How Docker Internal DNS Resolution Works | Generated by AI

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There it is. Here’s how it works:

The /etc/hosts in the container

The container’s own hostname (32bb25fb32c8) is listed with all its IPs from each connected network. But LibreChat is NOT in /etc/hosts.

So how does it resolve?

  1. /etc/resolv.conf points to nameserver 127.0.0.11 — that’s Docker’s embedded DNS resolver, running inside every container’s network namespace.

  2. When you do a DNS lookup for LibreChat, it goes to 127.0.0.11, which is Docker’s DNS. Docker knows about all containers on each network — when you docker network connect librechat_default uptime-kuma, the DNS resolver now sees LibreChat on that shared network and returns its IP (172.18.0.6).

  3. If the container wasn’t on librechat_default, Docker’s DNS would not know about LibreChat and the lookup would fail — exactly what happened before.

TL;DR: It’s not /etc/hosts. It’s Docker’s internal DNS at 127.0.0.11 that resolves container names, and it only works when both containers share at least one network.

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