npm ci wants a lockfile, so an agent starting from an empty directory cannot use
the example configuration until it has written a whole npm project. This one
runs a server.js on node's own http module with no install step at all, which
makes the shortest loop that exercises all three servers: write a file, start it,
open it in the browser.
It reads the port from PORT as well as from the argument. An agent writing a
server from scratch reaches for process.env.PORT far more readily than for argv,
and a preview listening on the wrong port fails its health check with nothing in
the log to explain why.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Two mistakes in the configuration, both of which stopped squid dead. It refuses
an allowlist that names a host and something above it - registry.npmjs.org beside
.npmjs.org - and the continuation lines that followed were then read as
directives of their own. The domains are now one directive per line, each with a
leading dot so it covers the host and everything under it.
Pointing the logs at /dev/stdout so they would reach `docker logs` was the second
one, and it is not fixable here: squid drops to the proxy user, the container's
stdout is a root-owned pipe, and squid calls being unable to open its log fatal.
They stay at squid's own paths, and the config says where to read them.
Checked against a running proxy rather than by reading: npm, PyPI, pythonhosted
and both Maven hosts tunnel through, example.com is refused, a plain HTTP request
to an allowed host is refused as well, and the access log names the refusal.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
A compose .env file is read literally, so MCP_UID=$(id -u) written there arrives
as those eight characters. What came back was "groupadd: invalid group ID", from
a line four steps into a build - true, but it names neither the variable nor the
file that holds it. The build now refuses with both, and says that the file wants
the output of the command rather than the command.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
A named volume whose mount point is absent from the image is created owned by
root, so the worker - which drops root - could not have written a single copy
into /instances. The failure would have surfaced at the first start_service, as
a refused execution far from the line that caused it. Creating the two
directories in the image and giving them to the runtime user is what makes the
volume inherit that ownership.
The user id follows as a build argument, because one number has to satisfy three
things at once: who the process is, who owns the volumes, and who owns the
workspace directory on the host. Left hardcoded, changing MCP_UID to match a
deployment's own user would have brought the same fault back. The guard around
useradd is for the ordinary case of pointing it at an id the base image already
uses - 1000 is the node user - which is otherwise a build failure.
Verified by building both ways and writing into a fresh volume as 10001 and as
1000, and by checking the image carries node 24, Python 3.11 and OpenJDK 25.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
The allowlist still named the shared service's fixed 5173, from before the dev
server handed a port per execution. Every preview would have started on a port
the browser was not allowed to open, and the failure would have read as a broken
application rather than as a refused origin - the kind of mismatch that is found
by exhausting the other explanations first.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
They were three folders on one laptop: a coding agent with a git history of its
own, and two servers - a development server and a browser - with none at all.
What makes them a stack is what sits between them, and that lived nowhere: the
compose file, the gateway, the egress proxy and the networks that keep the worker
off the internet. So the whole thing is one repository, and the coding agent's
separate history is folded into it rather than kept alongside.
What is deliberately absent: .env, node_modules, and the live service
definitions. The .example files next to them say what belongs there.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Lucio Lelii