MyDynDNS

---

A client for the mydyndns dynamic DNS service, providing an application library, CLI tools, and agent process for keeping DNS entries up-to-date.

Features

Command Line Interface

An extensive CLI exists for interacting with the MyDynDNS API:

Example Usage

# Show the current public IP for this host:
$ mydyndns api my-ip --config-file mydyndns.toml
1.2.3.4

# Request an update to the DNS alias for the dynamic DNS host:
$ mydyndns api update-alias --config-file mydyndns.toml
1.2.3.4

Configuration

The CLI contains built-in support for generating and validating config files:

# Generate mydyndns.toml with validated custom options:
$ mydyndns config write toml \
    --validate \
    --api-url=https://example.com --api-key=secret \
    --interval=1h --log-verbosity=1

# Generate mydyndns.json populated default values:
$ mydyndns config write json --defaults

# Generate /var/mydyndns/conf.yml populated with default values:
$ mydyndns config write /var/mydyndns/conf.yml --defaults
$ mydyndns config write conf.yml --directory /var/mydyndns --defaults

Configuration sources

In addition to configuration files, environment variables may be provided in place of file-based configuration directives, as well as command-line flags. Environment variables must be prefixed with MYDYNDNS_, be upper-cased, and use underscores instead of dashes.

As an example, the following directives are equivalent means of providing a base URL for a remote MyDynDNS service API:

1. As a command-line flag: --api-url=https://example.com
2. As an environment variable: MYDYNDNS_API_URL=https://example.com
3. As a line in a configuration file (e.g. toml): api-url = https://example.com

Note that the above list is in order of precedence – a configuration directive provided as a command-line flag will take precedence over a conflicting environment variable, etc.

Notes:

• By default, the CLI looks for a configuration file called mydyndns.ext in the current working directory, where .ext is any supported config file extension. The source directory and/or filename can be customized by providing the --config-path and/or --config-file CLI flags, respectively.
• Configuration files generated with the --defaults CLI flag are not inherently valid and require customizations before they may be used successfully.
• See mydyndns help config for more information.

Completion

The CLI fully supports tab completion through Cobra. You can run mydyndns help completion for instructions on how to generate and enable completions.

Additional Help

Help for every command is available by appending the -h / --help flag to any command.

CLI Agent Process

The CLI provides support for a long-running (daemon) process that can be used as a local service for monitoring changes to the host's (dynamic) IP address and requesting the MyDynDNS service to update DNS records accordingly.

To run in a terminal:

# Assume a valid and discoverable config file exists in the current working directory
$ mydyndns agent start
level=info msg="Initialized with IP address after DNS update" ip=1.2.3.4 ts=2022-01-02T15:04:05.552333-07:00
^Clevel=warn msg="Agent stopped" ts=2022-01-02T15:06:07.744942-07:00
task: signal received: interrupt

Notes:

• The amount of information logged by the agent can be controlled via the -v / --log-verbosity flag or by adjusting the log-verbosity config file directive.
• The SIGINT signal (ctrl-c) requests a graceful shutdown of the agent process.

Client SDK

A package is made available for interacting with the API in other applications:

package main

import (
	"fmt"
	"github.com/TylerHendrickson/mydyndns/pkg/sdk"
	"net"
	"os"
)

func main() {
	var currentIP net.IP

	c := sdk.NewClient("https://example.com/mydyndns-service", os.Getenv("MYDYNDNS_API_KEY"))
	fmt.Println("Fetching my IP address...")
	if ip, err := c.MyIP(); err != nil {
		panic(err)
	} else {
		fmt.Println("My IP address is:", ip)
		currentIP = ip
	}

	if ips, err := net.LookupIP(os.Getenv("MYDYNDNS_MANAGED_HOSTNAME")); err != nil {
		panic(err)
	} else if len(ips) != 1 {
		panic("there should be exactly 1 aliased IP address!")
	} else {
		aIP := ips[0]
		if !aIP.Equal(currentIP) {
			fmt.Println("Requesting DNS update...")
			if ip, err := c.UpdateAlias(); err != nil {
				panic(fmt.Errorf("error requesting DNS update: %w", err))
			} else {
				fmt.Println("DNS alias will point to:", ip)
			}
		}
	}
}

Agent Library

The Agent behavior is available as an importable package that can be configured and executed from other libraries and applications.

package main

import (
	"context"
	"fmt"
	"os"
	"os/signal"
	"syscall"
	"time"

	"github.com/TylerHendrickson/mydyndns/pkg/agent"
	"github.com/TylerHendrickson/mydyndns/pkg/sdk"
	"github.com/go-kit/log"
)

func main() {
	c := sdk.NewClient("https://example.com/mydyndns-service", os.Getenv("MYDYNDNS_API_KEY"))
	logger := log.NewJSONLogger(os.Stderr)

	// SIGINT cancels context
	ctx, cancel := signal.NotifyContext(context.Background(), syscall.SIGINT, os.Interrupt)
	defer cancel()

	// Start an agent that checks syncs DNS with the IP every 1 hour
	// until CTRL+C sends SIGINT for graceful shutdown.
	// Note: this function call is safe for concurrent use and may be wrapped in a goroutine.
	err := agent.Run(ctx, logger, c, time.Hour)
	if err != nil {
		fmt.Printf("Failed to run agent: %s\n", err)
	}
}

Using

go install

The easiest way to install this program is to clone the repository, navigate to mydyndns, and run go install ./cmd/mydyndns from within the cloned repository. This will compile the proper binary for your operating system and place it in your Go binaries path (e.g. $GOBIN, $GOPATH/bin, etc.).

Alternatively, run go install github.com/TylerHendrickson/mydyndns/cmd/mydyndns@latest to install without cloning.

go get

Use go get -u github.com/TylerHendrickson/mydyndns/pkg/sdk and/or go get -u github.com/TylerHendrickson/mydyndns/pkg/agent to make this available for use in your own Go application.

Precompiled Binary

See the releases page to download the appropriate archive for your platform. You can find the latest release here.

Example:

$ wget https://github.com/TylerHendrickson/mydyndns/releases/download/0.2.4/mydyndns_0.2.4_windows_arm64.zip
$ tar xvfz mydyndns_*.tar.gz mydyndns
$ mv ./mydyndns /usr/bin/mydyndns

Docker

The CLI application is available as a Docker image, hosted by GitHub's container registry. View released images here.

Using docker-compose

Using docker-compose to run the agent is relatively straightforward:

version: "3.6"
services:
  mydyndns:
    image: ghcr.io/tylerhendrickson/mydyndns:latest
    container_name: mydyndns-agent
    command: agent start
    environment:
      - TZ
      - PUID
      - PGID
      - MYDYNDNS_CONFIG_PATH=/config
    volumes:
      - ./mydyndns:/config:ro
    restart: unless-stopped

In this example, configuration is sourced from file within a volume mounted at /config in the container, e.g. /config/mydyndns.toml. However, all usual means of configuration are still supported; parameters may be provided via the environment section, as well as by passing additional flags in the command directive. Note that all environment variables must be prefixed with MYDYNDNS_.

Developing

This project uses Taskfile.yml to manage common development tasks (instead of using make). Install Task, then run task --list to see a list of available tasks for this project, or task --help for more information about using this system.