Docker 服务发现机制的简单实现

nginx.conf

upstream default {
    server 127.0.0.1:12345;

    balancer_by_lua_block {
        local balancer = require "ngx.balancer"
        local ok, err = balancer.set_current_peer(
            ngx.ctx.upstream_host or '127.0.0.1',
            ngx.ctx.upstream_port or 12345
        )

        if not ok then
            ngx.log(ngx.ERR, "failed to set upstream peer: ", err)
            return ngx.exit(ngx.ERR)
        end
    }
}

server {
    listen 127.0.0.1:12345;
    server_name _;
    return 404;
}

server {
    listen 0.0.0.0:443 ssl http2;
    server_name ~(?P<subdomain>[^.]+).example.com;

    client_max_body_size 10M;

    include conf.d/00_ssl.conf;
    ssl_certificate /etc/nginx/ssl/example.com/fullchain.pem;
    ssl_certificate_key /etc/nginx/ssl/example.com/privkey.pem;
    ssl_trusted_certificate /etc/nginx/ssl/example.com/fullchain.pem;

    access_by_lua_file /etc/nginx/conf.d/resolve.lua;

    location / {
        include conf.d/00_proxy.conf;
        proxy_pass http://default;
    }
}

resolve.lua

local resolver = require 'resty.dns.resolver'

local r, err = resolver:new {
    nameservers = {'127.0.0.1'},
    retrans = 5,
    timeout = 2000,
}

if not r then
    ngx.log(ngx.ERR, 'failed to init resolver: ', err)
    return
end

local subdomain = ngx.var.subdomain or 'unknown'
local hostname = subdomain .. '.cluster.local'
local options = {
    qtype = r.TYPE_SRV,
    additional_section = true,
}
local answers, err, tries = r:query(hostname, options, {})

if not answers then
    ngx.log(ngx.ERR, 'failed to query the DNS server: ', hostname, ' ', err)
    return
end

if answers.errcode then
    ngx.log(
        ngx.ERR,
        'failed to query the DNS server: ',
        answers.errcode, ' ', answers.errstr
    )
    return
end

local upstream_host
local upstream_port

for _, answer in ipairs(answers) do
    if not upstream_host then
        if string.match(answer.name or '', '^web-') then
            upstream_host = answer.address
        end
    end

    if not upstream_port then
        if string.match(answer.target or '', '^web-') then
            upstream_port = answer.port
        end
    end

    if upstream_host and upstream_port then
        break
    end
end

ngx.ctx.upstream_host = upstream_host or '127.0.0.1'
ngx.ctx.upstream_port = upstream_port or 12345