using-docker-in-web

name	using-docker-in-web
description	Set up and use Docker in Claude Code for Web environments. Use when Docker builds fail with bridge/iptables errors, SSL certificate errors through proxy, or when working in containerized web environments.
paths	["**/Dockerfile*","**/docker-compose*.yml","**/docker-compose*.yaml","**/.dockerignore"]

Docker in Claude Code for Web

Claude Code for Web runs in a restricted container environment that requires special configuration for Docker.

Detection

You're in Claude Code for Web if:

# Proxy environment is set
echo $http_proxy  # Shows a proxy URL

# Running inside a container
test -f /.dockerenv && echo "In container"

# iptables is restricted
iptables -L 2>&1 | grep -q "Permission denied"

Quick Setup

# Install Docker
sudo apt-get update && sudo apt-get install -y docker.io

# Start daemon with restrictions (background)
sudo dockerd --iptables=false --bridge=none &

# Wait for daemon to be ready
sleep 3

# Verify
docker info

Building csb Images

Standard builds fail because Docker tries to create bridge networks. Use these flags:

# Build with host networking and insecure SSL (for intercepting proxy)
csb build --host-network --insecure

What these flags do:

• --host-network: Uses host networking instead of bridge (which requires iptables)
• --insecure: Adds -k to curl commands and disables npm strict-ssl (for SSL-intercepting proxies)

Creating Sandboxes

Sandbox creation also needs host networking:

# When creating sandboxes, they'll run in the Docker network
# The proxy container won't work (needs iptables), so use --egress=all
csb create my-sandbox --egress=all

Common Errors and Fixes

"iptables: Permission denied"

The daemon is trying to manage iptables rules. Restart with:

sudo pkill dockerd
sudo dockerd --iptables=false --bridge=none &

"network bridge not found"

Same issue - daemon needs --bridge=none flag.

"SSL certificate problem"

The proxy intercepts HTTPS. Use --insecure flag with csb build, or for manual curl:

curl -k https://example.com

"npm ERR! unable to verify certificate"

npm config set strict-ssl false
npm install
npm config set strict-ssl true  # Reset after

Full Workflow Example

# 1. Install and start Docker
sudo apt-get update && sudo apt-get install -y docker.io
sudo dockerd --iptables=false --bridge=none &
sleep 3

# 2. Build csb images
csb build --host-network --insecure

# 3. Create a sandbox
csb create dev --egress=all

# 4. Connect
csb ssh dev

Limitations

In Claude Code for Web:

• No bridge networking - containers share host network
• No egress proxy container (requires iptables)
• SSL verification must be disabled for builds
• GPU passthrough not available

Cleanup

# Stop all containers
docker stop $(docker ps -q) 2>/dev/null

# Stop daemon
sudo pkill dockerd