feat: sync Cloudflare DNS records with Traefik container hosts

Create a record for each Host(...) in running containers' Traefik router
labels, tagged with a configurable comment and optional tags, and delete
owned records once their host has been down for DELETE_AFTER.

.dockerignore

@@ -0,0 +1,4 @@
+.git
+.github
+.env
+*.md

.github/workflows/ci.yml

@@ -0,0 +1,54 @@
+name: ci
+
+on:
+  push:
+    branches: [main]
+    tags: ["v*.*.*"]
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+      - uses: actions/setup-go@v6
+        with:
+          go-version-file: go.mod
+      - run: test -z "$(gofmt -l .)"
+      - run: go vet ./...
+      - run: go test -race ./...
+
+  image:
+    needs: test
+    if: github.event_name == 'push'
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - uses: actions/checkout@v5
+      - uses: docker/setup-buildx-action@v3
+      - uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ghcr.io/${{ github.repository }}
+          tags: |
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=semver,pattern={{major}}
+            type=edge,branch=main
+      - uses: docker/build-push-action@v6
+        with:
+          context: .
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}

.gitignore

@@ -0,0 +1,4 @@
+.env
+/traefik-cloudflare-dns
+*.test
+*.out

Dockerfile

@@ -0,0 +1,11 @@
+FROM --platform=$BUILDPLATFORM golang:1-alpine AS build
+ARG TARGETOS TARGETARCH
+WORKDIR /src
+COPY go.mod ./
+COPY *.go ./
+RUN CGO_ENABLED=0 GOOS=$TARGETOS GOARCH=$TARGETARCH go build -trimpath -ldflags="-s -w" -o /out/traefik-cloudflare-dns .
+
+FROM gcr.io/distroless/static-debian12:nonroot
+COPY --from=build /out/traefik-cloudflare-dns /traefik-cloudflare-dns
+USER nonroot:nonroot
+ENTRYPOINT ["/traefik-cloudflare-dns"]

LICENSE

@@ -0,0 +1,201 @@
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README.md

@@ -0,0 +1,95 @@
+# traefik-cloudflare-dns
+
+**Cloudflare DNS records that follow your Traefik containers.** traefik-cloudflare-dns watches Docker for containers whose Traefik router rules name a host, creates a Cloudflare record for each new host, and deletes the records it created once their host has been gone long enough.
+
+- **Follows Docker events.** It reacts when a container starts, stops or is removed, and resyncs every minute in case an event was missed.
+- **Never touches records it didn't make.** It only treats a record as its own when the record points at this instance's `TARGET` and carries its comment and tags. Records made by hand, or by another instance pointing at another server, stay as they are.
+- **Waits before deleting.** A host must be down for `DELETE_AFTER` (1 hour by default) before its record is removed, so redeploys and restarts never cause a DNS gap.
+- **Small and safe.** A static, distroless, non-root image with no ports, built to sit behind a read-only Docker socket proxy.
+
+## How it decides what to create
+
+Every running container's `traefik.http.routers.<name>.rule` labels are read. Each hostname in a `Host(...)` matcher that is `DOMAIN` or a name under it gets a record:
+
+| `TARGET` | Record |
+| --- | --- |
+| IPv4 address | `A` |
+| IPv6 address | `AAAA` |
+| hostname | `CNAME` |
+
+If a record with that name already exists and isn't owned by this instance, it is left alone, and a warning is logged once.
+
+A typical setup is one wildcard record (`*.example.com`) for your main server, plus one instance of this tool on every other server, with `TARGET` set to that server's IP. Explicit records take priority over the wildcard, so each app's name resolves to the server it runs on.
+
+## Quick start
+
+```yaml
+services:
+  traefik-cloudflare-dns:
+    image: ghcr.io/tiennm99/traefik-cloudflare-dns:1
+    restart: unless-stopped
+    environment:
+      CF_API_TOKEN: ${CF_API_TOKEN:?required}
+      CF_ZONE_ID: ${CF_ZONE_ID:?required}
+      DOMAIN: example.com
+      TARGET: 192.0.2.10
+      DOCKER_HOST: tcp://dockerproxy:2375
+    depends_on:
+      - dockerproxy
+
+  dockerproxy:
+    image: tecnativa/docker-socket-proxy:latest
+    restart: unless-stopped
+    environment:
+      CONTAINERS: 1
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock:ro
+```
+
+The proxy only needs `CONTAINERS`. Events and ping are allowed by the proxy's defaults, and every `POST` is refused, so the tool can read Docker but never change it.
+
+Create the Cloudflare API token with **Zone → DNS → Edit**, limited to the one zone.
+
+## Configuration
+
+| Variable | Default | Purpose |
+| --- | --- | --- |
+| `CF_API_TOKEN` | required | Cloudflare API token with DNS edit on the zone |
+| `CF_ZONE_ID` | required | Zone ID, from the zone's overview page |
+| `DOMAIN` | required | Only hosts equal to or under this name are managed |
+| `TARGET` | required | Record content: this server's IP, or a hostname for a CNAME |
+| `PROXIED` | `false` | Create orange-cloud (proxied) records |
+| `TTL` | `1` | Record TTL in seconds; `1` means automatic |
+| `RECORD_COMMENT` | `managed by traefik-cloudflare-dns` | Comment set on every record, and part of ownership |
+| `RECORD_TAGS` | empty | Comma-separated `name:value` tags, set on every record and part of ownership |
+| `DELETE_AFTER` | `1h` | How long a host must be down before its record is deleted |
+| `RESYNC_INTERVAL` | `1m` | Full resync period, on top of Docker events |
+| `DRY_RUN` | `false` | Log creates and deletes without making them |
+| `DOCKER_HOST` | `unix:///var/run/docker.sock` | Docker API endpoint, `unix://` or `tcp://` |
+| `LOG_LEVEL` | `info` | `debug`, `info`, `warn` or `error` |
+
+### Comments and tags
+
+Cloudflare allows record comments on every plan. They are limited to 100 characters on Free and 500 on paid plans. **Tags are only available on paid plans**, and on a Free zone Cloudflare rejects any record that has them, so leave `RECORD_TAGS` empty there.
+
+Ownership is matched exactly. If you change `RECORD_COMMENT` or `RECORD_TAGS`, records created under the old values are no longer this instance's, so they won't be deleted automatically. Update or remove them by hand.
+
+### Deletion timing
+
+The clock for `DELETE_AFTER` starts when a resync finds an owned record whose host no longer belongs to any running container. It resets if the host comes back. The timers live in memory, so a restart starts them over. That can only delay a deletion, never bring one forward.
+
+Give each server's instance its own `TARGET`. Two instances pointing at the same target with the same comment would each treat the other's records as their own.
+
+## Development
+
+```bash
+go vet ./...
+go test -race ./...
+docker build -t traefik-cloudflare-dns:dev .
+```
+
+CI runs the same checks on every push. Pushes to `main` publish `ghcr.io/tiennm99/traefik-cloudflare-dns:edge`. A `vX.Y.Z` tag publishes `X.Y.Z`, `X.Y` and `X`.
+
+## License
+
+[Apache 2.0](LICENSE)

