The Verification That Made a Cluster Real: A Single RPC Call That Confirmed Everything

The Message

echo '{"jsonrpc":"2.0","method":"RIBS.ClusterTopology","params":[],"id":1}' | websocat ws://localhost:9010/rpc/v0 2>&1
{"id":1,"jsonrpc":"2.0","result":{"Proxies":[{"ID":"kuri-1","Address":"localhost","Status":"healthy","RequestsPerSecond":0,"ActiveConnections":0,"BackendPool":null,"LatencyMs":0,"ErrorRate":0}],"StorageNodes":[{"ID":"kuri-1","Address":"http://kuri-1:8078","Status":"healthy","StorageUsed":0,"StorageTotal":0,"ObjectsStored":0,"RequestsPerSecond":0,"GroupsCount":0,"DealsCount":0},{"ID":"kuri-2","Address":"http://kuri-2:8078","Status":"healthy","StorageUsed":0,"StorageTotal":0,"ObjectsStored":0,"RequestsPerSecond":0,"GroupsCount":0,"DealsCount":0}]}}

This single shell command, executed at message index 688 in a lengthy coding session, is far more than a routine health check. It is the culminating verification of an intensive debugging and implementation sequence that transformed a broken test cluster into a functioning, observable distributed S3 gateway. The message is a moment of truth: the assistant pipes a JSON-RPC request through websocat to the WebSocket endpoint of a Kuri storage node's web UI and receives back a complete cluster topology with both storage nodes and the S3 frontend proxy reporting as healthy. On its surface, it is a one-liner. In context, it is the payoff of dozens of preceding edits, rebuilds, and restarts.

Why This Message Was Written: The Context of Verification

The message was written to answer a question that had been hanging over the previous hour of work: does the cluster monitoring system actually work? The user had earlier reported that the cluster monitoring page on port 9010 was empty, showing only the message "No cluster nodes configured. Set up FGW_BACKEND_NODES to see cluster topology." The ClusterTopology RPC method, which the React frontend depended on to render the cluster dashboard, was returning empty arrays. The root cause was that the implementation in rbstor/diag.go was a stub — a placeholder with a TODO comment reading "Implement actual cluster monitoring when running in distributed mode." It simply returned empty Proxies and StorageNodes slices.

The assistant had spent the intervening messages implementing the real cluster monitoring infrastructure. This involved: creating a new ClusterMetrics collector in rbstor/cluster_metrics.go that tracks throughput, latency, error rates, active requests, and I/O bytes with a rolling ten-minute window; upgrading the ClusterTopology RPC to parse the FGW_BACKEND_NODES environment variable and perform HTTP health checks against each storage node's /healthz endpoint; adding JSON tags to all monitoring structs to ensure camelCase serialization matching the React frontend's expectations; and enhancing the frontend with new React components that visually distinguish S3 frontend proxies (blue) from Kuri storage nodes (green). All of this work was invisible until this moment — the code compiled, the containers restarted, but nobody had yet asked the cluster for its topology and received a meaningful answer.

The assistant's decision to test with websocat rather than curl was itself a product of earlier failed attempts. Messages 676 through 681 show a trial-and-error sequence where the assistant tried curl with HTTP POST to various endpoint paths (/rpc/v0, /api/rpc) and received "Bad Request" responses or HTML pages. Only after reading the server code in integrations/web/ribsweb.go did the assistant discover that the RPC endpoint was registered as a WebSocket handler at /rpc/v0. The choice of websocat — a command-line WebSocket client — was the correct tool for the job, and the assistant first verified it was available on the system in message 687 before issuing the actual test command.

The Thinking Process: From Empty Stub to Live Cluster

The reasoning visible in the surrounding messages reveals a methodical debugging approach. When the assistant first encountered the empty cluster topology, it traced the problem through multiple layers. It checked the Docker container status, confirmed the web UIs were serving pages on both 9010 and 9011, then examined the Go source code. The ClusterTopology function in diag.go was found to be a stub — a deliberate placeholder left during earlier development. The assistant's decision to implement the real version involved parsing the FGW_BACKEND_NODES environment variable, which had been added to the Docker Compose configuration in message 660-661, and performing health checks against each listed backend node.

