Consul 服务注册和查询

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前文我们已经简单介绍 Consul 的安装和启动了，本篇我们来开始在 consul 中注册和使用 service

定义 service

Service 可以通过 service 定义或者 API 调用进行注册，但是使用配置文件定义是最通用的形式。

首先创建一个目录用来存放配置文件，Consul 会从配置目录中加载所有配置文件，一种在 unix 系统中通用的做法是在定义一个 /etc/consul.d 目录。

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mkdir consul.d

然后创建一个文件用来存放我们定义的服务，在这个配置中我们还提供了一个 tag 用来做服务查询：

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$ echo '{"service": {"name": "web", "tags": ["python"], "port": 8888}}' | tee consul.d/web.json

这里我们定义了名称是 web 并且跑在 8888 端口的 web 服务。

重启 agent 并且提供配置目录：

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consul agent -dev -node=zhaoyongqiang -config-dir=consul.d
==> Starting Consul agent...
==> Consul agent running!
           Version: 'v1.0.0'
           Node ID: '2705278f-db30-b1a8-9607-1107a4524395'
         Node name: 'zhaoyongqiang'
        Datacenter: 'dc1' (Segment: '<all>')
            Server: true (Bootstrap: false)
       Client Addr: [127.0.0.1] (HTTP: 8500, HTTPS: -1, DNS: 8600)
      Cluster Addr: 127.0.0.1 (LAN: 8301, WAN: 8302)
           Encrypt: Gossip: false, TLS-Outgoing: false, TLS-Incoming: false

==> Log data will now stream in as it occurs:

    2017/11/16 11:36:32 [DEBUG] Using random ID "2705278f-db30-b1a8-9607-1107a4524395" as node ID
    2017/11/16 11:36:32 [INFO] raft: Initial configuration (index=1): [{Suffrage:Voter ID:2705278f-db30-b1a8-9607-1107a4524395 Address:127.0.0.1:8300}]
    2017/11/16 11:36:32 [INFO] raft: Node at 127.0.0.1:8300 [Follower] entering Follower state (Leader: "")
    2017/11/16 11:36:32 [INFO] serf: EventMemberJoin: zhaoyongqiang.dc1 127.0.0.1
    2017/11/16 11:36:32 [INFO] serf: EventMemberJoin: zhaoyongqiang 127.0.0.1
    2017/11/16 11:36:32 [INFO] consul: Handled member-join event for server "zhaoyongqiang.dc1" in area "wan"
    2017/11/16 11:36:32 [INFO] consul: Adding LAN server zhaoyongqiang (Addr: tcp/127.0.0.1:8300) (DC: dc1)
    2017/11/16 11:36:32 [INFO] agent: Started DNS server 127.0.0.1:8600 (udp)
    2017/11/16 11:36:32 [INFO] agent: Started DNS server 127.0.0.1:8600 (tcp)
    2017/11/16 11:36:32 [INFO] agent: Started HTTP server on 127.0.0.1:8500 (tcp)
    2017/11/16 11:36:32 [WARN] raft: Heartbeat timeout from "" reached, starting election
    2017/11/16 11:36:32 [INFO] raft: Node at 127.0.0.1:8300 [Candidate] entering Candidate state in term 2
    2017/11/16 11:36:32 [DEBUG] raft: Votes needed: 1
    2017/11/16 11:36:32 [DEBUG] raft: Vote granted from 2705278f-db30-b1a8-9607-1107a4524395 in term 2. Tally: 1
    2017/11/16 11:36:32 [INFO] raft: Election won. Tally: 1
    2017/11/16 11:36:32 [INFO] raft: Node at 127.0.0.1:8300 [Leader] entering Leader state
    2017/11/16 11:36:32 [INFO] consul: cluster leadership acquired
    2017/11/16 11:36:32 [INFO] consul: New leader elected: zhaoyongqiang
    2017/11/16 11:36:32 [DEBUG] consul: Skipping self join check for "zhaoyongqiang" since the cluster is too small
    2017/11/16 11:36:32 [INFO] consul: member 'zhaoyongqiang' joined, marking health alive
    2017/11/16 11:36:32 [INFO] agent: Synced service 'web'

注意输出包含了 “synced” the web service，consul 已经成功把定义的服务导入 service catlog 了。

查询服务

一旦服务注册之后，我们就可以使用 DNS 或者 HTTP 的方式查询 service 了。

DNS 查询

服务注册之后可以通过 DNS 进行服务查询，service 的 DNS name 是 NAME.service.consul，默认情况下所有的 DNS names 总是在 consul namespace 中，namespace 可以进行 配置 ，service 的 subdomain 用来告知 Consul 我们需要查询的 service 名称，在这里就是 NAME：

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% dig @127.0.0.1 -p 8600 web.service.consul                                                                          