client_test.go

@@ -0,0 +1,122 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestCloudflareClientPaginatesAndFilters(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Header.Get("Authorization") != "Bearer tok" {
+			t.Errorf("missing token")
+		}
+		page := r.URL.Query().Get("page")
+		results := map[string]string{
+			"1": `[{"id":"1","type":"A","name":"a.example.com","content":"192.0.2.1"},{"id":"2","type":"TXT","name":"t.example.com","content":"x"}]`,
+			"2": `[{"id":"3","type":"CNAME","name":"c.example.com","content":"h.example.net","comment":"managed"}]`,
+		}[page]
+		fmt.Fprintf(w, `{"success":true,"errors":[],"result":%s,"result_info":{"page":%s,"total_pages":2}}`, results, page)
+	}))
+	defer srv.Close()
+
+	c := NewCloudflareClient("tok", "zone")
+	c.base = srv.URL
+	records, err := c.ListRecords(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(records) != 2 || records[1].Comment != "managed" {
+		t.Fatalf("records = %+v", records)
+	}
+}
+
+func TestCloudflareClientCreateSendsCommentAndTags(t *testing.T) {
+	var got Record
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost || r.URL.Path != "/zones/zone/dns_records" {
+			t.Errorf("unexpected %s %s", r.Method, r.URL.Path)
+		}
+		_ = json.NewDecoder(r.Body).Decode(&got)
+		got.ID = "new"
+		b, _ := json.Marshal(got)
+		fmt.Fprintf(w, `{"success":true,"errors":[],"result":%s}`, b)
+	}))
+	defer srv.Close()
+
+	c := NewCloudflareClient("tok", "zone")
+	c.base = srv.URL
+	rec, err := c.CreateRecord(context.Background(), Record{
+		Type: "A", Name: "a.example.com", Content: "192.0.2.1", TTL: 1,
+		Comment: "managed by traefik-cloudflare-dns", Tags: []string{"owner:x"},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if rec.ID != "new" || got.Comment != "managed by traefik-cloudflare-dns" || len(got.Tags) != 1 {
+		t.Fatalf("sent %+v, got %+v", got, rec)
+	}
+}
+
+func TestCloudflareClientReportsAPIErrors(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusForbidden)
+		fmt.Fprint(w, `{"success":false,"errors":[{"code":10000,"message":"Authentication error"}],"result":null}`)
+	}))
+	defer srv.Close()
+
+	c := NewCloudflareClient("tok", "zone")
+	c.base = srv.URL
+	_, err := c.ListRecords(context.Background())
+	if err == nil || !strings.Contains(err.Error(), "10000 Authentication error") {
+		t.Fatalf("err = %v", err)
+	}
+}
+
+func TestDockerClientListsAndStreamsEvents(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch r.URL.Path {
+		case "/containers/json":
+			fmt.Fprint(w, `[{"Id":"abc","Labels":{"traefik.http.routers.r.rule":"Host(`+"`a.example.com`"+`)"}}]`)
+		case "/events":
+			if !strings.Contains(r.URL.Query().Get("filters"), `"start"`) {
+				t.Errorf("filters = %s", r.URL.Query().Get("filters"))
+			}
+			fmt.Fprint(w, `{"Type":"container","Action":"start"}`+"\n"+`{"Type":"container","Action":"die"}`+"\n")
+		default:
+			http.NotFound(w, r)
+		}
+	}))
+	defer srv.Close()
+
+	d, err := NewDockerClient("tcp://" + strings.TrimPrefix(srv.URL, "http://"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	containers, err := d.RunningContainers(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(containers) != 1 || HostsFromLabels(containers[0].Labels)[0] != "a.example.com" {
+		t.Fatalf("containers = %+v", containers)
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	var actions []string
+	_ = d.WatchContainerEvents(ctx, func(a string) { actions = append(actions, a) })
+	if strings.Join(actions, ",") != "start,die" {
+		t.Fatalf("actions = %v", actions)
+	}
+}
+
+func TestNewDockerClientRejectsUnknownScheme(t *testing.T) {
+	if _, err := NewDockerClient("ssh://host"); err == nil {
+		t.Fatal("expected an error")
+	}
+}

