a CLI to update records for fcuny.xyzHEADmain

I want a simple solution to update the records for fcuny.xyz. The host
that serves these records is a tailscale node, so I want to also query
tailscale to get the IP for that host instead of hard coding the value.

Some other information are hard coded, like the name of the project in
GCP, etc.

11 files changed, 687 insertions, 0 deletions

diff --git a/.envrc b/.envrc
new file mode 100644
index 0000000..a5dbbcb
--- /dev/null
+++ b/.envrc
@@ -0,0 +1 @@
+use flake .
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..79ddb63
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/dns-updater
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..c27fed0
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,20 @@
+Copyright (c) Franck Cuny
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..d69b7cb
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,8 @@
+BIN := dns-updater
+
+build: go.mod main.go ts.go
+	@go build -o $(BIN)
+
+.PHONY: clean
+clean:
+	@rm -f "$(BIN)"
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..4404f41
--- /dev/null
+++ b/README.md
@@ -0,0 +1,10 @@
+Utility to update the managed zone for `fcuny.xyz` in Google Cloud DNS.
+
+I use the domain `fcuny.xyz` to run a number of services on an IP provided by Tailscale. I don't want these domains to be visible on the web, but I also want to have a valid HTTPS certificate for them. By having a proper DNS I can use ACME to get the certificates, without making them available.
+
+Instead of updating the subdomains through the [console](https://console.cloud.google.com/net-services/dns/zones/fcuny-xyz/details?project=fcuny-homelab), I can now run this program.
+
+# Run
+
+To update the records, run `nix run .`.
+
diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..3cd064c
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,122 @@
+{
+  "nodes": {
+    "flake-compat": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1673956053,
+        "narHash": "sha256-4gtG9iQuiKITOjNQQeQIpoIB6b16fm+504Ch3sNKLd8=",
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "rev": "35bb57c0c8d8b62bbfd284272c928ceb64ddbde9",
+        "type": "github"
+      },
+      "original": {
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "type": "github"
+      }
+    },
+    "futils": {
+      "locked": {
+        "lastModified": 1676283394,
+        "narHash": "sha256-XX2f9c3iySLCw54rJ/CZs+ZK6IQy7GXNY4nSOyu2QG4=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "3db36a8b464d0c4532ba1c7dda728f4576d6d073",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "gitignore": {
+      "inputs": {
+        "nixpkgs": [
+          "pre-commit-hooks",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1660459072,
+        "narHash": "sha256-8DFJjXG8zqoONA1vXtgeKXy68KdJL5UaXR8NtVMUbx8=",
+        "owner": "hercules-ci",
+        "repo": "gitignore.nix",
+        "rev": "a20de23b925fd8264fd7fad6454652e142fd7f73",
+        "type": "github"
+      },
+      "original": {
+        "owner": "hercules-ci",
+        "repo": "gitignore.nix",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1678658112,
+        "narHash": "sha256-lxm4SP00RMlejIpfHSFQg074hE6cCNUHiUiTLqlsB44=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "9dfcfbd70533f1fe7721238816f7bb59cfedc5a3",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs-stable": {
+      "locked": {
+        "lastModified": 1673800717,
+        "narHash": "sha256-SFHraUqLSu5cC6IxTprex/nTsI81ZQAtDvlBvGDWfnA=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "2f9fd351ec37f5d479556cd48be4ca340da59b8f",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-22.11",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "pre-commit-hooks": {
+      "inputs": {
+        "flake-compat": "flake-compat",
+        "flake-utils": [
+          "futils"
+        ],
+        "gitignore": "gitignore",
+        "nixpkgs": [
+          "nixpkgs"
+        ],
+        "nixpkgs-stable": "nixpkgs-stable"
+      },
+      "locked": {
+        "lastModified": 1678376203,
