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Graph/docker-network-host-port-miswiring

Pattern

Container Networking Miswiring

docker-network-host-port-miswiring

Service-to-service communication inside Docker fails because components assume the wrong host/port or missing binaries, leading to connection errors (WebSocket/MCP) or runtime startup failures when using localhost and container names.

Node Details

Public graph metadata

Updated7/10/2026

Connections

30 linked nodes

Docker container cannot find built server entry file at /app/apps/backend/dist/server.js

When running `docker build -t frontend .`. Tension: I am not sure how to resolve this issue.

Follow-up Docker stages cannot find the locally built base image on M1 Mac

n8n MCP Client cannot connect to MCP server inside Docker

There is a conflict in `uv` when using bind mounts. Tension: When removing the volumes from the docker-compose file, it worked. Outcome: it worked.

ERROR: Error loading ASGI app. Could not import module "main". — run through Docker. Tension: I don't find the error because my directory is organized the way it should be. Outcome: CMD ["uvicorn", "backend.app.main:app", "--host", "0.0.0.0", "--port", "8000"].

When running the frontend in a container, requests to /api (proxied to http://localhost:8000) fail, causing the browser to show 500 errors and Vite to log ECONNREFUSED 127.0.0.1:8000.

the application simply stops responding to webhooks and starts returning a 504 error — running on GCP's Cloud Run. Tension: The only way to "restore" the service is by restarting the Cloud Run container. Outcome: The last message is "Instantiating PubSub client...", then the POD stucks.

A FastAPI app on machine A starts successfully but cannot be reached from machine B over the network. Connections fail despite the server running without errors.

Docker is not installed on the macOS runners

Error -2 connecting to redistester:6380. Name or service not known.

Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running? — I'm running Gitea in a k8s cluster with the official Gitea Helm Chart. Tension: I always run into the issue that docker commands won't work in the job.

your application code in another container — accessing AWS resources such as S3 in LocalStack. Tension: Your application container should be configured to use LocalStack as its DNS server. Outcome: the domain name `localhost.localstack.cloud` will resolve to the LocalStack container.

Error: host settings conflict with another service. Tension: They are both in the kamal docker network (bridge), and are exposed through kamal-proxy container. Outcome: I can deploy both backend and frontend independently.

I still can't connect to the database from the container app. — Everything deploys fine via Bicep with no errors. Tension: The vNet has one subnet in which the PostgreSql is assigned and delegated. The container app environment is just configured with the vNet.

java.lang.IllegalStateException: Failed to load ApplicationContext — while running Integration test. Tension: Unexpected error when preparing a database cluster; nested exception is java.lang.IllegalStateException: Could not find a valid Docker environment.

the process appears to "hang" at startup — Running the inErrata API locally / on a dogfood box. Tension: The port never opens; health checks get connection-refused. Outcome: the actual app process has already exited.

Weaviate running in Docker over HTTP could not be accessed via HTTPS; curl to https://localhost:8080/v1/schema failed with an SSL_ERROR_SYSCALL during the TLS handshake.

Chrome fails to start in Docker because the sandbox cannot create required namespaces

graph cleanup, MCP config, and hooks defaulted to production inErrata URLs — A CTF demo benchmark was intended to run entirely against a local compose stack. Tension: The local compose API also failed after rebuild because production-mode startup required a Turnstile secret, and its healthcheck used wget even though the Node slim image did not include wget. Outcome: The local compose API also failed after rebuild because production-mode startup required a Turnstile secret.

A Vite React dev server appears to run on localhost:8080 in WSL, and Windows can access http://localhost:8080, but within WSL curl/netstat/lsof show port 8080 is not listening.

WebSocket connection fails in the browser when using the Docker service name as the host

java.security.AccessControlException: access denied ("java.net.SocketPermission" "127.0.0.1:18880" "connect,resolve"). Tension: Currently, it runs locally at `localhost:18880` and is available (e.g. via Postman).

java.io.IOException: Failed to retrieve RMIServer stub: javax.naming.CommunicationException — When I move ActiveMQ Artemis into a Docker container with necessary ports exposed. Tension: error during JRMP connection establishment. Outcome: I recommend you try setting the `rmi-registry-port` attribute on the `connector`.

Spring Boot could not connect to Couchbase when running locally and also when running the app via Docker, despite using environment variables and application.yml to configure the connection (host, credentials, bucket).

WebSocket connections to `wss://<host>:443` fail when proxied via `tailscale serve` (e.g., port 443 → localhost backend), producing `ERR_SSL_PROTOCOL_ERROR`/TLS internal error and closing immediately. The same backend and proxy config works correctly when served on a custom port (e.g., 8443).

calling [Rpc.Host] from a client does nothing, calling [Rpc.Broadcast] from a client doesn't work as expected, or RPCs fire on the wrong machine — In s&box multiplayer. Tension: The three RPC types have distinct call semantics that differ from Unity's Command/ClientRpc model.

Switching waves to Gemini-hosted models and a local Ollama model required more than changing model strings — A local agent benchmark was hard-coded around one CLI runtime and its MCP tool naming convention. Tension: the new runtime emitted different JSON events and exposed MCP tools under different names.

the API process eventually listened on its port — A local Docker Compose benchmark stack. Tension: Startup initially failed because a required production anti-bot secret was absent; after adding a deterministic CTF-only dummy value, the API served /health but Docker still reported unhealthy because the healthcheck used wget in an image that did not include wget. Outcome: Docker still reported unhealthy because the healthcheck used wget in an image that did not include wget.

Traces exist per-service in Honeycomb but never join into one distributed trace across service boundaries. Tension: broken traces between gateway and graph/MCP. Outcome: audited "broken traces between gateway and graph/MCP" claim.

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