cloudflare.go

@@ -0,0 +1,137 @@
+package main
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+)
+
+const cloudflareAPI = "https://api.cloudflare.com/client/v4"
+
+// Record is a Cloudflare DNS record, limited to the fields this tool uses.
+type Record struct {
+	ID      string   `json:"id,omitempty"`
+	Type    string   `json:"type"`
+	Name    string   `json:"name"`
+	Content string   `json:"content"`
+	TTL     int      `json:"ttl,omitempty"`
+	Proxied bool     `json:"proxied"`
+	Comment string   `json:"comment,omitempty"`
+	Tags    []string `json:"tags,omitempty"`
+}
+
+// CloudflareClient manages DNS records in one zone with a scoped API token.
+type CloudflareClient struct {
+	base   string
+	token  string
+	zoneID string
+	http   *http.Client
+}
+
+// NewCloudflareClient returns a client for zoneID.
+func NewCloudflareClient(token, zoneID string) *CloudflareClient {
+	return &CloudflareClient{
+		base:   cloudflareAPI,
+		token:  token,
+		zoneID: zoneID,
+		http:   &http.Client{Timeout: 30 * time.Second},
+	}
+}
+
+type cfResponse struct {
+	Success bool `json:"success"`
+	Errors  []struct {
+		Code    int    `json:"code"`
+		Message string `json:"message"`
+	} `json:"errors"`
+	Result     json.RawMessage `json:"result"`
+	ResultInfo struct {
+		Page       int `json:"page"`
+		TotalPages int `json:"total_pages"`
+	} `json:"result_info"`
+}
+
+func (c *CloudflareClient) do(ctx context.Context, method, path string, body any) (*cfResponse, error) {
+	var reader io.Reader
+	if body != nil {
+		b, err := json.Marshal(body)
+		if err != nil {
+			return nil, err
+		}
+		reader = bytes.NewReader(b)
+	}
+	req, err := http.NewRequestWithContext(ctx, method, c.base+path, reader)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Authorization", "Bearer "+c.token)
+	req.Header.Set("Content-Type", "application/json")
+	resp, err := c.http.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	var out cfResponse
+	if err := json.NewDecoder(io.LimitReader(resp.Body, 32<<20)).Decode(&out); err != nil {
+		return nil, fmt.Errorf("HTTP %d: undecodable response: %w", resp.StatusCode, err)
+	}
+	if !out.Success {
+		var msgs []string
+		for _, e := range out.Errors {
+			msgs = append(msgs, fmt.Sprintf("%d %s", e.Code, e.Message))
+		}
+		return nil, fmt.Errorf("HTTP %d: %s", resp.StatusCode, strings.Join(msgs, "; "))
+	}
+	return &out, nil
+}
+
+// ListRecords returns every A, AAAA and CNAME record in the zone.
+func (c *CloudflareClient) ListRecords(ctx context.Context) ([]Record, error) {
+	var all []Record
+	for page := 1; ; page++ {
+		q := url.Values{"per_page": {"100"}, "page": {fmt.Sprint(page)}}
+		out, err := c.do(ctx, http.MethodGet, "/zones/"+c.zoneID+"/dns_records?"+q.Encode(), nil)
+		if err != nil {
+			return nil, fmt.Errorf("list records: %w", err)
+		}
+		var records []Record
+		if err := json.Unmarshal(out.Result, &records); err != nil {
+			return nil, fmt.Errorf("list records: %w", err)
+		}
+		for _, r := range records {
+			if r.Type == "A" || r.Type == "AAAA" || r.Type == "CNAME" {
+				all = append(all, r)
+			}
+		}
+		if out.ResultInfo.TotalPages <= page {
+			return all, nil
+		}
+	}
+}
+
+// CreateRecord creates r and returns the stored record.
+func (c *CloudflareClient) CreateRecord(ctx context.Context, r Record) (Record, error) {
+	out, err := c.do(ctx, http.MethodPost, "/zones/"+c.zoneID+"/dns_records", r)
+	if err != nil {
+		return Record{}, fmt.Errorf("create %s: %w", r.Name, err)
+	}
+	var created Record
+	if err := json.Unmarshal(out.Result, &created); err != nil {
+		return Record{}, fmt.Errorf("create %s: %w", r.Name, err)
+	}
+	return created, nil
+}
+
+// DeleteRecord deletes the record with id.
+func (c *CloudflareClient) DeleteRecord(ctx context.Context, id string) error {
+	if _, err := c.do(ctx, http.MethodDelete, "/zones/"+c.zoneID+"/dns_records/"+id, nil); err != nil {
+		return fmt.Errorf("delete %s: %w", id, err)
+	}
+	return nil
+}

