私は2つの理由で大丈夫だと認識しています。

• Dockerの内部DNSも常に圧縮をしているため。 https://github.com/docker/libnetwork/blob/master/resolver.go#L537
• ライブラリの内部で圧縮可能かどうか検査しているため https://github.com/miekg/dns/blob/master/msg.go#L767

Thanks!!!

fixed: #4478

Bug Report

Worker DNS does not do Message compression when returning a response, so it returns with a large response

Steps to Reproduce

execute task https://gist.github.com/int-tt/e814b3886fc362ce2d03c11f2a86956d#file-use-worker-dns-yaml

Expected Results

execute task or use inttt/concourse:dev-set-compress image https://gist.github.com/int-tt/e814b3886fc362ce2d03c11f2a86956d#file-external-dns-yaml

DNS reponse with message compression returned

; <<>> DiG 9.14.3 <<>> ecr-emulate.lnteger.dev @8.8.8.8
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 15180
;; flags: qr rd ra; QUERY: 1, ANSWER: 7, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;ecr-emulate.lnteger.dev.       IN      A

;; ANSWER SECTION:
ecr-emulate.lnteger.dev. 3      IN      CNAME   proxy-ap-n-proxylb-1r9iukj5vmg6a-733833415.lnteger.dev.
proxy-ap-n-proxylb-1r9iukj5vmg6a-733833415.lnteger.dev. 3 IN A 192.168.0.1
proxy-ap-n-proxylb-1r9iukj5vmg6a-733833415.lnteger.dev. 3 IN A 192.168.0.2
proxy-ap-n-proxylb-1r9iukj5vmg6a-733833415.lnteger.dev. 3 IN A 192.168.0.3
proxy-ap-n-proxylb-1r9iukj5vmg6a-733833415.lnteger.dev. 3 IN A 192.168.0.4
proxy-ap-n-proxylb-1r9iukj5vmg6a-733833415.lnteger.dev. 3 IN A 192.168.0.5
proxy-ap-n-proxylb-1r9iukj5vmg6a-733833415.lnteger.dev. 3 IN A 192.168.0.6

;; Query time: 8 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Sat Sep 21 11:05:47 UTC 2019
;; MSG SIZE  rcvd: 205

Actual Results

DNS reponse with no message compression returned

; <<>> DiG 9.14.3 <<>> ecr-emulate.lnteger.dev
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 28183
;; flags: qr rd ra; QUERY: 1, ANSWER: 7, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;ecr-emulate.lnteger.dev.       IN      A

;; ANSWER SECTION:
ecr-emulate.lnteger.dev. 2      IN      CNAME   proxy-ap-n-proxylb-1r9iukj5vmg6a-733833415.lnteger.dev.
proxy-ap-n-proxylb-1r9iukj5vmg6a-733833415.lnteger.dev. 2 IN A 192.168.0.1
proxy-ap-n-proxylb-1r9iukj5vmg6a-733833415.lnteger.dev. 2 IN A 192.168.0.2
proxy-ap-n-proxylb-1r9iukj5vmg6a-733833415.lnteger.dev. 2 IN A 192.168.0.3
proxy-ap-n-proxylb-1r9iukj5vmg6a-733833415.lnteger.dev. 2 IN A 192.168.0.4
proxy-ap-n-proxylb-1r9iukj5vmg6a-733833415.lnteger.dev. 2 IN A 192.168.0.5
proxy-ap-n-proxylb-1r9iukj5vmg6a-733833415.lnteger.dev. 2 IN A 192.168.0.6

;; Query time: 9 msec
;; SERVER: 172.19.0.4#53(172.19.0.4)
;; WHEN: Sat Sep 21 10:58:30 UTC 2019
;; MSG SIZE  rcvd: 563

Additional Context

When running on docker-compose, it is confirmed that the packet flows as follows

Version Info

• Concourse version: 5.5.1
• Deployment type (BOSH/Docker/binary): Dokcer (use https://github.com/concourse/concourse-docker/blob/master/docker-compose.yml)
• Infrastructure/IaaS: anywhere