 88910 (Norway, 1x RTX 4090, 500GB RAM)
Confirmed both were running and had started their entrypoint scripts
Watched them begin downloading Filecoin proof parameters — massive files ranging from 44 to 56 GB each
Performed two prior monitoring checks (messages 1022 and 1023) where both instances were still in the parameter download phase Message 1024 is the third monitoring checkpoint. The assistant had waited 10 minutes (sleep 600) between checks, and the purpose was to verify that parameter downloads had completed and that the benchmark phase had begun. The assistant's commentary reveals their mental model: they believed the BC instance had finished its downloads (the last file being "empty-sector-update params") and the Norway instance was at 82% of a 44GB file with a minor download speed issue that aria2 would handle via auto-retries. The motivation for writing this message was to gather status data — to confirm that the deployment was proceeding as expected. It was a verification step in a long chain of automated operations. The assistant had no reason to expect failure; the Docker image had been rebuilt with fixes for earlier issues (the VAST_CONTAINERLABEL problem, the benchmark script hardening, the monitor matching logic), and both instances had started cleanly.

Assumptions Embedded in the Message

The message reveals several assumptions, some explicit and some implicit:

Assumption 1: Parameter download completion implies readiness. The assistant assumed that once the BC instance finished downloading parameters, it would proceed smoothly to the benchmark phase. The "empty-sector-update params downloaded" status was taken as a positive signal. In reality, the transition from parameter download to benchmark execution is precisely when memory pressure spikes, because the CuZK proving engine begins synthesizing proof partitions with organic (uncached) memory allocation.

Assumption 2: The Norway instance's slow download was a non-issue. The assistant noted "a slow download error (aria2 auto-retries)" but dismissed it as a transient network issue that the download tool would handle. This was correct — the Norway instance did eventually complete its downloads — but it reflects an assumption that network-level problems are the primary failure mode at this stage, not resource exhaustion.

Assumption 3: 125GB RAM is sufficient for the default configuration. This is the most consequential assumption. The assistant had configured the entrypoint script to use partition-workers=10 for instances with less than 400GB RAM (as seen in earlier messages). The BC Canada instance had 125GB RAM, which triggered this configuration. The assumption was that 125GB would be adequate for 10 simultaneous partition syntheses during the first (uncached) proof run. This assumption proved catastrophically wrong.

Assumption 4: The "killed" state would be visible and interpretable. The assistant designed the monitoring system to surface instance states through the vast-manager dashboard API. The state: killed and bench_rate: 0 fields provided clear signals that something had gone wrong. However, the assistant did not yet know why it was killed — that diagnosis would require deeper investigation in the subsequent messages (1025–1026).

Input Knowledge Required to Understand This Message

To fully grasp what is happening in message 1024, one needs knowledge spanning several domains:

Vast.ai platform knowledge: Understanding that Vast.ai is a decentralized GPU rental marketplace, that instances are Docker containers running on remote hosts, that the --onstart-cmd workaround is needed because --ssh mode replaces the Docker ENTRYPOINT, and that instance states like "running" and "killed" reflect the container's lifecycle as reported by the platform.

The CuZK proving system: Knowledge that Filecoin proof generation involves downloading large parameter files (44–56 GB each), that the first proof requires "PCE extraction" (pre-compiled constraint evaluator) which allocates memory organically during synthesis, and that subsequent proofs use cached PCE data with pre-allocated buffers requiring less memory. The term "partition-workers" refers to the number of parallel synthesis threads, each of which grows its memory footprint during the first run.

The deployment architecture: Understanding that the assistant has set up a management service (vast-manager) on a controller host (10.1.2.104) that tracks instance states in a SQLite database and provides a dashboard API. The instances register themselves, download parameters, run benchmarks, and report results back to the manager.

The bash command structure: The compound command chains four operations: (1) query the manager dashboard for all instance states, (2) SSH into the BC instance to check its entrypoint log, (3) SSH into the Norway instance to check its entrypoint log. The sleep 600 at the start indicates a deliberate 10-minute wait between monitoring cycles.

Output Knowledge Created by This Message

This message produces several critical pieces of knowledge that reshape the deployment strategy:

Knowledge 1: The BC Canada instance (32711932) has been killed. This is the primary output. The instance that was running and downloading parameters is now dead. The bench_rate: 0 field confirms it never completed a benchmark. The log_lines: 4013 indicates it was actively logging right up until the kill — it didn't crash silently.

Knowledge 2: The Norway instance (32711934) has completed parameter downloads. The state: params_done indicates success at this phase. The bench_rate: null means the benchmark hasn't started or hasn't completed yet. This instance is on track.

Knowledge 3: The BC instance's last log entry shows a completed parameter download. The SSH output shows (OK):download completed for what appears to be the last parameter file, timestamped at 01:38:41. This narrows the window of failure — the instance died shortly after completing downloads, likely during the transition to the benchmark phase.

Knowledge 4: A differential diagnosis is required. The two instances have different hardware configurations (2x RTX 3090 with 125GB RAM vs. 1x RTX 4090 with 500GB RAM) and are at different stages (BC finished downloads and died; Norway is still downloading). This creates a natural experiment: if the Norway instance succeeds with 500GB RAM but the BC instance failed with 125GB RAM, the likely culprit is memory exhaustion.