config.go

@@ -0,0 +1,163 @@
+package main
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"slices"
+	"strconv"
+	"strings"
+	"time"
+)
+
+const defaultComment = "managed by traefik-cloudflare-dns"
+
+// Config holds every setting, read from environment variables.
+type Config struct {
+	APIToken       string
+	ZoneID         string
+	Domain         string
+	Target         string
+	RecordType     string
+	Proxied        bool
+	TTL            int
+	Comment        string
+	Tags           []string
+	DeleteAfter    time.Duration
+	ResyncInterval time.Duration
+	DryRun         bool
+	DockerHost     string
+	LogLevel       string
+}
+
+// LoadConfig reads the configuration through getenv and validates it.
+func LoadConfig(getenv func(string) string) (Config, error) {
+	c := Config{
+		APIToken:   strings.TrimSpace(getenv("CF_API_TOKEN")),
+		ZoneID:     strings.TrimSpace(getenv("CF_ZONE_ID")),
+		Domain:     strings.ToLower(strings.Trim(strings.TrimSpace(getenv("DOMAIN")), ".")),
+		Target:     strings.TrimSpace(getenv("TARGET")),
+		Comment:    getenv("RECORD_COMMENT"),
+		DockerHost: strings.TrimSpace(getenv("DOCKER_HOST")),
+		LogLevel:   strings.ToLower(strings.TrimSpace(getenv("LOG_LEVEL"))),
+	}
+
+	var missing []string
+	for name, value := range map[string]string{
+		"CF_API_TOKEN": c.APIToken,
+		"CF_ZONE_ID":   c.ZoneID,
+		"DOMAIN":       c.Domain,
+		"TARGET":       c.Target,
+	} {
+		if value == "" {
+			missing = append(missing, name)
+		}
+	}
+	if len(missing) > 0 {
+		slices.Sort(missing)
+		return Config{}, fmt.Errorf("missing required variables: %s", strings.Join(missing, ", "))
+	}
+
+	c.RecordType = recordTypeFor(c.Target)
+	if c.RecordType == "CNAME" {
+		c.Target = strings.ToLower(strings.TrimSuffix(c.Target, "."))
+	}
+
+	if c.Comment == "" {
+		c.Comment = defaultComment
+	}
+	if strings.ContainsAny(c.Comment, "\r\n") {
+		return Config{}, fmt.Errorf("RECORD_COMMENT must not contain line breaks")
+	}
+
+	for _, tag := range strings.Split(getenv("RECORD_TAGS"), ",") {
+		tag = strings.TrimSpace(tag)
+		if tag == "" {
+			continue
+		}
+		if !strings.Contains(tag, ":") {
+			return Config{}, fmt.Errorf("RECORD_TAGS entry %q is not in name:value form", tag)
+		}
+		c.Tags = append(c.Tags, tag)
+	}
+
+	var err error
+	if c.Proxied, err = parseBool(getenv, "PROXIED", false); err != nil {
+		return Config{}, err
+	}
+	if c.DryRun, err = parseBool(getenv, "DRY_RUN", false); err != nil {
+		return Config{}, err
+	}
+	if c.TTL, err = parseInt(getenv, "TTL", 1); err != nil {
+		return Config{}, err
+	}
+	if c.DeleteAfter, err = parseDuration(getenv, "DELETE_AFTER", time.Hour); err != nil {
+		return Config{}, err
+	}
+	if c.ResyncInterval, err = parseDuration(getenv, "RESYNC_INTERVAL", time.Minute); err != nil {
+		return Config{}, err
+	}
+	if c.ResyncInterval <= 0 {
+		return Config{}, fmt.Errorf("RESYNC_INTERVAL must be positive")
+	}
+
+	if c.DockerHost == "" {
+		c.DockerHost = "unix:///var/run/docker.sock"
+	}
+	if c.LogLevel == "" {
+		c.LogLevel = "info"
+	}
+	return c, nil
+}
+
+// recordTypeFor returns A or AAAA for an IP target and CNAME for a hostname.
+func recordTypeFor(target string) string {
+	ip := net.ParseIP(target)
+	switch {
+	case ip == nil:
+		return "CNAME"
+	case ip.To4() != nil:
+		return "A"
+	default:
+		return "AAAA"
+	}
+}
+
+func parseBool(getenv func(string) string, name string, def bool) (bool, error) {
+	v := strings.TrimSpace(getenv(name))
+	if v == "" {
+		return def, nil
+	}
+	b, err := strconv.ParseBool(v)
+	if err != nil {
+		return false, fmt.Errorf("%s: %q is not a boolean", name, v)
+	}
+	return b, nil
+}
+
+func parseInt(getenv func(string) string, name string, def int) (int, error) {
+	v := strings.TrimSpace(getenv(name))
+	if v == "" {
+		return def, nil
+	}
+	n, err := strconv.Atoi(v)
+	if err != nil {
+		return 0, fmt.Errorf("%s: %q is not an integer", name, v)
+	}
+	return n, nil
+}
+
+func parseDuration(getenv func(string) string, name string, def time.Duration) (time.Duration, error) {
+	v := strings.TrimSpace(getenv(name))
+	if v == "" {
+		return def, nil
+	}
+	d, err := time.ParseDuration(v)
+	if err != nil || d < 0 {
+		return 0, fmt.Errorf("%s: %q is not a non-negative duration such as 1h or 30m", name, v)
+	}
+	return d, nil
+}
+
+// osGetenv is the production getenv.
+var osGetenv = os.Getenv

config_test.go

@@ -0,0 +1,99 @@
+package main
+
+import (
+	"strings"
+	"testing"
+	"time"
+)
+
+func envOf(m map[string]string) func(string) string {
+	return func(k string) string { return m[k] }
+}
+
+func requiredEnv() map[string]string {
+	return map[string]string{
+		"CF_API_TOKEN": "token",
+		"CF_ZONE_ID":   "zone",
+		"DOMAIN":       "Example.com.",
+		"TARGET":       "192.0.2.10",
+	}
+}
+
+func TestLoadConfigDefaults(t *testing.T) {
+	c, err := LoadConfig(envOf(requiredEnv()))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if c.Domain != "example.com" || c.RecordType != "A" || c.TTL != 1 || c.Proxied || c.DryRun {
+		t.Fatalf("unexpected config: %+v", c)
+	}
+	if c.Comment != "managed by traefik-cloudflare-dns" {
+		t.Fatalf("comment = %q", c.Comment)
+	}
+	if c.DeleteAfter != time.Hour || c.ResyncInterval != time.Minute {
+		t.Fatalf("durations = %v, %v", c.DeleteAfter, c.ResyncInterval)
+	}
+	if c.DockerHost != "unix:///var/run/docker.sock" {
+		t.Fatalf("docker host = %q", c.DockerHost)
+	}
+}
+
+func TestLoadConfigMissing(t *testing.T) {
+	_, err := LoadConfig(envOf(map[string]string{"DOMAIN": "example.com"}))
+	if err == nil || !strings.Contains(err.Error(), "CF_API_TOKEN, CF_ZONE_ID, TARGET") {
+		t.Fatalf("err = %v", err)
+	}
+}
+
+func TestLoadConfigRecordType(t *testing.T) {
+	for target, want := range map[string]string{
+		"192.0.2.10":        "A",
+		"2001:db8::1":       "AAAA",
+		"Host.Example.net.": "CNAME",
+	} {
+		env := requiredEnv()
+		env["TARGET"] = target
+		c, err := LoadConfig(envOf(env))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if c.RecordType != want {
+			t.Errorf("TARGET %q: type %s, want %s", target, c.RecordType, want)
+		}
+	}
+}
+
+func TestLoadConfigOptional(t *testing.T) {
+	env := requiredEnv()
+	env["RECORD_COMMENT"] = "created by the jp companion"
+	env["RECORD_TAGS"] = "managed-by:traefik-cloudflare-dns, server:jp"
+	env["PROXIED"] = "true"
+	env["DELETE_AFTER"] = "30m"
+	env["DRY_RUN"] = "1"
+	c, err := LoadConfig(envOf(env))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if c.Comment != "created by the jp companion" || !c.Proxied || !c.DryRun || c.DeleteAfter != 30*time.Minute {
+		t.Fatalf("unexpected config: %+v", c)
+	}
+	if len(c.Tags) != 2 || c.Tags[1] != "server:jp" {
+		t.Fatalf("tags = %v", c.Tags)
+	}
+}
+
+func TestLoadConfigInvalid(t *testing.T) {
+	for name, kv := range map[string][2]string{
+		"bad tag":      {"RECORD_TAGS", "nocolon"},
+		"bad bool":     {"PROXIED", "maybe"},
+		"bad duration": {"DELETE_AFTER", "soon"},
+		"line break":   {"RECORD_COMMENT", "a\nb"},
+		"zero resync":  {"RESYNC_INTERVAL", "0s"},
+	} {
+		env := requiredEnv()
+		env[kv[0]] = kv[1]
+		if _, err := LoadConfig(envOf(env)); err == nil {
+			t.Errorf("%s: expected an error", name)
+		}
+	}
+}