; <<>> DiG 9.8.3-P1 <<>> @127.0.0.1 -p 8600 web.service.consul
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 25186
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;web.service.consul.        IN  A

;; ANSWER SECTION:
web.service.consul. 0   IN  A   127.0.0.1

;; Query time: 87 msec
;; SERVER: 127.0.0.1#8600(127.0.0.1)
;; WHEN: Thu Nov 16 11:46:31 2017
;; MSG SIZE  rcvd: 52

可以看到一个带有节点 ip 的 record 会返回，record 只能 hold IP address。

我们也可以通过 DNS 查询完整的 address/port pair:

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± % dig @127.0.0.1 -p 8600 web.service.consul SRV

; <<>> DiG 9.8.3-P1 <<>> @127.0.0.1 -p 8600 web.service.consul SRV
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50494
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 2
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;web.service.consul.        IN  SRV

;; ANSWER SECTION:
web.service.consul. 0   IN  SRV 1 1 8888 zhaoyongqiang.node.dc1.consul.

;; ADDITIONAL SECTION:
zhaoyongqiang.node.dc1.consul. 0 IN A   127.0.0.1
zhaoyongqiang.node.dc1.consul. 0 IN TXT "consul-network-segment="

;; Query time: 36 msec
;; SERVER: 127.0.0.1#8600(127.0.0.1)
;; WHEN: Fri Nov 17 16:19:30 2017
;; MSG SIZE  rcvd: 137

SRV 记录表明 web service 在端口 8888 上并且存在于 zhaoyongqiang.node.dc1.consul 这个节点上。

我们也可以使用 tag 过滤需要出现的 web service，形如 TAG.NAME.service.consul，比如使用我们定义 service 时使用的 tag python：

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dig @127.0.0.1 -p 8600 python.web.service.consul

; <<>> DiG 9.8.3-P1 <<>> @127.0.0.1 -p 8600 rails.web.service.consul
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 14331
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; WARNING: recursion requested but not available

;; QUESTION SECTION:
;rails.web.service.consul.  IN  A

;; ANSWER SECTION:
rails.web.service.consul. 0 IN  A   127.0.0.1

;; Query time: 15 msec
;; SERVER: 127.0.0.1#8600(127.0.0.1)
;; WHEN: Fri Nov 17 16:23:39 2017
;; MSG SIZE  rcvd: 58

HTTP 查询

除了 DNS 也可以使用 HTTP 的方式查询 web service

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± % curl http://localhost:8500/v1/catalog/service/web

[
    {
        "ID": "2705278f-db30-b1a8-9607-1107a4524395",
        "Node": "zhaoyongqiang",
        "Address": "127.0.0.1",
        "Datacenter": "dc1",
        "TaggedAddresses": {
            "lan": "127.0.0.1",
            "wan": "127.0.0.1"
        },
        "NodeMeta": {
            "consul-network-segment": ""
        },
        "ServiceID": "web",
        "ServiceName": "web",
        "ServiceTags": [
            "python"
        ],
        "ServiceAddress": "",
        "ServicePort": 8888,
        "ServiceEnableTagOverride": false,
        "CreateIndex": 6,
        "ModifyIndex": 6
    }
]

http api 可以返回所有定义了该服务的节点信息，稍后我们在 health checks 会看到，通常情况下你指向查询健康状态是 passing 的实例节点。

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curl 'http://localhost:8500/v1/health/service/web?passing'
[
    {
        "Node": {
            "ID": "db363ec4-ba40-8563-fa35-b9fd762aaf2b",
            "Node": "zhaoyongqiang",
            "Address": "127.0.0.1",
            "Datacenter": "dc1",
            "TaggedAddresses": {
                "lan": "127.0.0.1",
                "wan": "127.0.0.1"
            },
            "Meta": {
                "consul-network-segment": ""
            },
            "CreateIndex": 5,
            "ModifyIndex": 6
        },
        "Service": {
            "ID": "web",
            "Service": "web",
            "Tags": [
                "python"
            ],
            "Address": "",
            "Port": 8888,
            "EnableTagOverride": false,
            "CreateIndex": 6,
            "ModifyIndex": 6
        },
        "Checks": [
            {
                "Node": "zhaoyongqiang",
                "CheckID": "serfHealth",
                "Name": "Serf Health Status",
                "Status": "passing",
                "Notes": "",
                "Output": "Agent alive and reachable",
                "ServiceID": "",
                "ServiceName": "",
                "ServiceTags": [],
                "CreateIndex": 5,
                "ModifyIndex": 5
            }
        ]
    }
]

更新 service

service 更新可以通过重新定义配置文件或者 HTTP 接口进行更新，更新配置文件可以向 agent 发送 SIGHUP 来达到不重启服务而更新配置的目的。

参考资料

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