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2 posts with the tag “Go”

restic-monitor: Never Miss a Failed Backup

Steffen Vogel
Steffen Vogel
code poet, bit juggler & logic wizard

I run restic to back up my servers. One day I noticed a repository hadn’t received a new snapshot in weeks. The backup job had been silently failing, and I had no idea.

That’s the worst kind of failure: everything appears fine until you actually need the backup.

TL;DR

Section titled “TL;DR”

/stv0g/restic-monitor is a small Go tool that checks whether each of your restic repositories has a recent enough snapshot and reports the result to an Uptime Kuma push monitor. Run it on a timer and you’ll know within hours if a backup stops working.

FreeCAD + Sylvac = InstrumentInput
FreeCAD + Sylvac = InstrumentInput.

Fritz!DNS - An authoritative DNS server for AVM FRITZ!Box routers

Steffen Vogel
Steffen Vogel
code poet, bit juggler & logic wizard
Fritz!Box
Fritz!Box.

In my home network, I am using an AVM FRITZ!Box Cable 6690. It handles DHCP, DNS, Wifi and recently also interfaces my home network via WireGuard to my servers.


Just like the venerable Dnsmasq AVM’s FRITZ!OS uses hostnames learned from its DHCP leases and makes them resolvable via its internal DNS server.

Unfortunately, this feature in FRITZ!OS has some limitations:

  1. The name of the DNS Zone is hard coded to fritz.box and can not be adjusted. Hence, the resolvable names have the following schema: myhostname.fritz.box
  2. The internal DNS server only supports recursive DNS looks. It does not act as an authoritative DNS server. Hence the local zone can not be delegated.
  3. AXFR zone transfers are not supported.

My solution to these shortcomings is Fritz-DNS which:

  • Is a small tool written in the Go programming language.
  • Is a small authoritative DNS server which serves A / AAAA resource records for local hosts connected to an AVM Fritz Box home WiFi router.
  • Can be used in a hidden master configuration as it supports AXFR zone transfers.
  • Uses the custom extension (X_AVM-DE_GetHostListPath) of the TR-064 Hosts SOAP-API as documented here to retrieve a list of local hosts.
  • Supports the generation of AAAA (IPv6) resource records based on the hosts MAC addresses using 64-Bit Extended Unique Identifier (EUI-64) and a configured unique local address (ULA) prefix.
  • Does not yet support PTR resource records (to be implemented…)
  • Is licensed under the Apache 2.0 license

You can find Fritz-DNS at Codeberg: /stv0g/fritz-dns .

Here is a small figure illustrating the interaction of Fritz-DNS with the Fritz!Box and other DNS servers / clients:

Fritz!DNS Architecture
Fritz!DNS Architecture.

CLI Usage

Section titled “CLI Usage”
Terminal window
$ fritz-dns
Usage of fritz-dns
  -ipv6-ula-prefix string
      Fritz Box IPv6 ULA Prefix (default "fd00::/64")
  -pass string
      FritzBox password
  -port int
      Listen port (default 53)
  -soa-expire duration
      SOA expire value (default 744h0m0s)
  -soa-mbox string
      SOA mailbox value
  -soa-minttl duration
      SOA minimum TTL value (default 1h0m0s)
  -soa-ns string
      Authorative DNS server for the zone
  -soa-refresh duration
      SOA refresh value (default 2h0m0s)
  -soa-retry duration
      SOA retry value (default 1h0m0s)
  -ttl duration
      default TTL values for records (default 5m0s)
  -url string
      FritzBox URL (default "http://fritz.box/")
  -user string
      FritzBox username (default "admin")
  -zone string
      DNS Zone (default "fritz.box.")