The Proxy Epiphany: Recognizing Architectural Boundaries in a Distributed S3 Deployment

Introduction

In the course of deploying a QA test cluster for the Filecoin Gateway (FGW) distributed storage system across three physical nodes, a single message from the assistant marked a critical turning point. After successfully deploying two kuri storage nodes, configuring shared YugabyteDB databases, and verifying that both nodes appeared healthy in the cluster topology, the team hit a stubborn problem: objects written to one node could not be read from the other. The assistant's message at index 2069 represents the moment of architectural recognition—the realization that the current design, with kuri nodes acting as direct S3 endpoints, could never support cross-node reads without an additional routing layer. This insight triggered the deployment of the s3-proxy frontend, fundamentally reshaping the cluster architecture.

The Message in Full

The subject message reads:

The error says "block was not found locally (offline)" - it's trying to find the block locally, not doing network retrieval. This is by design - the S3 server serves data from the local blockstore. For multi-node, you need the s3-proxy frontend which routes requests to the correct backend node.

Let me check if we should deploy s3-proxy: [bash] ls -la /home/theuser/gw/s3-proxy 2>/dev/null && /home/theuser/gw/s3-proxy --help 2>&1 | head -20 -rwxr-xr-x 1 theuser theuser 39182056 Jan 31 22:58 /home/theuser/gw/s3-proxy Failed to load configuration: invalid log level:

This brief exchange—barely a dozen lines of text—contains a profound shift in understanding. It moves from debugging a symptom to recognizing a fundamental architectural constraint, and then immediately pivots to verifying the availability of the correct solution.

The Path to This Realization

To understand why this message was written, we must trace the debugging journey that preceded it. The user had deployed a QA cluster with two kuri nodes (kuri1 at 10.1.232.83, kuri2 at 10.1.232.84) and a head node running YugabyteDB. Initial verification showed both nodes healthy, and the cluster topology API returned proper data after configuring the FGW_BACKEND_NODES environment variable.

The user then asked to run the loadtest tool against the cluster. The assistant ran it against kuri1's S3 endpoint on port 8079, and the user immediately spotted a problem: only kuri1 was receiving traffic. This observation triggered a series of cross-node read tests. The assistant wrote a test object to kuri1 and attempted to read it from kuri2. The read returned empty. Further investigation revealed that kuri2 could see the object's metadata in the shared filecoingw_s3 CQL keyspace—the S3 objects table stored entries with a node_id field identifying which node held the data—but the actual block data was absent.

The assistant initially attempted to solve this through bitswap, the IPFS peer-to-peer block exchange protocol. By connecting the two kuri nodes' IPFS swarm peers, the assistant hoped that kuri2 would be able to fetch the block from kuri1 over the peer-to-peer connection. The swarm connect succeeded, but the cross-node read still returned empty. The error log on kuri2 was unambiguous: "block was not found locally (offline): ipld: could not find bafkreicq725qu5x2tcre6ff6jb7cbuu4msnmmdceannrzsk6spdmom3gb4."

This is the critical moment captured in message 2069. The assistant reads that error and finally interprets it correctly: the S3 server is not attempting network retrieval at all. It is serving data exclusively from the local blockstore.## The Reasoning: From Symptom to Architectural Insight

The assistant's reasoning in this message is a model of diagnostic discipline. The error message—"block was not found locally (offline)"—had appeared before, but the assistant had not fully absorbed its implications. Earlier attempts to fix cross-node reads had focused on bitswap peering, assuming that if the nodes were connected via IPFS's libp2p swarm, block retrieval would happen automatically. The swarm connect succeeded, yet reads still failed.

The key insight in message 2069 is the phrase "This is by design." The assistant recognizes that the behavior is not a bug or a misconfiguration, but an intentional architectural choice. The S3 server in the kuri node is designed to serve data from the local blockstore only. It does not implement a distributed retrieval mechanism for S3 requests. The separation of concerns is deliberate: storage nodes store and serve their local data, while a separate proxy layer handles routing and distribution.

This realization represents a shift from a "fix the node" mindset to a "fix the architecture" mindset. The assistant stops trying to make kuri nodes do something they were never designed to do, and instead looks for the component that was designed for exactly this purpose: the s3-proxy frontend.

Assumptions Made and Corrected

Several assumptions underlay the earlier debugging attempts, and message 2069 represents the moment those assumptions were corrected:

Assumption 1: Bitswap would enable cross-node S3 reads. The assistant assumed that connecting the two kuri nodes' IPFS swarms would allow kuri2 to fetch blocks from kuri1 when serving S3 GET requests. This assumption was reasonable given that bitswap is the standard mechanism for IPFS block exchange. However, the S3 server implementation does not integrate with bitswap for S3 operations—it only looks in the local blockstore. The assistant's message explicitly corrects this: "it's trying to find the block locally, not doing network retrieval."

Assumption 2: The error indicated a networking or connectivity issue. Earlier, the assistant had tried various network-level fixes: checking peer IDs, establishing swarm connections, and verifying that the nodes could communicate. The persistent error suggested to the assistant that something was wrong with the connection. Message 2069 reframes the error as a design constraint rather than a connectivity failure.

