Compatibility with the resolve directive (string length overflow error)

[NicoAdrian]

NGINX open-sourced dynamic DNS resolution one year ago.
However, it looks like lua-upstream-nginx-module is not compatible with this.
When adding resolve (and specifying the zone directive) in an upstream block, calling get_primary_peers results in this error:

lua entry thread aborted: runtime error: string length overflow#012stack traceback:#012coroutine 0:#012#011[C]: in function 'get_primary_peers'#012#011/usr/share/lua/5.1/resty/upstream/healthcheck.lua:845: in function 'status_page'

Example conf:

upstream my_backend {
  zone zone_my_backend 256k;
  server some_server:80 resolve;
  keepalive 128;
}

local hc = require("resty.upstream.healthcheck")
ngx.print(hc.status_page())

I may add that some_server returns 24 different IPs (12 IPv4 and 12 IPv6). Maybe it's too much ? Anyway, it should not crash that way.

[zhuizhuhaomeng]

Thank you for reporting this issue with lua-upstream-nginx-module and NGINX's dynamic DNS resolution.

To better understand and troubleshoot your problem, could you please provide your complete nginx.conf configuration file?
This would help me see the full context of your setup, including any relevant directives that might be affecting this behavior.

[NicoAdrian]

Thank you for your quick response.
I have a dozen of *.conf files so I will try to paste only the relevent parts (some are sensitive):

map $origin $backend {
  default $origin;
  originBad my_backend;

  originA haproxy;
  originB haproxy;
  originC haproxy;
}

upstream haproxy {
  server 127.0.0.1:83;
  keepalive 128;
}



upstream my_backend {
  zone zone_my_backend 256k;
  server some_server:80 resolve;
  keepalive 128;
}

The handler that fails (HTTP 500 and the above error string overflow):

  location = /api/status {
    # No need to log the many systematic internal calls.
    access_log off;
    content_by_lua_block {
      if ngx.var.arg_format == "json" then
        local upstream = require("ngx.upstream")
        local cjson = require("cjson")
        local res = { upstreams = {} }
        local us = upstream.get_upstreams()
        local peers_groups = {
          primary = upstream.get_primary_peers,
          backup = upstream.get_backup_peers
        }

        for _, u in ipairs(us) do
          local statuses = { up = {}, down = {} }
          for group, get_peers in pairs(peers_groups) do
            local ups, downs = {}, {}
            local peers, _ = get_peers(u)
            for _, srv in ipairs(peers) do
              if not srv.down then
                ups[#ups + 1] = srv.name
              else
                downs[#downs + 1] = srv.name
              end
            end
            statuses.up[group] = #ups > 0 and ups or nil
            statuses.down[group] = #downs > 0 and downs or nil
          end
          res.upstreams[u] = statuses
        end
        ngx.header["Content-Type"] = "application/json"
        ngx.print(cjson.encode(res))
      else
        local hc = require("resty.upstream.healthcheck")
        ngx.print(hc.status_page())
      end
    }
  }

proxy_pass http://$backend;

I must say that if I remove the zone directive and the resolve parameter in the my_backend upstream block, it works fine.

[zhuizhuhaomeng]

I need the minimal nginx.conf to reproduce this issue on my side.

[NicoAdrian]

worker_processes  1;

events {
    worker_connections 1024;
}

http {
    upstream backend {
        zone my_zone 256k;
        server google.com:80 resolve;
    }

    resolver 172.50.0.2;

    server {
        listen 80;
        location = /api/status {
          content_by_lua_block {
              local hc = require("resty.upstream.healthcheck")
              ngx.print(hc.status_page())
          }
        }
    }
}

However, If instead of my_server you set for example google.com it will work because it resolves in only one or 2 IPs. Mine resolves into 24

Edit:
Edited the conf file to add google.com as upstream server.

[NicoAdrian]

Nevermind it also crash with google.com .
Comment out zone and remove resolve and it works.

[zhuizhuhaomeng]

The resolve in server google.com:80 resolve is not available in open source nginx before 1.27.3.
The latest supported nginx in openresty is 1.27.1.
So please wait for the new version of openresty.

[NicoAdrian]

The resolve in server google.com:80 resolve is not available in open source nginx before 1.27.3. The latest supported nginx in openresty is 1.27.1. So please wait for the new version of openresty.

Ok, thank you. Is the new version supporting the resolve parameter already planned for release ?

[NicoAdrian]

Hello @zhuizhuhaomeng , any update ?

[zhuizhuhaomeng]

OpenResty 1.29.2.3 has been released

[wuzeyusysu-jpg]

Hello, is OpenResty 1.29.2.3 Fixed this issue?