docker.go

@@ -0,0 +1,115 @@
+package main
+
+import (
+	"bufio"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+)
+
+// Container is the part of a running container this tool reads.
+type Container struct {
+	ID     string            `json:"Id"`
+	Labels map[string]string `json:"Labels"`
+}
+
+// DockerClient talks to the Docker Engine API over a unix socket or TCP,
+// such as a read-only docker-socket-proxy.
+type DockerClient struct {
+	base   string
+	http   *http.Client
+	stream *http.Client
+}
+
+// NewDockerClient builds a client from a DOCKER_HOST value
+// (unix:///path or tcp://host:port).
+func NewDockerClient(dockerHost string) (*DockerClient, error) {
+	u, err := url.Parse(dockerHost)
+	if err != nil {
+		return nil, fmt.Errorf("DOCKER_HOST %q: %w", dockerHost, err)
+	}
+	transport := &http.Transport{}
+	base := ""
+	switch u.Scheme {
+	case "unix":
+		socket := u.Path
+		transport.DialContext = func(ctx context.Context, _, _ string) (net.Conn, error) {
+			var d net.Dialer
+			return d.DialContext(ctx, "unix", socket)
+		}
+		base = "http://docker"
+	case "tcp", "http":
+		base = "http://" + u.Host
+	default:
+		return nil, fmt.Errorf("DOCKER_HOST %q: scheme must be unix or tcp", dockerHost)
+	}
+	return &DockerClient{
+		base:   base,
+		http:   &http.Client{Transport: transport, Timeout: 30 * time.Second},
+		stream: &http.Client{Transport: transport},
+	}, nil
+}
+
+// RunningContainers lists running containers with their labels.
+func (d *DockerClient) RunningContainers(ctx context.Context) ([]Container, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, d.base+"/containers/json", nil)
+	if err != nil {
+		return nil, err
+	}
+	resp, err := d.http.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("list containers: %w", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(io.LimitReader(resp.Body, 512))
+		return nil, fmt.Errorf("list containers: HTTP %d: %s", resp.StatusCode, strings.TrimSpace(string(body)))
+	}
+	var containers []Container
+	if err := json.NewDecoder(resp.Body).Decode(&containers); err != nil {
+		return nil, fmt.Errorf("list containers: %w", err)
+	}
+	return containers, nil
+}
+
+// WatchContainerEvents streams container start, die and destroy events and
+// calls onEvent for each one. It returns when the stream ends or ctx is done.
+func (d *DockerClient) WatchContainerEvents(ctx context.Context, onEvent func(action string)) error {
+	filters := `{"type":["container"],"event":["start","die","destroy"]}`
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet,
+		d.base+"/events?filters="+url.QueryEscape(filters), nil)
+	if err != nil {
+		return err
+	}
+	resp, err := d.stream.Do(req)
+	if err != nil {
+		return fmt.Errorf("watch events: %w", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(io.LimitReader(resp.Body, 512))
+		return fmt.Errorf("watch events: HTTP %d: %s", resp.StatusCode, strings.TrimSpace(string(body)))
+	}
+	dec := json.NewDecoder(bufio.NewReader(resp.Body))
+	for {
+		var ev struct {
+			Type   string `json:"Type"`
+			Action string `json:"Action"`
+		}
+		if err := dec.Decode(&ev); err != nil {
+			if ctx.Err() != nil {
+				return ctx.Err()
+			}
+			return fmt.Errorf("watch events: %w", err)
+		}
+		if ev.Type == "container" {
+			onEvent(ev.Action)
+		}
+	}
+}

go.mod

@@ -0,0 +1,3 @@
+module github.com/tiennm99/traefik-cloudflare-dns
+
+go 1.27.1

hosts.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"regexp"
+	"strings"
+)
+
+var (
+	routerRuleLabel = regexp.MustCompile(`^traefik\.http\.routers\.[^.]+\.rule$`)
+	hostMatcher     = regexp.MustCompile(`Host\(([^)]*)\)`)
+	backtickValue   = regexp.MustCompile("`([^`]+)`")
+)
+
+// HostsFromLabels returns the hostnames that a container's Traefik HTTP
+// router rules match with Host(...), lowercased and deduplicated.
+// HostRegexp and other matchers are ignored. A container labelled
+// traefik.enable=false yields nothing.
+func HostsFromLabels(labels map[string]string) []string {
+	if strings.EqualFold(strings.TrimSpace(labels["traefik.enable"]), "false") {
+		return nil
+	}
+	seen := map[string]bool{}
+	var hosts []string
+	for key, rule := range labels {
+		if !routerRuleLabel.MatchString(key) {
+			continue
+		}
+		for _, m := range hostMatcher.FindAllStringSubmatch(rule, -1) {
+			for _, v := range backtickValue.FindAllStringSubmatch(m[1], -1) {
+				host := strings.ToLower(strings.TrimSuffix(strings.TrimSpace(v[1]), "."))
+				if host != "" && !seen[host] {
+					seen[host] = true
+					hosts = append(hosts, host)
+				}
+			}
+		}
+	}
+	return hosts
+}
+
+// InDomain reports whether host is domain itself or a name under it.
+func InDomain(host, domain string) bool {
+	return host == domain || strings.HasSuffix(host, "."+domain)
+}

