infra: enabling monitoring for our DNS seeders

[gustavovalverde]

We've had recent incidents with our DNS seeders, but there's no warnings or logs to confirm what's happening, we should fix this and monitor the seeders to be alerted if they're down.

Error: Server is down (SERVFAIL)

$ dig mainnet.seeder.zfnd.org 

; <<>> DiG 9.10.6 <<>> mainnet.seeder.zfnd.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 38927
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;mainnet.seeder.zfnd.org.	IN	A

;; Query time: 1616 msec
;; SERVER: 9.9.9.9#53(9.9.9.9)
;; WHEN: Thu Jul 13 06:37:27 AEST 2023
;; MSG SIZE  rcvd: 52

$ dig tesnet.seeder.zfnd.org

# same error as above

Internal failure: Not enough IP addresses

Like "expected behaviour", but:

• mainnet has less than 20 IP addresses
• testnet has less than 4 IP addresses

Expected behaviour: healthy seeder

$ dig mainnet.seeder.zfnd.org

; <<>> DiG 9.10.6 <<>> mainnet.seeder.zfnd.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 46619
;; flags: qr rd ra; QUERY: 1, ANSWER: 25, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;mainnet.seeder.zfnd.org.	IN	A

;; ANSWER SECTION:
mainnet.seeder.zfnd.org. 600	IN	A	159.223.125.59
mainnet.seeder.zfnd.org. 600	IN	A	47.242.184.215
mainnet.seeder.zfnd.org. 600	IN	A	111.90.145.162
mainnet.seeder.zfnd.org. 600	IN	A	162.19.87.127
mainnet.seeder.zfnd.org. 600	IN	A	37.59.32.10
mainnet.seeder.zfnd.org. 600	IN	A	194.135.81.61
mainnet.seeder.zfnd.org. 600	IN	A	52.28.203.21
mainnet.seeder.zfnd.org. 600	IN	A	51.222.254.36
mainnet.seeder.zfnd.org. 600	IN	A	45.77.105.206
mainnet.seeder.zfnd.org. 600	IN	A	35.227.15.180
mainnet.seeder.zfnd.org. 600	IN	A	44.197.66.202
mainnet.seeder.zfnd.org. 600	IN	A	178.234.34.18
mainnet.seeder.zfnd.org. 600	IN	A	47.198.223.60
mainnet.seeder.zfnd.org. 600	IN	A	46.4.50.226
mainnet.seeder.zfnd.org. 600	IN	A	51.79.230.103
mainnet.seeder.zfnd.org. 600	IN	A	162.55.103.190
mainnet.seeder.zfnd.org. 600	IN	A	8.219.76.216
mainnet.seeder.zfnd.org. 600	IN	A	20.47.97.70
mainnet.seeder.zfnd.org. 600	IN	A	203.96.179.202
mainnet.seeder.zfnd.org. 600	IN	A	95.217.78.170
mainnet.seeder.zfnd.org. 600	IN	A	65.109.81.77
mainnet.seeder.zfnd.org. 600	IN	A	51.77.64.51
mainnet.seeder.zfnd.org. 600	IN	A	185.225.113.103
mainnet.seeder.zfnd.org. 600	IN	A	34.148.244.158
mainnet.seeder.zfnd.org. 600	IN	A	34.148.55.92

;; Query time: 405 msec
;; SERVER: 9.9.9.9#53(9.9.9.9)
;; WHEN: Fri Jul 14 06:35:09 AEST 2023
;; MSG SIZE  rcvd: 452


$ dig testnet.seeder.zfnd.org

; <<>> DiG 9.10.6 <<>> testnet.seeder.zfnd.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 51531
;; flags: qr rd ra; QUERY: 1, ANSWER: 7, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;testnet.seeder.zfnd.org.	IN	A

;; ANSWER SECTION:
testnet.seeder.zfnd.org. 300	IN	A	58.165.15.228
testnet.seeder.zfnd.org. 300	IN	A	34.148.133.41
testnet.seeder.zfnd.org. 300	IN	A	34.133.1.44
testnet.seeder.zfnd.org. 300	IN	A	65.109.80.83
testnet.seeder.zfnd.org. 300	IN	A	192.166.217.71
testnet.seeder.zfnd.org. 300	IN	A	34.134.102.112
testnet.seeder.zfnd.org. 300	IN	A	157.245.113.22

;; Query time: 438 msec
;; SERVER: 9.9.9.9#53(9.9.9.9)
;; WHEN: Fri Jul 14 06:34:42 AEST 2023
;; MSG SIZE  rcvd: 164

[gustavovalverde]

Closed with ZcashFoundation/infra-monitoring-kuma#1