Issue description

apisix2.8 dns解析IP变化导致栈溢出复现过程

现象：

​ 服务器500错误

错误日志堆栈 ：

2021/08/30 09:52:15 [error] 10780#10780: *35662 lua entry thread aborted: runtime error: stack overflow
stack traceback:
coroutine 0:
        [C]: in function 'nkeys'
        /usr/local/apisix/apisix/core/table.lua:108: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        /usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
        ..., client: 192.168.33.133, server: _, request: "GET / HTTP/1.1", host: "192.168.33.133:9080"

问题出现状况：

​ 生产环境 cname 对应IP会不定时发生变化

复现过程：

1. apisix 上游服务目标节点配置假cname www.test.com

2. 本机使用 dnsmasq 循环修改 www.test.com 对应的解析IP 127.0.0.1 / 192.168.33.101 (2个即可复现) 并持续访问

    debug 调试日志 dns解析ip在变化
    
    tail -f /usr/local/apisix/logs/error.log | grep "dns resolver domain: www.test.com to"
   2021/08/30 10:45:36 [info] 18176#18176: *51148 [lua] resolver.lua:43: parse_domain(): dns resolver domain: www.test.com to 127.0.0.1, client: 192.168.33.133, server: _, request: "GET / HTTP/1.1", host: "192.168.33.133:9080"
   2021/08/30 10:45:37 [info] 18176#18176: *51161 [lua] resolver.lua:43: parse_domain(): dns resolver domain: www.test.com to 192.168.33.101, client: 192.168.33.133, server: _, request: "GET / HTTP/1.1", host: "192.168.33.133:9080"
   2021/08/30 10:45:37 [info] 18176#18176: *51174 [lua] resolver.lua:43: parse_domain(): dns resolver domain: www.test.com to 127.0.0.1, client: 192.168.33.133, server: _, request: "GET / HTTP/1.1", host: "192.168.33.133:9080"
   2021/08/30 10:45:38 [info] 18176#18176: *51186 [lua] resolver.lua:43: parse_domain(): dns resolver domain: www.test.com to 192.168.33.101, client: 192.168.33.133, server: _, request: "GET / HTTP/1.1", host: "192.168.33.133:9080"
   2021/08/30 10:45:38 [info] 18176#18176: *51200 [lua] resolver.lua:43: parse_domain(): dns resolver domain: www.test.com to 127.0.0.1, client: 192.168.33.133, server: _, request: "GET / HTTP/1.1", host: "192.168.33.133:9080"
   2021/08/30 10:45:39 [info] 18176#18176: *51215 [lua] resolver.lua:43: parse_domain(): dns resolver domain: www.test.com to 192.168.33.101, client: 192.168.33.133, server: _, request: "GET / HTTP/1.1", host: "192.168.33.133:9080"
   

3. 等待一段时间会出现即可复现堆栈、并且内存即将打满

    
    过程中会出现json 过度嵌套导致的 解析错误
    
    json.lua:82: failed to encode: Cannot serialise, excessive nesting (1001) force: true, client: 192.168.33.133, server: _, request: "GET / HTTP/1.1", host: "192.168.33.133:9080"
   2021/08/30 10:47:37 [warn] 18176#18176: *54246 [lua] json.lua:82: failed to encode: Cannot serialise, excessive nesting (1001)
   

相关代码：

parse_domain_in_route.lua

local function parse_domain_in_route(route)
    local nodes = route.value.upstream.nodes
    local new_nodes, err = parse_domain_for_nodes(nodes)   
    if not new_nodes then
        return nil, err
    end

    local up_conf = route.dns_value and route.dns_value.upstream
    local ok = upstream_util.compare_upstream_node(up_conf, new_nodes)
    if ok then
        return route
    end

    -- don't modify the modifiedIndex to avoid plugin cache miss because of DNS resolve result
    -- has changed

    route.dns_value = core.table.deepcopy(route.value)
    route.dns_value.upstream.nodes = new_nodes
    core.log.info("parse route which contain domain: ",
                  core.json.delay_encode(route, true))
    return route
end

