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Moving a container image from Alpine to Debian Bookworm can improve compatibility with dependencies such as Playwright or Python 3.13. However, minimal Debian images may introduce a name resolution failure that breaks communication through localhost.

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Symptom

A sandbox that worked on Alpine may enter a crash loop after switching to an image such as node:22-bookworm-slim. Its logs show an error like:
The error can occur even when sandbox-api is running because the system cannot resolve localhost to a loopback address.

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Root cause

Slim or minimal Debian distributions may omit the /etc/hosts entry or name service configuration in nsswitch.conf that resolves localhost. When an application or a utility such as netcat (nc) connects to localhost, the system performs a name lookup. Without an explicit hosts mapping or suitable resolver configuration, that lookup fails with getaddrinfo before the request reaches the network stack.

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Use the loopback IP

Replace localhost with 127.0.0.1 in entrypoint scripts, health checks, and tool server configurations. Using the explicit loopback address bypasses hostname resolution. Configure clients to connect to 127.0.0.1. Configure servers to listen on 0.0.0.0 when they must also be reachable through external container ports.

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Check a Debian migration

When moving from Alpine to bookworm-slim:
  • Install ca-certificates explicitly to prevent Git clone and HTTPS failures
  • Replace localhost with 127.0.0.1 in internal scripts
  • Verify that EXPOSE instructions and port mappings, such as port 8081 for an internal API, match your infrastructure

Sandbox proxy and network

Learn how networking works inside Blaxel sandboxes.

Sandbox ports

Configure ports exposed by sandbox services.
Last modified on October 5, 2026