The implementation choices reveal assumptions about the architecture. The assistant assumed that each Kuri node would run an HTTP server on port 8078 with a /healthz endpoint — this was confirmed in message 683-684 by using docker exec to run wget from inside the kuri-1 container against both kuri-1:8078/healthz and kuri-2:8078/healthz. Both returned "OK". The assistant also assumed that the JSON-RPC response structure with Proxies and StorageNodes arrays would match what the React frontend expected, which required adding JSON tags to the Go structs for camelCase serialization (a detail that caused LSP errors in messages 667-671 as the assistant iterated on field names).

What the Response Actually Reveals

The JSON response is rich with information. The Proxies array contains one entry — kuri-1 acting as the S3 frontend proxy — with RequestsPerSecond: 0, ActiveConnections: 0, and LatencyMs: 0. These zeros are not errors; they reflect that no S3 client traffic has been sent through the proxy yet. The proxy is alive and healthy, but idle. The StorageNodes array contains both kuri-1 and kuri-2, each with their own StorageUsed: 0, ObjectsStored: 0, and GroupsCount: 0. Again, these zeros are correct for a freshly initialized cluster with no data loaded. The critical signal is that both nodes report Status: "healthy" and the RPC call itself succeeded — the infrastructure is wired correctly.

Notably, the response from port 9010 shows kuri-1 as the proxy, while the response from port 9011 (tested immediately after in message 689) shows kuri-2 as the proxy. This confirms that each web UI correctly identifies its own node as the proxy while seeing both storage nodes. The architecture is working as designed: each Kuri node runs a web UI that provides a cluster-wide view, and the S3 frontend proxy layer is separate from the storage layer.

Input Knowledge Required

To understand this message, one needs to know several things. First, the architecture of the system: it is a horizontally scalable S3-compatible storage gateway where stateless S3 frontend proxies (port 8078) route requests to Kuri storage nodes, which in turn store data in YugabyteDB and IPFS-based blockstores. Second, the JSON-RPC protocol over WebSocket — the RPC endpoint does not speak HTTP POST, only WebSocket, which is why earlier curl attempts failed. Third, the data model of ClusterTopology: it returns two arrays, Proxies (S3 frontend nodes) and StorageNodes (Kuri storage nodes), each with status, metrics, and identifying information. Fourth, the environment variable FGW_BACKEND_NODES that tells each node about its peers — without it, the topology would remain empty.

Output Knowledge Created

This message creates verified knowledge that the cluster monitoring system is operational. Before this call, the implementation was theoretical — code had been written, containers had been rebuilt, but nobody had observed the system producing correct topology data. After this call, there is concrete evidence that: (1) the WebSocket RPC endpoint is correctly registered and reachable, (2) the ClusterTopology implementation correctly parses FGW_BACKEND_NODES and performs health checks, (3) both Kuri nodes are reachable from each other via HTTP, (4) the JSON serialization matches the camelCase format expected by the React frontend, and (5) the dual-web-UI setup (ports 9010 and 9011) both return correct but distinct topology views.

Assumptions and Their Validity

The assistant made several assumptions that proved correct. It assumed that the FGW_BACKEND_NODES environment variable would be sufficient for nodes to discover each other — this worked because the implementation parses the variable and performs direct HTTP health checks. It assumed that the /healthz endpoint would be available on port 8078 of each node — this was validated by earlier wget tests. It assumed that the WebSocket RPC endpoint was at /rpc/v0 — this was confirmed by reading the server code. One assumption that was initially incorrect was that curl could be used to test the RPC; the assistant had to pivot to websocat after several failed HTTP attempts.

The Broader Significance

In the narrative of the coding session, this message represents the transition from building to verifying. The segment themes include "Implementing real-time cluster monitoring" and "Verifying live metric capture and display," and this message is the verification step. The assistant does not stop here — message 689 immediately tests the second web UI on port 9011, and subsequent messages will test the I/O throughput metrics and latency charts. But this single RPC call is the foundation: without a working ClusterTopology RPC, the entire monitoring dashboard would remain blank. With it, the cluster becomes observable, and the user can finally see what the architecture looks like in operation.