ELBのDNS LookupでIPアドレスを8個返すようになりました

横田あかり

2011.10.27

この記事は公開されてから1年以上経過しています。情報が古い可能性がありますので、ご注意ください。

今までのELB

今までのELBはあるDNS名に対して1つのIPアドレスを返していました。このIPアドレスは固定ではなく、ELBの混雑状況によって自動的に変化していました。このDNS名に対するIPアドレスの変更は、クライアントアプリ側のDNSキャッシュ等で不具合を起こす危険性がゼロではなく、実際に私は体験しました。

新しいELB

新しいELBは最大で8つのIPアドレスを返してくれます。これによって、ELBの混雑状況によって拡大したり縮小した場合に、さっきまで見えていたキャッシュしたIPアドレスが見つからないといったエラーが無くなります。

8つのIPアドレスを確認する

digコマンドで確認できます。試してみて勘違いしていたのですが、AZの数に応じて最大で8つのようです。以下はAZ1つの場合で、結果のAレコードは1つでした。

$ dig MyLoadBalancer-83p080071.ap-northeast-1.elb.amazonaws.com

; <<>> DiG 9.7.3-P3 <<>> MyLoadBalancer-83p080071.ap-northeast-1.elb.amazonaws.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 43600
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 8, ADDITIONAL: 8

;; QUESTION SECTION:
;MyLoadBalancer-834080071.ap-northeast-1.elb.amazonaws.com. IN A

;; ANSWER SECTION:
MyLoadBalancer-834080071.ap-northeast-1.elb.amazonaws.com. 36 IN A 176.32.89.84

;; AUTHORITY SECTION:
elb.amazonaws.com.	905	IN	NS	ns-941.amazon.com.
elb.amazonaws.com.	905	IN	NS	ns-927.amazon.com.
elb.amazonaws.com.	905	IN	NS	ns-944.amazon.com.
elb.amazonaws.com.	905	IN	NS	ns-916.amazon.com.
elb.amazonaws.com.	905	IN	NS	ns-947.amazon.com.
elb.amazonaws.com.	905	IN	NS	ns-925.amazon.com.
elb.amazonaws.com.	905	IN	NS	ns-935.amazon.com.
elb.amazonaws.com.	905	IN	NS	ns-934.amazon.com.

;; ADDITIONAL SECTION:
ns-916.amazon.com.	27	IN	A	207.171.178.7
ns-925.amazon.com.	28	IN	A	72.21.208.213
ns-927.amazon.com.	28	IN	A	72.21.204.209
ns-934.amazon.com.	40	IN	A	87.238.84.215
ns-935.amazon.com.	42	IN	A	87.238.80.213
ns-941.amazon.com.	894	IN	A	204.246.160.5
ns-944.amazon.com.	909	IN	A	204.246.161.7
ns-947.amazon.com.	27	IN	A	204.246.162.10

;; Query time: 2 msec
;; SERVER: 192.168.0.3#53(192.168.0.3)
;; WHEN: Thu Oct 27 11:54:17 2011
;; MSG SIZE  rcvd: 394

続いてAZを2つにした場合です。Aレコードが2つになりました！！

$ dig  MyLB1-1168506832.ap-northeast-1.elb.amazonaws.com

; <<>> DiG 9.7.3-P3 <<>> MyLB1-1168506832.ap-northeast-1.elb.amazonaws.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62308
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 8, ADDITIONAL: 8

;; QUESTION SECTION:
;MyLB1-1168506832.ap-northeast-1.elb.amazonaws.com. IN A

;; ANSWER SECTION:
MyLB1-1168506832.ap-northeast-1.elb.amazonaws.com. 60 IN A 46.51.250.132
MyLB1-1168506832.ap-northeast-1.elb.amazonaws.com. 60 IN A 176.32.89.84

;; AUTHORITY SECTION:
elb.amazonaws.com.	2631	IN	NS	ns-934.amazon.com.
elb.amazonaws.com.	2631	IN	NS	ns-916.amazon.com.
elb.amazonaws.com.	2631	IN	NS	ns-925.amazon.com.
elb.amazonaws.com.	2631	IN	NS	ns-935.amazon.com.
elb.amazonaws.com.	2631	IN	NS	ns-944.amazon.com.
elb.amazonaws.com.	2631	IN	NS	ns-941.amazon.com.
elb.amazonaws.com.	2631	IN	NS	ns-947.amazon.com.
elb.amazonaws.com.	2631	IN	NS	ns-927.amazon.com.

