Avoiding Docker Daemon Proxy Loops | Generated by AI

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Why "no-proxy": "localhost,127.0.0.1,.local" is Crucial in Docker’s daemon.json

When you configure Docker’s daemon with proxy settings like "http-proxy": "http://localhost:7890" (common for tools like Clash running locally), the daemon applies these rules to all outgoing network traffic by default. This includes connections to external registries (e.g., registry-1.docker.io for pulling images like hello-world).

However, without the no-proxy directive, Docker daemon also tries to route local connections—such as the initial TCP handshake to your proxy server itself at localhost:7890—through the same proxy. This creates a classic proxy loop:

  1. Docker needs to fetch an image from registry-1.docker.io.
  2. It attempts to connect via the proxy at localhost:7890.
  3. But to reach localhost:7890, the proxy settings kick in again, forcing Docker to… connect via the proxy at localhost:7890.
  4. This infinite recursion fails at the TCP level because the proxy can’t proxy a connection to itself (it leads to a self-referential loop with no resolution).
  5. The connection aborts unexpectedly, resulting in the proxyconnect tcp: EOF error (EOF means “end of file,” signaling a premature closure during the proxy negotiation/handshake).

Adding "no-proxy": "localhost,127.0.0.1,.local" explicitly tells the daemon to bypass the proxy for traffic destined to:

This allows Docker to connect directly to the proxy server on localhost without looping through itself. Once connected, the proxy can then handle the external request to the Docker registry properly (e.g., via HTTP CONNECT for HTTPS traffic).

In short: It prevents the daemon from “proxying the proxy,” ensuring local proxy access works while still routing internet-bound traffic (like image pulls) through it.

If your setup involves other local services (e.g., internal registries or containers communicating locally), extending no-proxy with those domains/IPs can prevent similar issues.

Docker Daemon Proxy Configuration
Docker Proxy Settings Forum Discussion
Docker Proxy Guide for Corporate Firewalls

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