Confd是一个轻量级的配置管理工具。

通过查询Etcd，结合配置模板引擎，保持本地配置最新，同时具备定期探测机制，配置变更自动reload。
其后端支持的数据类型有：etcd、consul、vault、environment variables、redis、zookeeper、dynamodb、stackengine、rancher。不过一般使用Confd和etcd的配合使用比较多。
其常用架构如下：
这里写图片描述

一、简单配置

1、配置etcd数据

具体步骤这里略过，这里只配置两条数据

etcdctl set /myapp/database/url www.361way.com
etcdctl set /myapp/database/user rob

2、confd安装

confd比较简单就一个文件，拿过来就可以执行，可以从github上下载：https://github.com/kelseyhightower/confd/releases ，并将其放到/usr/local/bin目录下即可。不过使用前需要创建相应的配置目录：

[root@etcd1 bin]# mkdir -p /etc/confd/{conf.d,templates}

3、创建confd配置文件

# vim  /etc/confd/conf.d/myconfig.toml
[template]
src = "myconfig.conf.tmpl"
dest = "/tmp/myconfig.conf"
keys = [
    "/myapp/database/url",
    "/myapp/database/user",
]

4、创建模板文件

# vim /etc/confd/templates/myconfig.conf.tmpl
[myconfig]
database_url = {{getv "/myapp/database/url"}}
database_user = {{getv "/myapp/database/user"}}

5、执行生成配置文件

confd -onetime -backend etcd -node http://127.0.0.1:2379    只一次
confd -interval=60 -backend etcd -node http://127.0.0.1:2379 &   按时间轮询
使用onetime参数的，配置文件生成一次后，confd程序就退出了，下面的那句，会每隔60秒轮询一次。一旦后端etcd相应的值发生变化就会重新生成相应的配置文件。

6、验证文件生成

[root@etcd1 tmp]# cat /tmp/myconfig.conf
[myconfig]
database_url = www.361way.com
database_user = rob

二、etcd+confd+nginx配置

1、创建数据

etcdctl set /myapp/subdomain myapp
etcdctl set /myapp/upstream/app2 "10.0.1.100:80"
etcdctl set /myapp/upstream/app1 "10.0.1.101:80"
etcdctl set /yourapp/subdomain yourapp
etcdctl set /yourapp/upstream/app2 "10.0.1.102:80"
etcdctl set /yourapp/upstream/app1 "10.0.1.103:80"

2、创建配置文件

# cat /etc/confd/conf.d/myapp-nginx.toml
[template]
prefix = "/myapp"
src = "nginx.tmpl"
dest = "/tmp/myapp.conf"
owner = "nginx"
mode = "0644"
keys = [
  "/subdomain",
  "/upstream",
]
check_cmd = "/usr/sbin/nginx -t -c {{.src}}"
reload_cmd = "/usr/sbin/service nginx reload"
# cat /etc/confd/conf.d/yourapp-nginx.toml
[template]
prefix = "/yourapp"
src = "nginx.tmpl"
dest = "/tmp/yourapp.conf"
owner = "nginx"
mode = "0644"
keys = [
  "/subdomain",
  "/upstream",
]
check_cmd = "/usr/sbin/nginx -t -c {{.src}}"
reload_cmd = "/usr/sbin/service nginx reload"

这里创建了两个配置文件。接下来创建一个模板文件，两个配置文件会根据该模板文件生成配置：

# cat /etc/confd/templates/nginx.tmpl
upstream {{getv "/subdomain"}} {
{{range getvs "/upstream/*"}}
    server {{.}};
{{end}}
}
server {
    server_name  {{getv "/subdomain"}}.example.com;
    location / {
        proxy_pass        http://{{getv "/subdomain"}};
        proxy_redirect    off;
        proxy_set_header  Host             $host;
        proxy_set_header  X-Real-IP        $remote_addr;
        proxy_set_header  X-Forwarded-For  $proxy_add_x_forwarded_for;
   }
}

