feat: Add Docker-based dynamic domain discovery

[fullpipe]

Hello,

Using ddns with docker most of the time. And it is annoying to update env vars when adding new local domains. So I made use of /var/run/docker.sock. And now it is possible to use ddns like this.

  ddns:
    image: timothyjmiller/cloudflare-ddns:latest
    restart: unless-stopped
    network_mode: host
    environment:
      - DOCKER_HOST=unix:///var/run/docker.sock
    volumes:
      - "/var/run/docker.sock:/var/run/docker.sock:ro"

  api:
    image: "..."
    labels:
      - "ddns.domain=api-local.example.com"
      - "traefik.enable=true"
      - "traefik.http.routers.api.rule=Host(`api-local.example.com`)"

[fullpipe]

P.S.: Have some issues with code formatting. A lot of fixes with simple cargo fmt

$ cargo -V
cargo 1.95.0 (f2d3ce0bd 2026-03-21)
$ cargo fmt --version
rustfmt 1.9.0

[Copilot]

Pull request overview

This RFC introduces Docker-based dynamic domain discovery so the updater can automatically pick up domains from running containers (via a ddns.domain label) instead of requiring manual DOMAINS env var updates.

Changes:

• Adds a Docker scanner (using bollard) that periodically reads container labels and publishes an updated domain set through a tokio::sync::watch channel.
• Threads the dynamic domain set into the update loop by changing updater::update_once to accept a domains map per cycle.
• Extends env config with DOCKER_HOST to enable Docker-based discovery and updates tests/struct initialization accordingly.

Reviewed changes

Copilot reviewed 6 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/updater.rs	Accepts per-cycle domains input and iterates over it for record updates.
src/main.rs	Sets up a watch channel for domains and optionally spawns the Docker domain scanner.
src/docker.rs	New module: scans Docker containers for ddns.domain labels and updates the watch channel.
src/config.rs	Adds docker_host to AppConfig and loads DOCKER_HOST from env; updates validation/tests.
src/pp.rs	Derives Clone for PP to allow passing it into spawned tasks.
Cargo.toml	Adds the bollard dependency.
Cargo.lock	Locks new transitive dependencies from adding bollard.

Comments suppressed due to low confidence (2)

src/updater.rs:121

• If domains contains an IP type that has no configured provider (e.g., IP6_PROVIDER=none but domains include IPv6), detected_ips will always be empty and the code may proceed to delete records when DELETE_ON_FAILURE=true. This becomes more likely with Docker-discovered domains and can lead to unintended deletions.

        for (ip_type, domains) in domains.iter() {
            let ips = detected_ips.get(ip_type).cloned().unwrap_or_default();

            if ips.is_empty() && !config.delete_on_failure {
                ppfmt.warningf(

src/config.rs:545

• The validation error message for having no update targets doesn’t mention DOCKER_HOST, even though it is now a valid way to configure DNS update targets. This makes misconfiguration harder to diagnose.

    if domains.is_empty() && docker_host.is_none() && waf_lists.is_empty() {
        return Err(
            "No update targets configured. Set DOMAINS, IP4_DOMAINS, IP6_DOMAINS, or WAF_LISTS."
                .to_string(),
        );

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[fullpipe]

Merged it to https://github.com/fullpipe/cloudflare-ddns if some one intrested