hosts_test.go

@@ -0,0 +1,71 @@
+package main
+
+import (
+	"slices"
+	"testing"
+)
+
+func TestHostsFromLabels(t *testing.T) {
+	tests := []struct {
+		name   string
+		labels map[string]string
+		want   []string
+	}{
+		{
+			name: "coolify rule with path prefix",
+			labels: map[string]string{
+				"traefik.enable":                       "true",
+				"traefik.http.routers.https-0-x.rule":  "Host(`App.Example.com`) && PathPrefix(`/`)",
+				"traefik.http.routers.http-0-x.rule":   "Host(`app.example.com`) && PathPrefix(`/`)",
+				"traefik.http.services.x.loadbalancer": "ignored",
+			},
+			want: []string{"app.example.com"},
+		},
+		{
+			name: "several hosts in one matcher and several matchers",
+			labels: map[string]string{
+				"traefik.http.routers.r.rule": "Host(`a.example.com`, `b.example.com`) || Host(`c.example.com.`)",
+			},
+			want: []string{"a.example.com", "b.example.com", "c.example.com"},
+		},
+		{
+			name: "host regexp and tcp routers are ignored",
+			labels: map[string]string{
+				"traefik.http.routers.r.rule": "HostRegexp(`{sub:[a-z]+}.example.com`)",
+				"traefik.tcp.routers.t.rule":  "HostSNI(`db.example.com`)",
+			},
+			want: nil,
+		},
+		{
+			name: "traefik disabled",
+			labels: map[string]string{
+				"traefik.enable":              "false",
+				"traefik.http.routers.r.rule": "Host(`a.example.com`)",
+			},
+			want: nil,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := HostsFromLabels(tt.labels)
+			slices.Sort(got)
+			if !slices.Equal(got, tt.want) {
+				t.Fatalf("got %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestInDomain(t *testing.T) {
+	for host, want := range map[string]bool{
+		"example.com":          true,
+		"app.example.com":      true,
+		"a.b.example.com":      true,
+		"notexample.com":       false,
+		"example.com.evil.net": false,
+	} {
+		if got := InDomain(host, "example.com"); got != want {
+			t.Errorf("InDomain(%q) = %v, want %v", host, got, want)
+		}
+	}
+}

main.go

@@ -0,0 +1,123 @@
+// Command traefik-cloudflare-dns creates Cloudflare DNS records for the
+// hostnames in Traefik router labels of running Docker containers, and
+// deletes the records it created once their host has been down long enough.
+package main
+
+import (
+	"context"
+	"log/slog"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+)
+
+const (
+	debounce   = 2 * time.Second
+	retryAfter = 10 * time.Second
+)
+
+func main() {
+	cfg, err := LoadConfig(osGetenv)
+	if err != nil {
+		slog.Error("invalid configuration", "err", err)
+		os.Exit(2)
+	}
+	log := slog.New(slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{Level: parseLevel(cfg.LogLevel)}))
+
+	docker, err := NewDockerClient(cfg.DockerHost)
+	if err != nil {
+		log.Error("invalid configuration", "err", err)
+		os.Exit(2)
+	}
+	rec := NewReconciler(cfg, NewCloudflareClient(cfg.APIToken, cfg.ZoneID), docker, log)
+
+	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
+	defer stop()
+
+	log.Info("starting",
+		"domain", cfg.Domain, "target", cfg.Target, "type", cfg.RecordType,
+		"proxied", cfg.Proxied, "comment", cfg.Comment, "tags", cfg.Tags,
+		"delete_after", cfg.DeleteAfter, "resync_interval", cfg.ResyncInterval,
+		"dry_run", cfg.DryRun, "docker_host", cfg.DockerHost)
+
+	trigger := make(chan struct{}, 1)
+	go watchEvents(ctx, docker, trigger, log)
+	run(ctx, rec, trigger, cfg.ResyncInterval, log)
+	log.Info("stopped")
+}
+
+// run reconciles once at start, then after each burst of container events,
+// on every resync tick, and shortly after a failed pass, until ctx is done.
+func run(ctx context.Context, rec *Reconciler, trigger <-chan struct{}, every time.Duration, log *slog.Logger) {
+	var retry <-chan time.Time
+	pass := func() {
+		retry = nil
+		if err := rec.Reconcile(ctx); err != nil && ctx.Err() == nil {
+			log.Error("reconcile failed; retrying", "err", err, "in", retryAfter)
+			retry = time.After(retryAfter)
+		}
+	}
+	pass()
+	ticker := time.NewTicker(every)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			pass()
+		case <-retry:
+			pass()
+		case <-trigger:
+			select {
+			case <-ctx.Done():
+				return
+			case <-time.After(debounce):
+			}
+			pass()
+		}
+	}
+}
+
+// watchEvents keeps a Docker event stream open and signals trigger on every
+// container start, die or destroy, reconnecting with backoff when it drops.
+func watchEvents(ctx context.Context, docker *DockerClient, trigger chan<- struct{}, log *slog.Logger) {
+	backoff := time.Second
+	for ctx.Err() == nil {
+		started := time.Now()
+		err := docker.WatchContainerEvents(ctx, func(action string) {
+			log.Debug("container event", "action", action)
+			select {
+			case trigger <- struct{}{}:
+			default:
+			}
+		})
+		if ctx.Err() != nil {
+			return
+		}
+		if time.Since(started) > time.Minute {
+			backoff = time.Second
+		}
+		log.Warn("docker event stream ended; reconnecting", "err", err, "in", backoff)
+		select {
+		case <-ctx.Done():
+			return
+		case <-time.After(backoff):
+		}
+		backoff = min(backoff*2, time.Minute)
+	}
+}
+
+func parseLevel(s string) slog.Level {
+	switch s {
+	case "debug":
+		return slog.LevelDebug
+	case "warn":
+		return slog.LevelWarn
+	case "error":
+		return slog.LevelError
+	default:
+		return slog.LevelInfo
+	}
+}