+        "narHash": "sha256-3tyYGyC8h7fBwncLZy5nCUjTJPrHbmNwp47LlNLOHSM=",
+        "owner": "cachix",
+        "repo": "pre-commit-hooks.nix",
+        "rev": "1a20b9708962096ec2481eeb2ddca29ed747770a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "cachix",
+        "repo": "pre-commit-hooks.nix",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "futils": "futils",
+        "nixpkgs": "nixpkgs",
+        "pre-commit-hooks": "pre-commit-hooks"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 0000000..b04c5d0
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,82 @@
+{
+  description = "Go project template";
+
+  inputs = {
+    futils.url = "github:numtide/flake-utils";
+    nixpkgs.url = "github:NixOS/nixpkgs";
+    pre-commit-hooks = {
+      url = "github:cachix/pre-commit-hooks.nix";
+      inputs = {
+        flake-utils.follows = "futils";
+        nixpkgs.follows = "nixpkgs";
+      };
+    };
+  };
+
+  outputs =
+    { self
+    , futils
+    , nixpkgs
+    , pre-commit-hooks
+    }:
+    futils.lib.eachDefaultSystem
+      (system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+        };
+        pname = "dns-updater";
+        version = "0.0.1";
+        tools = with pkgs; [
+          # https://github.com/golang/vscode-go/blob/master/docs/tools.md
+          delve
+          golangci-lint
+          gopls
+        ];
+      in
+      rec {
+        # `nix build`
+        packages."${pname}" = pkgs.buildGoModule {
+          inherit pname version;
+          src = ./.;
+          vendorSha256 = "sha256-2X3gXTdsyYOxI4vTlIllBno+XTHt3kS9hiSe2U1Tq9o=";
+        };
+        defaultPackage = packages."${pname}";
+
+        # `nix run`
+        apps = {
+          "${pname}" = futils.lib.mkApp {
+            drv = packages."${pname}";
+          };
+          default = apps."${pname}";
+        };
+
+        # `nix develop`
+        checks = {
+          pre-commit = pre-commit-hooks.lib.${system}.run {
+            src = ./.;
+            hooks = {
+              nixpkgs-fmt.enable = true;
+              yamllint.enable = true;
+              govet.enable = true;
+              gotest.enable = true;
+              gofmt.enable = true;
+              staticcheck.enable = true;
+            };
+            settings = {
+              yamllint.relaxed = true;
+            };
+          };
+        };
+
+        devShell = pkgs.mkShell {
+          buildInputs = with pkgs; [ go ] ++ tools;
+          inherit (self.checks.${system}.pre-commit) shellHook;
+        };
+      })
+    // {
+      overlay = final: prev: {
+        XXX = self.defaultPackage.${prev.system};
+      };
+    };
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..9ac77e2
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,29 @@
+module go.fcuny.net/dns-updater
+
+go 1.18
+
+require (
+	google.golang.org/api v0.112.0
+	inet.af/netaddr v0.0.0-20220811202034-502d2d690317
+)
+
+require (
+	cloud.google.com/go/compute v1.18.0 // indirect
+	cloud.google.com/go/compute/metadata v0.2.3 // indirect
+	github.com/golang/groupcache v0.0.0-20200121045136-8c9f03a8e57e // indirect
+	github.com/golang/protobuf v1.5.2 // indirect
+	github.com/google/uuid v1.3.0 // indirect
+	github.com/googleapis/enterprise-certificate-proxy v0.2.3 // indirect
+	github.com/googleapis/gax-go/v2 v2.7.0 // indirect
+	go.opencensus.io v0.24.0 // indirect
+	go4.org/intern v0.0.0-20211027215823-ae77deb06f29 // indirect
+	go4.org/unsafe/assume-no-moving-gc v0.0.0-20220617031537-928513b29760 // indirect
+	golang.org/x/net v0.8.0 // indirect
+	golang.org/x/oauth2 v0.6.0 // indirect
+	golang.org/x/sys v0.6.0 // indirect
+	golang.org/x/text v0.8.0 // indirect
+	google.golang.org/appengine v1.6.7 // indirect
+	google.golang.org/genproto v0.0.0-20230303212802-e74f57abe488 // indirect
+	google.golang.org/grpc v1.53.0 // indirect
+	google.golang.org/protobuf v1.28.1 // indirect
+)
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..1b2fd74
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,153 @@
+cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
+cloud.google.com/go v0.110.0 h1:Zc8gqp3+a9/Eyph2KDmcGaPtbKRIoqq4YTlL4NMD0Ys=
+cloud.google.com/go/compute v1.18.0 h1:FEigFqoDbys2cvFkZ9Fjq4gnHBP55anJ0yQyau2f9oY=
+cloud.google.com/go/compute v1.18.0/go.mod h1:1X7yHxec2Ga+Ss6jPyjxRxpu2uu7PLgsOVXvgU0yacs=
+cloud.google.com/go/compute/metadata v0.2.3 h1:mg4jlk7mCAj6xXp9UJ4fjI9VUI5rubuGBW5aJ7UnBMY=
+cloud.google.com/go/compute/metadata v0.2.3/go.mod h1:VAV5nSsACxMJvgaAuX6Pk2AawlZn8kiOGuCv6gTkwuA=
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diff --git a/main.go b/main.go
new file mode 100644
index 0000000..b607963
--- /dev/null
+++ b/main.go
@@ -0,0 +1,179 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"strings"
+
+	"google.golang.org/api/dns/v1"
+)
+
+const (
+	GCP_PROJECT_NAME = "fcuny-homelab"
+	GCP_MANAGED_ZONE = "fcuny-xyz"
+	TS_DEVICE_NAME   = "tahoe"
+	TTL              = 300
+)
+
+var desiredRecords = []string{
+	"bt",
+	"dash",
+	"music",
+	"unifi",
+}
+
+const usage = `Usage:
+    dns-updater [OPTIONS] <COMMAND>
+
+Options:
+    -ts-api-key    API key for tailscale
+
+Examples:
+    $ dns-updater -ts-api-key $(passage credentials/tailscale)
+    $ dns-updater -ts-api-key $(passage credentials/tailscale) update
+`
+
+var l = log.New(os.Stderr, "", 0)
+
+func main() {
+	var (
+		tsAPIKeyFlag string
+		command      string
+	)
+
+	flag.Usage = func() { fmt.Fprintf(os.Stderr, "%s\n", usage) }
+	flag.StringVar(&tsAPIKeyFlag, "ts-api-key", "", "the API key for tailscale")
+	flag.Parse()
+
+	if flag.NArg() > 1 {
+		flag.Usage()
+		os.Exit(1)
+	} else {
+		command = flag.Arg(0)
+		if command != "" && command != "update" {
+			flag.Usage()
+			os.Exit(1)
+		}
+	}
+
+	ctx := context.Background()
+
+	// we only care about IPv4 for now
+	tsIpV4Addresses, _, err := getTsIpsDevice(ctx, tsAPIKeyFlag, TS_DEVICE_NAME)
+	if err != nil {
+		l.Fatalf("failed to get the IP addresses for %s: %v", TS_DEVICE_NAME, err)
+	}
+
+	svc, err := dns.NewService(ctx)
+	if err != nil {
+		l.Fatalf("failed to create the client for Google Cloud DNS: %v", err)
+	}
+
+	zone, err := svc.ManagedZones.Get(GCP_PROJECT_NAME, GCP_MANAGED_ZONE).Context(ctx).Do()
+	if err != nil {
+		l.Fatalf("failed to get information about the managed zone %s: %+v", GCP_MANAGED_ZONE, err)
+	}
+
+	recordSets, err := svc.ResourceRecordSets.List(GCP_PROJECT_NAME, GCP_MANAGED_ZONE).Context(ctx).Do()
+	if err != nil {
+		l.Fatalf("failed to get the list of records: %+v", err)
+	}
+
+	switch command {
+	case "update":
+		updateRecords(ctx, svc, recordSets, zone, tsIpV4Addresses)
+	default:
+		listRecords(recordSets)
+	}
+}
+
+func listRecords(recordSets *dns.ResourceRecordSetsListResponse) {
+	for _, record := range recordSets.Rrsets {
+		switch record.Type {
+		case "A":
+			ips := strings.Join(record.Rrdatas[:], ",")
+			fmt.Printf("%-25s %4d %s\n", record.Name, record.Ttl, ips)
+		}
+	}
+}
+
+func updateRecords(ctx context.Context, svc *dns.Service, recordSets *dns.ResourceRecordSetsListResponse, zone *dns.ManagedZone, tsIpV4Addresses []string) {
+	var (
+		existingRecordSets = []*dns.ResourceRecordSet{}
+		recordSetsToAdd    = []*dns.ResourceRecordSet{}
+		recordSetsToDelete = []*dns.ResourceRecordSet{}
+	)
+
+	for _, record := range recordSets.Rrsets {
+		if record.Type == "A" {
+			existingRecordSets = append(existingRecordSets, record)
+		}
+	}
+
+	// first pass: create what's missing
+	for _, subdomain := range desiredRecords {
+		found := false
+		subdomain = fmt.Sprintf("%s.%s", subdomain, zone.DnsName)
+		for _, r := range existingRecordSets {
+			if subdomain == r.Name && r.Type == "A" {
+				// check that the IP addresses are correct
+				ipsFound := 0
+				for _, rr := range r.Rrdatas {
+					for _, ip := range tsIpV4Addresses {
+						if rr == ip {
+							ipsFound += 1
+							continue
+						}
+					}
+				}
+				// while we found the subdomain with the correct type,
+				// we also need to make sure the list of IPs is
+				// correct. If they are not, we delete the record and
+				// add it again with the correct values.
