The Debugging Dead-End: When Docker-Compose Says "No Such Service"

A Single Message That Captures the Fragility of Distributed Systems Debugging

In the midst of a complex coding session building a horizontally scalable S3 architecture, there exists a message so brief yet so revealing that it deserves close examination. Message 504 in the conversation reads in its entirety:

[assistant] ## Agent Reasoning kuri-2 is still not running. Let me check the logs to see what's wrong. [bash] FGW_DATA_DIR=/data/fgw2 docker-compose logs kuri-2 2>&1 | tail -40 no such service: kuri-2

Three lines. Two sentences of reasoning. One shell command. One error response. On its surface, this is a trivial moment—an agent trying to debug a failed container and hitting a simple "service not found" error. But beneath this brevity lies a rich tapestry of context, assumptions, debugging strategy, and architectural complexity that makes this message a microcosm of the entire coding session.

The Context: A Cluster in Progress

To understand why this message was written, we must first understand what came before it. The assistant had been building a test cluster for a distributed S3 storage system based on the Filecoin Gateway project. The architecture follows a three-layer hierarchy: stateless S3 frontend proxies on port 8078, independent Kuri storage nodes, and a shared YugabyteDB backend. The critical architectural insight—arrived at after significant debugging—was that each Kuri node needed its own segregated database keyspace for groups, deals, and blockstore data, while sharing only the S3 metadata keyspace for object routing.

The session immediately preceding message 504 had been intense. The assistant had:

1. Implemented node_id filtering across all RIBS database queries to support per-node keyspace isolation
2. Created a NewRibsDBWithConfig wrapper to inject the node ID from configuration
3. Fixed an FX dependency injection issue where the wrong config type was being provided
4. Updated gen-config.sh to generate proper configuration for both kuri-1 and kuri-2
5. Rebuilt the Docker image successfully
6. Cleaned the data directory and regenerated configuration
7. Started the cluster with ./start.sh /data/fgw2 The user had also contributed critical context: the public address is filecoingateway.devtty.eu, and the start.sh script has an interactive first-time initialization step that the assistant should not attempt to automate. So when message 504 arrives, the assistant is in a state of expectation. It has done the work. The cluster should be running with both nodes. But something is wrong.

The Reasoning: A Logical Debugging Reflex

The assistant's reasoning is straightforward and entirely rational: "kuri-2 is still not running. Let me check the logs to see what's wrong." This is debugging instinct at its most fundamental. When a service fails to start in a Docker Compose environment, the first diagnostic step is always to check the logs. The assistant correctly identifies the target (kuri-2), the tool (docker-compose logs), and the scope (tail -40 to get the most recent output).

The phrase "still not running" is telling. It reveals that the assistant had already observed the failure state—likely from the startup output of start.sh or from a quick docker ps check—and is now moving to the investigation phase. There is no panic, no confusion about what to do next. The debugging methodology is clean and disciplined.

The Assumptions: Where Things Go Wrong

Every debugging step rests on assumptions, and message 504 reveals several that turn out to be incorrect.

Assumption 1: The service is named "kuri-2" in docker-compose. This is the most critical assumption, and it is wrong. The command docker-compose logs kuri-2 returns "no such service: kuri-2," meaning the service name in the docker-compose.yml file does not match what the assistant expects. This could be because the service was defined under a different name (perhaps "kuri2" without the hyphen, or a fully qualified name like "kuri-node-2"), or because the docker-compose.yml was not properly updated when the assistant enabled the second node in message 479.

Assumption 2: The docker-compose command is being run from the correct directory. The assistant sets FGW_DATA_DIR=/data/fgw2 as an environment variable but does not explicitly cd to the test-cluster directory before running the command. Earlier in the conversation (message 502), the assistant encountered a "no such file or directory" error when trying to run ./start.sh from the wrong directory. The same pattern may be repeating here—the assistant might be running docker-compose from a directory that does not contain the docker-compose.yml file, or from a directory where a different docker-compose.yml is in effect.

Assumption 3: The container actually started and generated logs. The assistant assumes that kuri-2 was instantiated by Docker Compose and that there are logs to read. But if the service definition is missing or misconfigured, no container was ever created, and there are no logs to fetch. The "no such service" error is Docker Compose's way of saying "I don't know what you're talking about."

Assumption 4: The debugging context is still valid. The assistant assumes that the state of the cluster is the same as when start.sh was invoked. But between the startup and this debugging command, the containers may have already exited, been cleaned up, or entered a different lifecycle state.## The Thinking Process: From "No Such Service" to Root Cause

What makes message 504 so fascinating is not what it says, but what it reveals about the assistant's thinking process when viewed alongside the messages that immediately follow. The assistant receives "no such service: kuri-2" and does not panic. Instead, it executes a textbook debugging progression:

Message 505: "The service name might be different. Let me check what services are running." The assistant runs docker-compose ps and gets an empty table—no services at all. This is a second surprise, deepening the mystery.

Message 506: "Hmm, no services are showing. Let me check if docker-compose is using the right file." The assistant explicitly passes -f docker-compose.yml to rule out the possibility that Docker Compose is looking at a different file. Still empty. This is a critical moment: the assistant is questioning its own assumptions about the environment.

