connect: no route to host

What This Error Means

Docker failed to reach the registry due to a network/timeout error.

How to Fix It

1. Retry with debug logs: docker --debug pull <image>.
2. Validate DNS and connectivity to the registry host from the same machine.
3. If you use a proxy, ensure Docker is configured to use it (daemon + CLI env).
4. If the registry is internal, confirm health and TLS cert validity.

Why It Happens

• DNS, firewall, proxy, or VPN is blocking registry traffic.
• The registry is temporarily unavailable or overloaded.
• Corporate proxies are interfering with TLS or long-lived connections.

How to Verify

1. Re-run the original pull/push and confirm it completes.
2. Confirm CI runners can reach the same registry endpoint.

Common CLI Output

connect: no route to host

Prevention Tips

• Use a proxy/cache registry to reduce dependence on upstream availability.
• Keep runner network configuration consistent (DNS/proxy/firewall).