+				if ipsFound == len(tsIpV4Addresses) {
+					found = true
+					continue
+				} else {
+					l.Printf("will delete %s (incorrect IPv4 addresses)\n", subdomain)
+					recordSetsToDelete = append(recordSetsToDelete, r)
+				}
+			}
+		}
+		if !found {
+			l.Printf("will add %s\n", subdomain)
+			r := &dns.ResourceRecordSet{
+				Name:    subdomain,
+				Type:    "A",
+				Ttl:     TTL,
+				Rrdatas: tsIpV4Addresses,
+			}
+			recordSetsToAdd = append(recordSetsToAdd, r)
+		}
+	}
+
+	// second pass: delete what's not needed
+	for _, r := range existingRecordSets {
+		found := false
+		for _, subdomain := range desiredRecords {
+			subdomain = fmt.Sprintf("%s.%s", subdomain, zone.DnsName)
+			if subdomain == r.Name && r.Type == "A" {
+				found = true
+				continue
+			}
+		}
+		if !found {
+			l.Printf("will delete %s\n", r.Name)
+			recordSetsToDelete = append(recordSetsToDelete, r)
+		}
+	}
+
+	if len(recordSetsToAdd) > 0 || len(recordSetsToDelete) > 0 {
+		change := &dns.Change{Additions: recordSetsToAdd, Deletions: recordSetsToDelete}
+		if _, err := svc.Changes.Create(GCP_PROJECT_NAME, GCP_MANAGED_ZONE, change).Context(ctx).Do(); err != nil {
+			l.Fatalf("failed to apply the change: %+v", err)
+		}
+	}
+}
diff --git a/ts.go b/ts.go
new file mode 100644
index 0000000..94c4b5a
--- /dev/null
+++ b/ts.go
@@ -0,0 +1,82 @@
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+
+	"inet.af/netaddr"
+)
+
+type device struct {
+	Hostname  string   `json:"hostname"`
+	ID        string   `json:"id"`
+	Addresses []string `json:"addresses"`
+}
+
+const (
+	TS_NAME       = "franck.cuny@gmail.com"
+	TS_API_DOMAIN = "api.tailscale.com"
+)
+
+func getTsDevice(ctx context.Context, APIKey, deviceName string) (*device, error) {
+	url := fmt.Sprintf("https://%s/api/v2/tailnet/%s/devices", TS_API_DOMAIN, TS_NAME)
+	req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	req.SetBasicAuth(APIKey, "")
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return nil, err
+	}
+
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("non-ok status code %d returned from tailscale api: %s", resp.StatusCode, resp.Status)
+	}
+	var buf struct {
+		Devices []device `json:"devices"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&buf); err != nil {
+		return nil, err
+	}
+
+	for _, d := range buf.Devices {
+		if d.Hostname == deviceName {
+			return &d, nil
+		}
+	}
+	return nil, fmt.Errorf("could not find the tailscale device named %s", deviceName)
+}
+
+// Get the Tailscale IPv4 and IPv6 addresses associated with the given device.
+func getTsIpsDevice(ctx context.Context, APIKey, device string) ([]string, []string, error) {
+	ts_device, err := getTsDevice(ctx, APIKey, device)
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to get Tailscale device information: %v", err)
+	}
+
+	var (
+		tsIpV4Addresses = []string{}
+		tsIpV6Addresses = []string{}
+	)
+	for _, ipString := range ts_device.Addresses {
+		// we convert the string to a netaddr.IP so we can check if
+		// it's an IP v4 or v6. We need to know what's the version in
+		// order to use it properly when creating/updating the
+		// record. Then we convert it back as a string, since this is
+		// what the DNS API expect.
+		ip := netaddr.MustParseIP(ipString)
+		if ip.Is4() {
+			tsIpV4Addresses = append(tsIpV4Addresses, ip.String())
+		} else {
+			tsIpV6Addresses = append(tsIpV6Addresses, ip.String())
+		}
+	}
+
+	return tsIpV4Addresses, tsIpV6Addresses, nil
+}