OpenCode in Docker: what the container reaches on the network

Introduction

This article is part of a larger manual, OpenCode in Docker on Ubuntu 24.04.

The manual shows how to run OpenCode with the --auto option inside a Docker container.

With --auto the agent does not ask you before each command, so the container limits what it can reach: the agent works only in one git worktree, a separate copy of the project.

The container sees only the files that are mounted into it. The network is different.

This article shows what the container can still reach on the network, and how to close the local site.

What the container reaches

The container goes out through the host, and it reaches the host itself at 172.17.0.1, the gateway of the default Docker network. Checked with wget from the container:

Close the local site

The local site serves the main checkout, ignored files included, so what the worktree of step 2 (a worktree for the agent) kept out is one request away.

Publish its port on 127.0.0.1: the browser on the host keeps working, and the container gets Connection refused:

vi container/docker-compose.yml

php-apache: ports: - "127.0.0.1:8080:80"

Every other port

Every other port gets the same prefix. Each line of this command with 0.0.0.0 or [::] is a service the container can reach:

ss -ltn

The internet stays open. Limiting it to the model's host takes a proxy in front of the container.

Article author: Klavdiya Kondakova