multipass

Name

multipass - dynamically adds machines created with multipass to a zone.

Description

The multipass plugin adds A records to a zone for all the VMs managed by Canonical's multipass.

The plugin will match the first part of the request to the VM name and use the first IPv4 address of the VM as A record in the response (it could be possible to answer all the IPs, but I do not need it).

The plugin calls the multipass binary with the list command and the --format=json flags. So you need a working multipass client in the same machine that CoreDNS is running.

But Why?

multipass uses macos' virtualization framework to create the virtual machines. The virtualization framework uses an isolated network, so you can't for example use your network's DHCP+DNS servers to access the machines. mDNS is not great for general purposes.

Using CoreDNS as resolver for your machine, allows you to have more flexibility and the multipass plugins gives you automatic DNS resolution for all the machines managed by multipass.

Compilation

The plugin should be used as an external plugin:

go get github.com/ralgozino/coredns-multipass
download CoreDNS source code
add multipass:github.com/ralgozino/coredns-multipass to plugin.cfg
build CoreDNS.

Notice that the order of the plugins in plugin.cfg is the order in which they will be run.

Ready

This plugin reports readiness to the ready plugin. It will be ready only when it has successfully retrieved a list of VMs from multipass.

Examples

Consider the following Corefile:

example.org:1053 {
    multipass
}

and that the following VM has been created with multipass:

$ multipass list
Name                    State             IPv4             Image
primary                 Running           192.168.64.127   Ubuntu 22.04 LTS

querying CoreDNS for primary.example.org will return 192.168.64.127:

$ dig @127.0.0.1 -p 1053 primary.example.org

; <<>> DiG 9.10.6 <<>> @127.0.0.1 -p 1053 primary.example.org
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 35613
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;primary.example.org.		IN	A

;; ANSWER SECTION:
primary.example.org.	3600	IN	A	192.168.64.127

;; Query time: 560 msec
;; SERVER: 127.0.0.1#1053(127.0.0.1)
;; WHEN: Thu May 11 16:27:51 CEST 2023
;; MSG SIZE  rcvd: 83

Remote multipass

You can tell the multipass client to connect to a remote multipass daemon by setting the MULTIPASS_SERVER_ADDRESS=<hostname:port> environment variable. Setting the environment variable while starting CoreDNS will also work:

$ MULTIPASS_SERVER_ADDRESS=<hostname:port> coredns [parameters]

You might need to set client authentication for it to work.

References:

ralgozino / coredns-multipass