Assumption 3: The cluster topology configuration would enable distribution. The assistant had configured FGW_BACKEND_NODES on both kuri nodes, which made the topology API work correctly. But this configuration was for the diagnostic/monitoring layer, not for the S3 data routing layer. The assistant had conflated two different configuration domains.

Input Knowledge Required

To fully understand message 2069, one needs knowledge of several domains:

Distributed storage architecture patterns, specifically the distinction between storage nodes (which hold data) and proxy/frontend nodes (which route requests). The assistant draws on this architectural knowledge to recognize that the current setup is missing a layer.
The FGW system architecture, including the existence of the s3-proxy component. The assistant knows that such a binary exists and where it lives in the build output. The fact that the assistant checks for /home/theuser/gw/s3-proxy indicates prior knowledge of this component's role.
S3 protocol semantics, specifically that S3 operations are request-response and do not inherently support distributed retrieval. Each S3 endpoint serves its own storage.
The error log format and meaning from the kuri daemon. The assistant reads "block was not found locally (offline)" and understands that "offline" refers to the blockstore's internal state, not the node's network connectivity.
The build and deployment toolchain, including where binaries are compiled and how to check their existence and help output.## Output Knowledge Created Message 2069 produces several valuable pieces of output knowledge that advance the deployment effort: First, it establishes a clear architectural diagnosis: the S3 server in kuri nodes serves only from the local blockstore. This is not a bug that can be fixed through configuration or network tuning—it is a design invariant that must be accommodated by adding a new layer. Second, it identifies the correct solution: the s3-proxy frontend. The assistant immediately verifies that the binary exists at /home/theuser/gw/s3-proxy and is approximately 39 MB in size, confirming it was already compiled. The --help output reveals a configuration error ("invalid log level") but confirms the binary is present and functional. Third, it establishes a decision point. The rhetorical question "Let me check if we should deploy s3-proxy" is followed by an immediate action—checking the binary. In practice, this is a statement of intent: the assistant has already decided that deploying s3-proxy is the correct next step, and is verifying prerequisites. Fourth, the message implicitly documents a key architectural rule for the FGW system: S3 read requests must go through the proxy layer to reach the correct backend node. This rule was not explicitly stated in earlier documentation or configuration, but is now discovered through empirical debugging.

The Thinking Process

The reasoning visible in this message follows a clear diagnostic arc:

Error interpretation: The assistant reads the error log from kuri2 and extracts the critical phrase "block was not found locally (offline)." The word "locally" is the key—it indicates the search scope, not the node's network status.
Design inference: From this error, the assistant infers the design principle: "the S3 server serves data from the local blockstore." This is not stated in any configuration file or documentation visible in the session—it is deduced from the behavior.
Architectural mapping: The assistant maps this design principle to the known system architecture, recognizing that a separate s3-proxy component exists for multi-node routing. The phrase "For multi-node, you need the s3-proxy frontend" connects the observed behavior to the system's intended architecture.
Action planning: The assistant immediately moves from diagnosis to verification, checking whether the s3-proxy binary exists and is functional. This is a pragmatic, execution-oriented response—no time is spent lamenting the failed bitswap approach or analyzing why it didn't work. What is notably absent from this message is any self-criticism or backtracking about the earlier bitswap attempt. The assistant does not say "I was wrong to try bitswap" or "I should have realized this sooner." Instead, it treats the discovery as new information that changes the plan going forward. This is a characteristic of effective debugging: treating each failed hypothesis not as a mistake but as data that constrains the solution space.

Broader Significance in the Deployment Context

This message sits at a pivotal moment in the QA cluster deployment. The session had already overcome several major hurdles: dirty CQL migration states that prevented kuri from starting, missing environment variables that caused empty topology responses, and S3 authentication issues with unsigned payloads. Each of these was a configuration or state problem that could be fixed by adjusting settings or clearing flags.

The cross-node read problem was different. It was not a configuration gap but an architectural gap. The system as deployed was missing a component—the s3-proxy—that was essential for the multi-node use case. This required not a configuration change but a deployment change: adding a new service, configuring it, and integrating it into the existing infrastructure.

The assistant's subsequent actions (deploying s3-proxy on the head node, configuring it with CQL hosts and backend node list, setting it up as a systemd service via Ansible) represent the culmination of this insight. The proxy becomes the single point of entry for S3 requests, routing each request to the correct backend node based on the object's stored node_id metadata. After this deployment, the load test showed both nodes receiving traffic, confirming that cross-node reads were working correctly.

Conclusion

Message 2069 is a study in architectural recognition under pressure. Faced with a persistent error that resisted network-level fixes, the assistant stepped back from the details of the error message and recognized a fundamental design constraint. The insight—that the S3 server serves only from the local blockstore by design—transformed the debugging approach from "fix the node" to "add the missing layer." This kind of architectural thinking, where a practitioner recognizes when a problem cannot be solved within the current layer and requires a new structural element, is one of the most valuable skills in distributed systems engineering. The message captures that moment of recognition in its purest form: a clear diagnosis, a named solution, and an immediate verification step.