Message 507: "The containers might have already exited. Let me check all containers including stopped ones." The assistant switches from docker-compose ps to docker ps -a, which bypasses Docker Compose's abstraction layer entirely and queries the raw Docker daemon. This is the breakthrough. The raw output shows that containers do exist—test-cluster-s3-proxy-1 is running, test-cluster-kuri-2-1 exited with error code 1. The problem was that Docker Compose was not managing these containers, likely because the assistant was running docker-compose commands from outside the project directory or without the correct compose file context.

Message 508: The assistant directly inspects the exited container's logs using docker logs test-cluster-kuri-2-1 and finds the real error: Configuration load failed: %w RetrievableRepairThreshold greater than MinimumReplicaCount: 3 > 1. This is the genuine root cause—a configuration validation error where the repair threshold exceeded the replica count.

This debugging sequence is a masterclass in layered troubleshooting. Each step questions a deeper assumption: first the service name, then the compose file path, then the Docker Compose abstraction itself. The assistant demonstrates the crucial skill of knowing when to abandon a tool's abstraction layer and go directly to the underlying system.

Input Knowledge Required

To understand message 504, a reader needs substantial domain knowledge:

Docker Compose fundamentals: The reader must understand that docker-compose logs <service> fetches logs for a named service defined in a docker-compose.yml file. They must also understand that service names are case-sensitive and must exactly match the definition in the YAML file.

The project architecture: The reader needs to know that this is a three-layer S3 storage system with Kuri nodes as the storage layer. "kuri-2" refers to the second storage node in a test cluster. The assistant had just enabled this node after implementing per-node database keyspace isolation.

The debugging context: The reader must understand that FGW_DATA_DIR is an environment variable used by the Docker Compose file to locate data directories, and that the assistant had just run start.sh which should have started both nodes.

The conversation history: This message is meaningless without knowing that the assistant had been fighting with configuration issues, FX dependency injection problems, and database keyspace segregation for the preceding messages.

Output Knowledge Created

Message 504 itself creates very little output knowledge—it is a debugging dead-end that produces only an error message. However, it creates significant process knowledge:

1. The service name assumption is wrong. The assistant learns that kuri-2 is not a valid Docker Compose service name in the current context. This triggers the deeper investigation that follows.
2. Docker Compose context matters. The error implicitly teaches that Docker Compose commands are context-dependent and that running them from the wrong directory or without the correct configuration file will produce misleading errors.
3. The cluster state is not as expected. The assistant learns that its mental model of the cluster (both nodes running) does not match reality. This mismatch drives the subsequent investigation.

Mistakes and Incorrect Assumptions

Several assumptions in message 504 turn out to be incorrect or incomplete:

The most significant mistake is the assumption that docker-compose logs is the right tool for the job. In this case, Docker Compose did not know about the kuri-2 service because the containers had been started outside of Docker Compose's tracking (perhaps by start.sh using raw docker run commands, or by Docker Compose running from a different directory). The assistant correctly pivoted to docker ps -a in message 507, but the initial approach wasted a round-trip.

The assistant assumes the service name matches the docker-compose.yml definition. This is a reasonable assumption—the assistant had edited docker-compose.yml in message 479 to enable kuri-2. But the assumption does not account for the possibility that the edit was incomplete, that the file was not saved, or that a different docker-compose.yml was being used.

The assistant assumes the container lifecycle is still active. By the time the debugging command runs, kuri-2 has already exited (as shown in message 508, it exited 33 seconds ago). The assistant does not consider that the container might have already been garbage-collected or removed by a cleanup process.

The assistant does not verify its working directory. Earlier in the conversation (message 502), the assistant ran a command from the wrong directory and got "no such file or directory." The same pattern may be repeating here. The assistant does not explicitly cd to the test-cluster directory before running the docker-compose command, relying instead on the FGW_DATA_DIR environment variable for context.

The Deeper Meaning: A Microcosm of Distributed Systems Debugging

Message 504, for all its brevity, captures something profound about debugging distributed systems. The error message "no such service: kuri-2" is technically correct but practically misleading. The service does exist—it was defined in docker-compose.yml, it was started by start.sh, and its container is visible in docker ps -a. But Docker Compose cannot see it because of a context mismatch.

This is the essence of distributed systems debugging: the tools we use to observe the system are themselves part of the system, subject to the same configuration errors, context dependencies, and abstraction leaks as the services they monitor. The assistant's debugging journey from "no such service" to the real configuration error (RetrievableRepairThreshold > MinimumReplicaCount) is a perfect example of the detective work required when the observation tool itself is unreliable.

The message also reveals the assistant's debugging philosophy: start with the simplest diagnostic, accept the result even when it contradicts expectations, and iteratively refine the approach. There is no frustration in the reasoning, no insistence that the tool must be wrong. Just a calm, methodical progression: "Let me check the logs. Oh, that didn't work. Let me check what services are running. Still empty. Let me check the raw containers. There it is."

In the end, message 504 is a testament to the fact that in complex systems, the most valuable debugging skill is not knowing the right answer, but knowing how to ask the right questions—and being willing to abandon your assumptions when the answers don't make sense.