Environment

• apisix version (cmd: apisix version):2.8
• OS (cmd: uname -a):
• Linux ip-10-195-19-241.ap-southeast-1.compute.internal 3.10.0-1062.12.1.el7.x86_64 change: added doc of how to load plugin. #1 SMP Tue Feb 4 23:02:59 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
• OpenResty / Nginx version (cmd: nginx -V or openresty -V):
• nginx version: openresty/1.19.3.2
• etcd version, if have (cmd: run curl http://127.0.0.1:9090/v1/server_info to get the info from server-info API):
• {"hostname":"ip-10-195-19-241.ap-southeast-1.compute.internal","version":"2.6","boot_time":1630375405,"etcd_version":"3.4.0","up_time":4503,"last_report_time":1630379905,"id":"a2315b76-470d-4457-8625-f943ff24eac8"}
• apisix-dashboard version, if have:
• luarocks version, if the issue is about installation (cmd: luarocks --version):

Steps to reproduce

复现过程：

1. apisix 上游服务目标节点配置假cname www.test.com

2. 本机使用 dnsmasq 循环修改 www.test.com 对应的解析IP 127.0.0.1 / 192.168.33.101 (2个即可复现) 并持续访问

    debug 调试日志 dns解析ip在变化
    
    tail -f /usr/local/apisix/logs/error.log | grep "dns resolver domain: www.test.com to"
   2021/08/30 10:45:36 [info] 18176#18176: *51148 [lua] resolver.lua:43: parse_domain(): dns resolver domain: www.test.com to 127.0.0.1, client: 192.168.33.133, server: _, request: "GET / HTTP/1.1", host: "192.168.33.133:9080"
   2021/08/30 10:45:37 [info] 18176#18176: *51161 [lua] resolver.lua:43: parse_domain(): dns resolver domain: www.test.com to 192.168.33.101, client: 192.168.33.133, server: _, request: "GET / HTTP/1.1", host: "192.168.33.133:9080"
   2021/08/30 10:45:37 [info] 18176#18176: *51174 [lua] resolver.lua:43: parse_domain(): dns resolver domain: www.test.com to 127.0.0.1, client: 192.168.33.133, server: _, request: "GET / HTTP/1.1", host: "192.168.33.133:9080"
   2021/08/30 10:45:38 [info] 18176#18176: *51186 [lua] resolver.lua:43: parse_domain(): dns resolver domain: www.test.com to 192.168.33.101, client: 192.168.33.133, server: _, request: "GET / HTTP/1.1", host: "192.168.33.133:9080"
   2021/08/30 10:45:38 [info] 18176#18176: *51200 [lua] resolver.lua:43: parse_domain(): dns resolver domain: www.test.com to 127.0.0.1, client: 192.168.33.133, server: _, request: "GET / HTTP/1.1", host: "192.168.33.133:9080"
   2021/08/30 10:45:39 [info] 18176#18176: *51215 [lua] resolver.lua:43: parse_domain(): dns resolver domain: www.test.com to 192.168.33.101, client: 192.168.33.133, server: _, request: "GET / HTTP/1.1", host: "192.168.33.133:9080"
   

3. 等待一段时间会出现即可复现堆栈、并且内存即将打满

Actual result

apisix 500错误 table拷贝递归栈溢出

Error log

2021/08/30 09:52:15 [error] 10780#10780: *35662 lua entry thread aborted: runtime error: stack overflow
stack traceback:
coroutine 0:
[C]: in function 'nkeys'
/usr/local/apisix/apisix/core/table.lua:108: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
/usr/local/apisix/apisix/core/table.lua:111: in function '_deepcopy'
..., client: 192.168.33.133, server: _, request: "GET / HTTP/1.1", host: "192.168.33.133:9080"

### Expected result

dns解析变化导致栈溢出