Nginx的server为0.0.0.0/0.0.0.1的作用？

看到kong默认的代理和后台server 都是0.0.0.0，代理到上游的服务器proxy_pass $upstream_scheme://kong_upstream;配置如下，

upstream kong_upstream {
    server 0.0.0.1;
    balancer_by_lua_block {
        kong.balancer()
    }
    keepalive 60;
}

监听的IP地址设置了 0.0.0.0 就表示你的nginx服务器监听本机的所有IP地址上,通过任何一个IP地址都可以访问到.
当发送数据的一方还不知道接收方的IP地址时，会在目的IP地址字段中使用0.0.0.0，表示未知IP地址（有时还用于表示无效IP地址）。

• In the Internet Protocol Version 4, the address 0.0.0.0 is a non-routable meta-address used to designate an invalid, unknown or non-applicable target. To give a special meaning to an otherwise invalid piece of data is an application of in-band signaling.

• In the context of servers, 0.0.0.0 means "all IPv4 addresses on the local machine". If a host has two IP addresses, 192.168.1.1 and 10.1.2.1, and a server running on the host listens on 0.0.0.0, it will be reachable at both of those IPs.

• In the context of routing, 0.0.0.0 usually means the default route, i.e. the route which leads to "the rest of" the internet instead of somewhere on the local network.
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