ConsulのDNSラウンドロビンの検証

June 6, 2014

Consul - hashicorp を利用しDNS Failoverを検証した

Consul v0.2.0

TL;DR

hostnameやserviceなどでDNSを設定し
DNSはnodeの死活監視によって動的に生まれ死んでいく。
nodeとは別にserviceという概念があり、DNSラウンドロビンが行える

loopback alias

@keita氏に教えてもらった
Mac OS X – Adding a loopback alias - THE DANGLING POINTER

このloopbackのaliasが大変役に立った。

nodeの用意

127.0.0.1(node01)
127.0.0.2(node02)
127.0.0.3(node03)

$ ifconfig lo0 alias 127.0.0.2
$ ifconfig lo0 alias 127.0.0.3

設定ファイルのディレクトリの用意

$ mkdir ./node01
$ mkdir ./node02
$ mkdir ./node03

設定ファイルの作成

node01/config.json

Web UI用のデータはここからダウンロードして
ui_dirにて指定してディレクトリへ配置する。

{
  "node_name": "node01",
  "data_dir": "./node01/",
  "bind_addr": "127.0.0.1",
  "client_addr": "127.0.0.1",
  "ui_dir": "./node01/",
  "domain": "foo",
  "bootstrap": true,
  "server": true
}

node01/check.json

{
  "service": {
      "name": "echo",
      "tags": ["master"],
      "check": {
          "script": "echo 'hello'",
          "interval": "10s"
      }
  }
}

node02/config.json

{
  "node_name": "node02",
  "data_dir": "./node02/",
  "bind_addr": "127.0.0.2",
  "client_addr": "127.0.0.2",
  "ui_dir": "./node02/",
  "domain": "foo",
  "bootstrap": true,
  "server": true
}

node02/check.json

{
  "service": {
      "name": "echo",
      "tags": ["slave"],
      "check": {
          "script": "echo 'hello'",
          "interval": "10s"
      }
  }
}

node03/config.json

{
  "node_name": "node03",
  "data_dir": "./node03/",
  "bind_addr": "127.0.0.3",
  "client_addr": "127.0.0.3",
  "ui_dir": "./node03/",
  "domain": "foo",
  "bootstrap": true,
  "server": true
}

node03/check.json

{
  "service": {
      "name": "echo",
      "tags": ["slave"],
      "check": {
          "script": "echo 'hello'",
          "interval": "10s"
      }
  }
}

nodeの起動

$ sudo consul agent -config-dir node01
$ sudo consul agent -config-dir node02
$ sudo consul agent -config-dir node03

名前解決をしてみる

node01

$ dig @127.0.0.1 -p 8600 node01.node.foo. ANY

; <<>> DiG 9.8.3-P1 <<>> @127.0.0.1 -p 8600 node01.node.foo. ANY
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 3750
;; flags: qr aa rd; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;node01.node.foo.         IN      ANY

;; ANSWER SECTION:
node01.node.foo.  0       IN      A       127.0.0.1

;; Query time: 6 msec
;; SERVER: 127.0.0.1#8600(127.0.0.1)
;; WHEN: Fri Jun  6 01:36:37 2014
;; MSG SIZE  rcvd: 150

$

node02

$ dig @127.0.0.1 -p 8600 node02.node.foo. ANY

; <<>> DiG 9.8.3-P1 <<>> @127.0.0.1 -p 8600 node02.node.foo. ANY
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 3750
;; flags: qr aa rd; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;node02.node.foo.         IN      ANY

;; ANSWER SECTION:
node02.node.foo.  0       IN      A       127.0.0.2

;; Query time: 6 msec
;; SERVER: 127.0.0.1#8600(127.0.0.1)
;; WHEN: Fri Jun  6 01:36:37 2014
;; MSG SIZE  rcvd: 150

$

service

$ dig @127.0.0.1 -p 8600 echo.service.foo. ANY

; <<>> DiG 9.8.3-P1 <<>> @127.0.0.1 -p 8600 echo.service.foo. ANY
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 3750
;; flags: qr aa rd; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;echo.service.foo.         IN      ANY

;; ANSWER SECTION:
echo.service.foo.  0       IN      A       127.0.0.1
echo.service.foo.  0       IN      A       127.0.0.2
echo.service.foo.  0       IN      A       127.0.0.3

;; Query time: 6 msec
;; SERVER: 127.0.0.1#8600(127.0.0.1)
;; WHEN: Fri Jun  6 01:36:37 2014
;; MSG SIZE  rcvd: 150

$

service(master)

$ dig @127.0.0.1 -p 8600 master.echo.service.foo. ANY

; <<>> DiG 9.8.3-P1 <<>> @127.0.0.1 -p 8600 master.echo.service.foo. ANY
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 3750
;; flags: qr aa rd; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;master.echo.service.foo.         IN      ANY

;; ANSWER SECTION:
master.echo.service.foo.  0       IN      A       127.0.0.1

;; Query time: 6 msec
;; SERVER: 127.0.0.1#8600(127.0.0.1)
;; WHEN: Fri Jun  6 01:36:37 2014
;; MSG SIZE  rcvd: 150

$

service(slave)

$ dig @127.0.0.1 -p 8600 slave.echo.service.foo. ANY

; <<>> DiG 9.8.3-P1 <<>> @127.0.0.1 -p 8600 slave.echo.service.foo. ANY
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 3750
;; flags: qr aa rd; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;slave.echo.service.foo.         IN      ANY

;; ANSWER SECTION:
slave.echo.service.foo.  0       IN      A       127.0.0.2
slave.echo.service.foo.  0       IN      A       127.0.0.3

;; Query time: 6 msec
;; SERVER: 127.0.0.1#8600(127.0.0.1)
;; WHEN: Fri Jun  6 01:36:37 2014
;; MSG SIZE  rcvd: 150

$

機能毎のメモ

bootstrapは最初の1台
serverは3~5台ぐらいあったらいい
nodeの名前は各nodeで設定される
serviceは複数設定が可能。DNS Round Robinが行える
tag を設定することでサブドメインが利用可能になる
不要なホスト消す (curl -H “Content-Type: application/json” -d ‘{“Datacenter”: “DATACENTER”, “Node”: “NODENAME”}’ http://localhost:8500/v1/catalog/deregister)

以上、メモになります。