The Thinking Process Visible in the Message

The assistant's reasoning is visible in the commentary line that precedes the bash command. The phrase "BC instance is finishing up (empty-sector-update params downloaded)" reveals the assistant's interpretation of the previous monitoring data. In message 1023, the BC instance was still downloading large .params files. By message 1024, the assistant believes those downloads are nearly complete, with only the "empty-sector-update" file remaining.

The phrase "Norway instance is at 82% of the 44GB file with a slow download error (aria2 auto-retries)" shows the assistant tracking progress at a granular level — they know which specific file is being downloaded and what percentage is complete. The mention of "aria2 auto-retries" indicates familiarity with the download tool's behavior and a judgment that this is not a critical failure.

The concluding statement "Let me wait another 10 minutes" reveals the assistant's decision-making process: they are in a monitoring loop, waiting for both instances to reach the benchmark phase. The 10-minute interval is a heuristic choice — long enough for meaningful progress but short enough to catch failures quickly.

What is not visible in this message but becomes clear in retrospect is the assistant's lack of awareness about the OOM risk. The assistant does not express concern about memory constraints. The commentary is optimistic, even casual. This is not negligence — the assistant had no prior evidence that 125GB RAM would be insufficient. The earlier deployment on a 251GB RAM instance (32710471) had run successfully, and the partition-workers calculation was based on a simple RAM threshold (<400GB → 10 workers). The failure mode — organic memory allocation during uncached PCE synthesis exceeding available RAM — was not yet in the assistant's mental model.

Mistakes and Incorrect Assumptions

The most significant mistake in this message is not in the message itself but in the assumptions that led to it. The assistant assumed that the BC instance was "finishing up" successfully when in fact it was about to be killed. This is not a mistake in the monitoring logic — the assistant correctly queried the state — but rather an over-optimistic interpretation of the available signals.

A subtler issue is the monitoring interval. The assistant waited 10 minutes between checks. The BC instance's last log entry was at 01:38:41, and the check in message 1024 occurred approximately 10 minutes later. The instance was likely killed shortly after 01:38:41, meaning the assistant discovered the failure within 10 minutes of its occurrence. This is reasonable, but a shorter interval might have captured the exact moment of failure and provided more diagnostic information (e.g., OOM killer messages in the kernel log before the container was fully destroyed).

The assistant also did not include memory usage data in the monitoring command. The query only captured instance state, benchmark rate, and log lines. Adding free -h or dmesg | grep -i oom to the SSH commands could have immediately confirmed the OOM hypothesis. This diagnostic gap is filled in the subsequent messages (1025–1026), where the assistant reads the full benchmark log and discovers the daemon was killed.

How Decisions Were Made

The decision to check both instances simultaneously with a single compound command reflects the assistant's prioritization of efficiency. Rather than checking each instance sequentially with separate commands, the assistant chains them together, collecting all data in one round trip. This is consistent with the non-interactive, automated nature of the deployment session — the assistant is operating under a directive to work without stopping or asking questions.

The decision to wait 10 minutes between checks is a calibration between responsiveness and patience. Parameter downloads take 10–20 minutes for the large files, so checking every 10 minutes provides a reasonable update cadence without overwhelming the instances with SSH connections.

The decision to query the manager dashboard first, then SSH into each instance, establishes a hierarchy of information: the dashboard provides the synthesized state (params_done, killed, etc.), while the SSH logs provide the raw detail. This is sound diagnostic practice — start with the summary, then drill into specifics.

Broader Significance

Message 1024 is the turning point in this deployment campaign. Before this message, the assistant was executing a well-defined plan: destroy old instances, create new ones with the fixed image, and monitor until they run correctly. After this message, the assistant must confront an unexpected failure mode that requires architectural changes to the benchmark pipeline.

The successful completion of the Norway instance (which happens in subsequent messages) proves that the software stack is sound. The BC instance's failure reveals that the stack has a hardware-dependent memory profile that varies dramatically between the first (uncached) proof and subsequent (cached) proofs. The fix — reducing partition workers for the warmup proof to prevent OOM, then scaling up for cached proofs — represents a significant refinement of the deployment strategy.

This message also illustrates a fundamental truth about distributed systems deployment: you cannot fully predict how software will behave on hardware you don't control. The Vast.ai marketplace offers heterogeneous instances with varying RAM, GPU counts, and network performance. Each combination reveals new failure modes. The assistant's journey through this session — from VAST_CONTAINERLABEL quirks to monitor matching bugs to OOM kills — is a testament to the complexity of deploying compute-intensive workloads on shared infrastructure.

In the end, message 1024 is a reminder that monitoring is not just about collecting data — it is about discovering the questions you didn't know to ask. The assistant went into this check expecting to confirm progress and came out with evidence of a failure that would reshape the entire deployment strategy. The OOM killer, silent and unforgiving, had revealed a hidden constraint that no amount of prior testing had uncovered.