This plugin was included in CoreDNS v1.13.0, which is why this repository has been archived.
nomad - DNS interface to Nomad native service discovery.
The nomad plugin serves DNS records for services registered with Nomad. Nomad 1.3+ comes with support for discovering services with an in-built service catalogue that is available via the HTTP API. This plugin extends the HTTP API and provides a DNS interface for querying the service catalogue.
The query can be looked up with the format [service].[namespace].service.nomad. The plugin currently handles A, AAAA and SRV records. Refer to #Usage Example for more details.
job "dns" {
type = "service"
group "dns" {
network {
port "dns" {
static = 1053
// to = 1053
}
}
task "dns" {
driver = "docker"
config {
image = "ghcr.io/ituoga/coredns-nomad:latest"
ports = ["dns"]
args = ["-conf", "/secrets/coredns/Corefile", "-dns.port", "1053"]
}
service {
name = "hostmaster"
provider = "nomad"
port = "dns"
address_mode = "driver"
}
identity {
env = true
}
template {
data = <<EOF
. {
forward . 1.1.1.1
}
service.nomad. {
errors
debug
health
log
nomad {
zone service.nomad
address unix:///secrets/api.sock
ttl 10
}
cache 30
}
EOF
destination = "secrets/coredns/Corefile"
change_mode = "signal"
change_signal = "SIGHUP"
}
}
}
}
nomad {
address URL
token TOKEN
ttl DURATION
}-
addressThe address where a Nomad agent (server) is available. URL defaults tohttp://127.0.0.1:4646. -
tokenThe SecretID of an ACL token to use to authenticate API requests with if the Nomad cluster has ACL enabled. TOKEN defaults to"". -
ttlallows you to set a custom TTL for responses. DURATION defaults to30 seconds. The minimum TTL allowed is0seconds, and the maximum is capped at3600seconds. Setting TTL to 0 will prevent records from being cached. The unit for the value is seconds.
If monitoring is enabled (via the prometheus directive) the following metric is exported:
coredns_nomad_success_requests_total{namespace,server}- Counter of DNS requests handled successfully.coredns_nomad_failed_requests_total{namespace,server}- Counter of DNS requests failed.
The server label indicated which server handled the request. namespace indicates the namespace of the service in the query.
This plugin reports readiness to the ready plugin. It will be ready only when it has successfully connected to the Nomad server. It queries the /v1/agent/self endpoint to check if it is ready.
Enable nomad with and resolve all services with .nomad as the suffix. cache plugin is used to cache the responses for 30 seconds. This avoids a lookup to the Nomad server for every request.
service.nomad.:1053 {
nomad {
zone service.nomad
address http://127.0.0.1:4646
}
cache 30
}
You can see the Corefile.example for a full Corefile example.
nomad plugin uses a default Nomad configuration to create an API client. Options like the HTTP address and the token can be specified in Corefile. However, Nomad Go SDK can also additionally read these environment variables.
NOMAD_TOKENNOMAD_ADDRNOMAD_REGIONNOMAD_NAMESPACENOMAD_HTTP_AUTHNOMAD_CACERTNOMAD_CAPATHNOMAD_CLIENT_CERTNOMAD_CLIENT_KEYNOMAD_TLS_SERVER_NAMENOMAD_SKIP_VERIFY
You can read about them in detail here.
dig redis.default.service.nomad @127.0.0.1 -p 1053
; <<>> DiG 9.18.1-1ubuntu1.2-Ubuntu <<>> redis.default.service.nomad @127.0.0.1 -p 1053
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 54986
;; flags: qr aa rd; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
; COOKIE: bdc9237f49a1f744 (echoed)
;; QUESTION SECTION:
;redis.default.service.nomad. IN A
;; ANSWER SECTION:
redis.default.service.nomad. 10 IN A 192.168.29.76
redis.default.service.nomad. 10 IN A 192.168.29.76
redis.default.service.nomad. 10 IN A 192.168.29.76
;; Query time: 4 msec
;; SERVER: 127.0.0.1#1053(127.0.0.1) (UDP)
;; WHEN: Thu Jan 05 12:12:25 IST 2023
;; MSG SIZE rcvd: 165
Since an A record doesn't contain the port number, SRV record can be used to query the port number of a service.
dig redis.default.service.nomad @127.0.0.1 -p 1053 SRV
; <<>> DiG 9.18.1-1ubuntu1.2-Ubuntu <<>> redis.default.service.nomad @127.0.0.1 -p 1053 SRV
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 49945
;; flags: qr aa rd; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 4
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
; COOKIE: 14572535f3ba6648 (echoed)
;; QUESTION SECTION:
;redis.default.service.nomad. IN SRV
;; ANSWER SECTION:
redis.default.service.nomad. 8 IN SRV 10 10 25395 redis.default.service.nomad.
redis.default.service.nomad. 8 IN SRV 10 10 20888 redis.default.service.nomad.
redis.default.service.nomad. 8 IN SRV 10 10 26292 redis.default.service.nomad.
;; ADDITIONAL SECTION:
redis.default.service.nomad. 8 IN A 192.168.29.76
redis.default.service.nomad. 8 IN A 192.168.29.76
redis.default.service.nomad. 8 IN A 192.168.29.76
;; Query time: 0 msec
;; SERVER: 127.0.0.1#1053(127.0.0.1) (UDP)
;; WHEN: Thu Jan 05 12:12:20 IST 2023
;; MSG SIZE rcvd: 339
$ dig @localhost -p 1053 1dns.default.service.nomad.
; <<>> DiG 9.18.12-0ubuntu0.22.04.2-Ubuntu <<>> @localhost -p 1053 1dns.default.service.nomad.
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 21012
;; 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: 1232
; COOKIE: 6d146bb140b4d8ca (echoed)
;; QUESTION SECTION:
;1dns.default.service.nomad. IN A
;; ANSWER SECTION:
1dns.default.service.nomad. 5 IN SOA ns1.1dns.default.service.nomad. ns1.1dns.default.service.nomad. 1 3600 600 604800 3600
;; Query time: 0 msec
;; SERVER: 127.0.0.1#1053(localhost) (UDP)
;; WHEN: Wed Aug 23 21:14:41 EEST 2023
;; MSG SIZE rcvd: 189
This plugin is intended to appear twoard the end of the plugin list, usually near the proxy plugin declaration.
nomad:github.com/ituoga/coredns-nomad