reconcile.go

@@ -0,0 +1,173 @@
+package main
+
+import (
+	"context"
+	"log/slog"
+	"slices"
+	"time"
+)
+
+// DNS is the record store the reconciler writes to.
+type DNS interface {
+	ListRecords(ctx context.Context) ([]Record, error)
+	CreateRecord(ctx context.Context, r Record) (Record, error)
+	DeleteRecord(ctx context.Context, id string) error
+}
+
+// ContainerSource lists the running containers.
+type ContainerSource interface {
+	RunningContainers(ctx context.Context) ([]Container, error)
+}
+
+// Reconciler keeps the zone in line with the hosts of running containers.
+//
+// A record is owned when its content is this instance's target and it
+// carries the configured comment and every configured tag. Only owned
+// records are deleted, so records made by hand, or by another instance
+// pointing at another server, are never touched.
+type Reconciler struct {
+	cfg        Config
+	dns        DNS
+	containers ContainerSource
+	log        *slog.Logger
+	now        func() time.Time
+
+	// missingSince tracks when each owned record's host was last served.
+	missingSince map[string]time.Time
+	// warned avoids repeating the same conflict warning every pass.
+	warned map[string]bool
+}
+
+// NewReconciler returns a reconciler for cfg.
+func NewReconciler(cfg Config, dns DNS, containers ContainerSource, log *slog.Logger) *Reconciler {
+	return &Reconciler{
+		cfg:          cfg,
+		dns:          dns,
+		containers:   containers,
+		log:          log,
+		now:          time.Now,
+		missingSince: map[string]time.Time{},
+		warned:       map[string]bool{},
+	}
+}
+
+func (r *Reconciler) owns(rec Record) bool {
+	if rec.Type != r.cfg.RecordType || rec.Content != r.cfg.Target || rec.Comment != r.cfg.Comment {
+		return false
+	}
+	for _, tag := range r.cfg.Tags {
+		if !slices.Contains(rec.Tags, tag) {
+			return false
+		}
+	}
+	return true
+}
+
+// Reconcile runs one pass: create records for new hosts, and delete owned
+// records whose host has been absent for at least DeleteAfter.
+func (r *Reconciler) Reconcile(ctx context.Context) error {
+	containers, err := r.containers.RunningContainers(ctx)
+	if err != nil {
+		return err
+	}
+	desired := map[string]bool{}
+	for _, c := range containers {
+		for _, h := range HostsFromLabels(c.Labels) {
+			if InDomain(h, r.cfg.Domain) {
+				desired[h] = true
+			}
+		}
+	}
+
+	records, err := r.dns.ListRecords(ctx)
+	if err != nil {
+		return err
+	}
+	byName := map[string][]Record{}
+	for _, rec := range records {
+		byName[rec.Name] = append(byName[rec.Name], rec)
+	}
+
+	for _, host := range sortedKeys(desired) {
+		existing := byName[host]
+		if slices.ContainsFunc(existing, r.owns) {
+			delete(r.missingSince, host)
+			continue
+		}
+		if len(existing) > 0 {
+			if !r.warned[host] {
+				r.log.Warn("record exists and is not managed by this instance; leaving it alone",
+					"host", host, "type", existing[0].Type, "content", existing[0].Content)
+				r.warned[host] = true
+			}
+			continue
+		}
+		rec := Record{
+			Type:    r.cfg.RecordType,
+			Name:    host,
+			Content: r.cfg.Target,
+			TTL:     r.cfg.TTL,
+			Proxied: r.cfg.Proxied,
+			Comment: r.cfg.Comment,
+			Tags:    r.cfg.Tags,
+		}
+		if r.cfg.DryRun {
+			r.log.Info("dry run: would create record", "host", host, "type", rec.Type, "content", rec.Content)
+			continue
+		}
+		if _, err := r.dns.CreateRecord(ctx, rec); err != nil {
+			r.log.Error("create record failed", "host", host, "err", err)
+			continue
+		}
+		r.log.Info("created record", "host", host, "type", rec.Type, "content", rec.Content)
+	}
+	for host := range r.warned {
+		if !desired[host] {
+			delete(r.warned, host)
+		}
+	}
+
+	now := r.now()
+	owned := map[string]bool{}
+	for _, rec := range records {
+		if !r.owns(rec) || desired[rec.Name] {
+			continue
+		}
+		owned[rec.Name] = true
+		since, tracked := r.missingSince[rec.Name]
+		if !tracked {
+			r.missingSince[rec.Name] = now
+			r.log.Info("host no longer served; record will be deleted if it stays down",
+				"host", rec.Name, "delete_after", r.cfg.DeleteAfter)
+			since = now
+		}
+		if now.Sub(since) < r.cfg.DeleteAfter {
+			continue
+		}
+		if r.cfg.DryRun {
+			r.log.Info("dry run: would delete record", "host", rec.Name, "down_for", now.Sub(since).Round(time.Second))
+			continue
+		}
+		if err := r.dns.DeleteRecord(ctx, rec.ID); err != nil {
+			r.log.Error("delete record failed", "host", rec.Name, "err", err)
+			continue
+		}
+		r.log.Info("deleted record", "host", rec.Name, "down_for", now.Sub(since).Round(time.Second))
+		delete(r.missingSince, rec.Name)
+	}
+	for host := range r.missingSince {
+		if !owned[host] {
+			delete(r.missingSince, host)
+		}
+	}
+	return nil
+}
+
+func sortedKeys(m map[string]bool) []string {
+	keys := make([]string, 0, len(m))
+	for k := range m {
+		keys = append(keys, k)
+	}
+	slices.Sort(keys)
+	return keys
+}