;; ADDITIONAL SECTION:
ns-916.amazon.com.	860	IN	A	207.171.178.7
ns-925.amazon.com.	862	IN	A	72.21.208.213
ns-927.amazon.com.	860	IN	A	72.21.204.209
ns-934.amazon.com.	1	IN	A	87.238.84.215
ns-935.amazon.com.	55	IN	A	87.238.84.215
ns-941.amazon.com.	2624	IN	A	204.246.160.5
ns-944.amazon.com.	2638	IN	A	204.246.161.7
ns-947.amazon.com.	862	IN	A	204.246.162.10

;; Query time: 140 msec
;; SERVER: 192.168.0.3#53(192.168.0.3)
;; WHEN: Thu Oct 27 13:30:31 2011
;; MSG SIZE  rcvd: 402

さらに、AZがたくさんあるUSリージョンで試してみます。

$ dig MyLoadBalancer-808957587.us-east-1.elb.amazonaws.com

; <<>> DiG 9.7.3-P3 <<>> MyLoadBalancer-808957587.us-east-1.elb.amazonaws.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 40479
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 8, ADDITIONAL: 8

;; QUESTION SECTION:
;MyLoadBalancer-808957587.us-east-1.elb.amazonaws.com. IN A

;; ANSWER SECTION:
MyLoadBalancer-808957587.us-east-1.elb.amazonaws.com. 60 IN A 107.20.220.100
MyLoadBalancer-808957587.us-east-1.elb.amazonaws.com. 60 IN A 184.73.247.162
MyLoadBalancer-808957587.us-east-1.elb.amazonaws.com. 60 IN A 107.20.162.34
MyLoadBalancer-808957587.us-east-1.elb.amazonaws.com. 60 IN A 107.20.177.26

;; AUTHORITY SECTION:
elb.amazonaws.com.	736	IN	NS	ns-916.amazon.com.
elb.amazonaws.com.	736	IN	NS	ns-941.amazon.com.
elb.amazonaws.com.	736	IN	NS	ns-934.amazon.com.
elb.amazonaws.com.	736	IN	NS	ns-944.amazon.com.
elb.amazonaws.com.	736	IN	NS	ns-925.amazon.com.
elb.amazonaws.com.	736	IN	NS	ns-947.amazon.com.
elb.amazonaws.com.	736	IN	NS	ns-927.amazon.com.
elb.amazonaws.com.	736	IN	NS	ns-935.amazon.com.

;; ADDITIONAL SECTION:
ns-916.amazon.com.	767	IN	A	207.171.178.7
ns-925.amazon.com.	770	IN	A	72.21.208.213
ns-927.amazon.com.	769	IN	A	72.21.204.209
ns-934.amazon.com.	55	IN	A	87.238.84.215
ns-935.amazon.com.	48	IN	A	87.238.84.215
ns-941.amazon.com.	744	IN	A	204.246.160.5
ns-944.amazon.com.	745	IN	A	204.246.161.7
ns-947.amazon.com.	767	IN	A	204.246.162.10

;; Query time: 113 msec
;; SERVER: 192.168.0.3#53(192.168.0.3)
;; WHEN: Thu Oct 27 13:51:48 2011
;; MSG SIZE  rcvd: 437

今度は4つAレコード返ってきました！こんな感じで最大8個まで返してくれるんですね。

ちなみに、今までのELBを使っている場合には、3週間以内に新しいELBに切り替わるようです。