3、验证

在进行验证启用的时候，会发现有如下报错：

[root@etcd1 conf.d]# 2017-05-08T19:06:07+08:00 etcd1 confd[10949]: INFO Target config /tmp/myapp.conf out of sync
2017-05-08T19:06:07+08:00 etcd1 confd[10949]: ERROR "nginx: [emerg] \"upstream\" directive is not allowed here in /tmp/.myapp.conf835093196:1\nnginx: configuration file /tmp/.myapp.conf835093196 test failed\n"
2017-05-08T19:06:07+08:00 etcd1 confd[10949]: ERROR Config check failed: exit status 1
2017-05-08T19:06:07+08:00 etcd1 confd[10949]: INFO Target config /tmp/yourapp.conf out of sync
2017-05-08T19:06:07+08:00 etcd1 confd[10949]: ERROR "nginx: [emerg] \"upstream\" directive is not allowed here in /tmp/.yourapp.conf196880350:1\nnginx: configuration file /tmp/.yourapp.conf196880350 test failed\n"
2017-05-08T19:06:07+08:00 etcd1 confd[10949]: ERROR Config check failed: exit status 1

原因很简单，注意配置文件中的check_cmd 命令，该命令会进行配置文件检测，检测不通过时，配置文件不会修改，且不会执行后面的reload_cmd命令。这里想不报错也很简单，将配置文件中nginx的配置指向正确的位置，而且让nginx可以正常检测，且检测结果没有错误。再次执行命令，并修改配置文件，会发现有如下信息：

# cat myapp.conf
upstream myapp {
    server 10.0.1.100:80;
    server 10.0.1.101:80;
}
server {
    server_name  myapp.example.com;
    location / {
        proxy_pass        http://myapp;
        proxy_redirect    off;
        proxy_set_header  Host             $host;
        proxy_set_header  X-Real-IP        $remote_addr;
        proxy_set_header  X-Forwarded-For  $proxy_add_x_forwarded_for;
   }
}

三、其他

在模板文件中，会用到一些函数：map、base、exists、get、gets、getenv、datetime等，关于这些函数的使用，可以参看官方文档templates 。

这里再贴下 confd对于模板渲染的语法，貌似没有for这个函数，然后还缺少自定义函数的功能 .

exists

如果这个key在etcd定义了的话？

{{if exists "/key"}}
    value: {{getv "/key"}}
{{end}}

{{if exists "/key"}}
    value: {{getv "/key"}}
{{end}}

get

如果这个key没有，他不会返回一个error

{{with get "/key"}}
    key: {{.Key}}
    value: {{.Value}}
{{end}}

{{with get "/key"}}
    key: {{.Key}}
    value: {{.Value}}
{{end}}

gets

Returns all KVPair, []KVPair, where key matches its argument. Returns an error if key is not found.

{{range gets "/*"}}
    key: {{.Key}}
    value: {{.Value}}
{{end}}

{{range gets "/*"}}
    key: {{.Key}}
    value: {{.Value}}
{{end}}

getv

Returns the value as a string where key matches its argument. Returns an error if key is not found.

value: {{getv "/key"}} 
value: {{getv "/key"}}

getvs

Returns all values, []string, where key matches its argument. Returns an error if key is not found.

{{range getvs "/*"}}
    value: {{.}}
{{end}}

{{range getvs "/*"}}
    value: {{.}}
{{end}}

datetime

Alias for time.Now

# Generated by confd {{datetime}}
# Generated by confd {{datetime}}
Outputs:
# Generated by confd 2015-01-23 13:34:56.093250283 -0800 PST
# Generated by confd 2015-01-23 13:34:56.093250283 -0800 PST
# Generated by confd {datetime.Format("Jan 2, 2006 at 3:04pm (MST)")}
# Generated by confd {datetime.Format("Jan 2, 2006 at 3:04pm (MST)")}
Outputs:
# Generated by confd Jan 23, 2015 at 1:34pm (EST)
# Generated by confd Jan 23, 2015 at 1:34pm (EST)

See the time package for more usage: http://golang.org/pkg/time/

split

可以对于一条数据进行自定义切分，splite

{{ $url := split (getv "/deis/service") ":" }}
    host: {{index $url 0}}
    port: {{index $url 1}}

{{ $url := split (getv "/deis/service") ":" }}
    host: {{index $url 0}}
    port: {{index $url 1}}

json

Returns an map[string]interface{} of the json value.

etcd+confd 基本上可以和任何应用进行组合，如网上比较常见的etcd+confd+nginx 、etcd+confd+haproxy 、etcd+confd+k8s、etcd+confd+tomcat等等。
和tomcat的整合，在官方上也有相应的示例，具体可以参看官方文档tomcat-sample 。

Confd+etcd实现高可用自动发现