reconcile_test.go

@@ -0,0 +1,201 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"log/slog"
+	"testing"
+	"time"
+)
+
+type fakeDNS struct {
+	records []Record
+	nextID  int
+	created []string
+	deleted []string
+}
+
+func (f *fakeDNS) ListRecords(context.Context) ([]Record, error) {
+	return append([]Record(nil), f.records...), nil
+}
+
+func (f *fakeDNS) CreateRecord(_ context.Context, r Record) (Record, error) {
+	f.nextID++
+	r.ID = fmt.Sprint(f.nextID)
+	f.records = append(f.records, r)
+	f.created = append(f.created, r.Name)
+	return r, nil
+}
+
+func (f *fakeDNS) DeleteRecord(_ context.Context, id string) error {
+	for i, r := range f.records {
+		if r.ID == id {
+			f.records = append(f.records[:i], f.records[i+1:]...)
+			f.deleted = append(f.deleted, r.Name)
+			return nil
+		}
+	}
+	return fmt.Errorf("no record %s", id)
+}
+
+type fakeContainers struct{ hosts []string }
+
+func (f *fakeContainers) RunningContainers(context.Context) ([]Container, error) {
+	var out []Container
+	for i, h := range f.hosts {
+		out = append(out, Container{
+			ID:     fmt.Sprint(i),
+			Labels: map[string]string{"traefik.http.routers.r.rule": "Host(`" + h + "`)"},
+		})
+	}
+	return out, nil
+}
+
+func newTestReconciler(t *testing.T, cfg Config, dns *fakeDNS, c *fakeContainers) (*Reconciler, *time.Time) {
+	t.Helper()
+	now := time.Date(2026, 10, 11, 0, 0, 0, 0, time.UTC)
+	r := NewReconciler(cfg, dns, c, slog.New(slog.NewTextHandler(io.Discard, nil)))
+	r.now = func() time.Time { return now }
+	return r, &now
+}
+
+func testConfig() Config {
+	return Config{
+		Domain:      "example.com",
+		Target:      "192.0.2.10",
+		RecordType:  "A",
+		TTL:         1,
+		Comment:     defaultComment,
+		DeleteAfter: time.Hour,
+	}
+}
+
+func TestReconcileCreatesOnlyHostsInDomain(t *testing.T) {
+	dns := &fakeDNS{}
+	r, _ := newTestReconciler(t, testConfig(), dns, &fakeContainers{hosts: []string{"app.example.com", "other.example.net"}})
+	if err := r.Reconcile(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	if len(dns.created) != 1 || dns.created[0] != "app.example.com" {
+		t.Fatalf("created = %v", dns.created)
+	}
+	got := dns.records[0]
+	if got.Type != "A" || got.Content != "192.0.2.10" || got.Comment != defaultComment {
+		t.Fatalf("record = %+v", got)
+	}
+	if err := r.Reconcile(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	if len(dns.created) != 1 {
+		t.Fatalf("second pass created again: %v", dns.created)
+	}
+}
+
+func TestReconcileLeavesForeignRecords(t *testing.T) {
+	dns := &fakeDNS{records: []Record{
+		{ID: "a", Type: "A", Name: "manual.example.com", Content: "192.0.2.99"},
+		{ID: "b", Type: "A", Name: "other-server.example.com", Content: "192.0.2.20", Comment: defaultComment},
+		{ID: "c", Type: "A", Name: "same-ip-no-comment.example.com", Content: "192.0.2.10"},
+	}}
+	r, now := newTestReconciler(t, testConfig(), dns, &fakeContainers{hosts: []string{"manual.example.com"}})
+	for range 3 {
+		if err := r.Reconcile(context.Background()); err != nil {
+			t.Fatal(err)
+		}
+		*now = now.Add(2 * time.Hour)
+	}
+	if len(dns.created) != 0 || len(dns.deleted) != 0 {
+		t.Fatalf("created %v, deleted %v", dns.created, dns.deleted)
+	}
+}
+
+func TestReconcileDeletesAfterGracePeriod(t *testing.T) {
+	dns := &fakeDNS{}
+	containers := &fakeContainers{hosts: []string{"app.example.com"}}
+	r, now := newTestReconciler(t, testConfig(), dns, containers)
+	ctx := context.Background()
+	if err := r.Reconcile(ctx); err != nil {
+		t.Fatal(err)
+	}
+
+	containers.hosts = nil
+	for _, step := range []time.Duration{0, 30 * time.Minute, 29 * time.Minute} {
+		*now = now.Add(step)
+		if err := r.Reconcile(ctx); err != nil {
+			t.Fatal(err)
+		}
+	}
+	if len(dns.deleted) != 0 {
+		t.Fatalf("deleted before the grace period: %v", dns.deleted)
+	}
+
+	*now = now.Add(time.Minute)
+	if err := r.Reconcile(ctx); err != nil {
+		t.Fatal(err)
+	}
+	if len(dns.deleted) != 1 || dns.deleted[0] != "app.example.com" {
+		t.Fatalf("deleted = %v", dns.deleted)
+	}
+}
+
+func TestReconcileComebackResetsGracePeriod(t *testing.T) {
+	dns := &fakeDNS{}
+	containers := &fakeContainers{hosts: []string{"app.example.com"}}
+	r, now := newTestReconciler(t, testConfig(), dns, containers)
+	ctx := context.Background()
+	steps := []struct {
+		hosts []string
+		after time.Duration
+	}{
+		{[]string{"app.example.com"}, 0},
+		{nil, 0},
+		{[]string{"app.example.com"}, 50 * time.Minute},
+		{nil, time.Minute},
+		{nil, 50 * time.Minute},
+	}
+	for _, s := range steps {
+		containers.hosts = s.hosts
+		*now = now.Add(s.after)
+		if err := r.Reconcile(ctx); err != nil {
+			t.Fatal(err)
+		}
+	}
+	if len(dns.deleted) != 0 {
+		t.Fatalf("grace period was not reset by the host coming back: %v", dns.deleted)
+	}
+}
+
+func TestReconcileRequiresTagsForOwnership(t *testing.T) {
+	cfg := testConfig()
+	cfg.Tags = []string{"managed-by:traefik-cloudflare-dns"}
+	dns := &fakeDNS{records: []Record{
+		{ID: "a", Type: "A", Name: "untagged.example.com", Content: "192.0.2.10", Comment: defaultComment},
+	}}
+	r, now := newTestReconciler(t, cfg, dns, &fakeContainers{})
+	for range 2 {
+		if err := r.Reconcile(context.Background()); err != nil {
+			t.Fatal(err)
+		}
+		*now = now.Add(2 * time.Hour)
+	}
+	if len(dns.deleted) != 0 {
+		t.Fatalf("deleted a record without the configured tag: %v", dns.deleted)
+	}
+}
+
+func TestReconcileDryRunWritesNothing(t *testing.T) {
+	cfg := testConfig()
+	cfg.DryRun = true
+	cfg.DeleteAfter = 0
+	dns := &fakeDNS{records: []Record{
+		{ID: "a", Type: "A", Name: "gone.example.com", Content: "192.0.2.10", Comment: defaultComment},
+	}}
+	r, _ := newTestReconciler(t, cfg, dns, &fakeContainers{hosts: []string{"app.example.com"}})
+	if err := r.Reconcile(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	if len(dns.created) != 0 || len(dns.deleted) != 0 {
+		t.Fatalf("dry run wrote: created %v, deleted %v", dns.created, dns.deleted)
+	}
+}