[wuzeyusysu-jpg]

I use OpenResty 1.29.2.3（nginx version: openresty/1.29.2.3），is still has problem.
server config:
upstream test_backend {
zone test_backend 1m;
server google.com:80 resolve;
}

server {
server_name test.com;
listen 8181;

access_log      logs/access_test.log main buffer=32k;

location ~ ^/(.+) {
    proxy_http_version  1.1;
    proxy_set_header    Connection "";
    proxy_set_header    Host                $host;
    proxy_set_header    X-Forwarded-For     $proxy_add_x_forwarded_for;
    proxy_pass          http://test_backend;
}

location = /upstream {
    content_by_lua_block {
        local cjson = require("cjson")
        local upstream = require "ngx.upstream"
        local get_servers = upstream.get_servers
        local get_upstreams = upstream.get_upstreams
        local get_primary_peers = upstream.get_primary_peers
        local get_backup_peers = upstream.get_backup_peers
        local us = get_upstreams()
        for _, u in ipairs(us) do
          local srvs, err = get_servers(u)
          local ppeers, err = get_primary_peers(u)
          local bpeers, err = get_backup_peers(u)
          local srvsJson = cjson.encode(srvs)
          local ppeersJson = cjson.encode(ppeers)
          local bpeersJson = cjson.encode(bpeers)

          ngx.log(ngx.NOTICE, "upstream ", u, " servers:", srvsJson)
          ngx.log(ngx.NOTICE, "upstream ", u, " primary_peers:", ppeersJson)
          ngx.log(ngx.NOTICE, "upstream ", u, " backup_peers:", bpeersJson)
        end
        ngx.say("OK")
    }
}

}
reload and then request: curl -v test.com/upstream -x 127.0.0.1:8181 , upstream.get_primary_peers only get one addr
[{
"effective_weight": 1,
"conns": 0,
"fails": 0,
"id": 0,
"name": "142.251.167.101:80",
"weight": 1,
"max_fails": 1,
"fail_timeout": 10,
"current_weight": 0
}, {
"effective_weight": 1.4017414851866e+14,
"conns": 18,
"fails": 13,
"accessed": 1.401741485221e+14,
"id": 1,
"name": "",
"weight": 16,
"max_fails": 1,
"fail_timeout": 1,
"current_weight": 0
}, {
"effective_weight": 0,
"conns": 0,
"fails": 0,
"id": 2,
"name": "",
"weight": 0,
"max_fails": 1.4017414851891e+14,
"fail_timeout": 16,
"down": true,
"current_weight": 1.401741485271e+14
}, {
"effective_weight": 0,
"conns": 0,
"fails": 0,
"accessed": 1.4017414852634e+14,
"id": 3,
"checked": 1.4017414852736e+14,
"name": "",
"weight": 0,
"max_fails": 0,
"fail_timeout": 0,
"current_weight": 0
}, {
"effective_weight": 0,
"conns": 0,
"fails": 10,
"id": 4,
"name": "",
"weight": 0,
"max_fails": 0,
"fail_timeout": 0,
"current_weight": 0
}, {
"effective_weight": 13,
"conns": 0,
"fails": 1,
"id": 5,
"name": "",
"weight": 1.4017414852214e+14,
"max_fails": 0,
"fail_timeout": 0,
"down": true,
"current_weight": 1.4017414851955e+14
}]
then i request curl -v test.com/123456 -x 127.0.0.1:8181 and then curl -v test.com/upstream -x 127.0.0.1:8181, worker is coredump
2026/04/14 20:07:15 [notice] 1865464#0: signal 17 (SIGCHLD) received from 1945336
2026/04/14 20:07:15 [alert] 1865464#0: worker process 1945336 exited on signal 11 (core dumped)

#0 hash_sparse_def (seed=5629200477534367745, str=0x1 <error: Cannot access memory at address 0x1>, len=2) at lj_str.c:111
#1 0x00007f7cd9962e8c in lj_str_new (L=0x7f7cd8a397c8, str=0x1 <error: Cannot access memory at address 0x1>, lenx=2) at lj_str.c:355
#2 0x00007f7cd99701ee in lua_pushlstring (L=0x7f7cd8a397c8, str=, len=) at lj_api.c:642
#3 0x00000000005caa60 in ngx_http_lua_get_peer (L=L@entry=0x7f7cd8a397c8, peer=0x7f7cd6546520, id=id@entry=4) at ../ngx_lua_upstream-0.07/src/ngx_http_lua_upstream_module.c:438
#4 0x00000000005cb205 in ngx_http_lua_upstream_get_primary_peers (L=0x7f7cd8a397c8) at ../ngx_lua_upstream-0.07/src/ngx_http_lua_upstream_module.c:281
#5 0x00007f7cd995cd5b in lj_BC_FUNCC () from /usr/local/cdn_backend_ngx/luajit/lib/libluajit-5.1.so.2
#6 0x0000000000596b4b in ngx_http_lua_run_thread (L=L@entry=0x7f7cd8a3a380, r=r@entry=0x7f7cd8635050, ctx=ctx@entry=0x7f7cd8636480, nrets=nrets@entry=0) at ../ngx_lua-0.10.30rc2/src/ngx_http_lua_util.c:1195
#7 0x000000000059ccb0 in ngx_http_lua_content_by_chunk (L=0x7f7cd8a3a380, r=0x7f7cd8635050) at ../ngx_lua-0.10.30rc2/src/ngx_http_lua_contentby.c:124
#8 0x000000000059d1b2 in ngx_http_lua_content_handler (r=0x7f7cd8635050) at ../ngx_lua-0.10.30rc2/src/ngx_http_lua_contentby.c:222
#9 0x00000000004cea1e in ngx_http_core_content_phase (r=0x7f7cd8635050, ph=) at src/http/ngx_http_core_module.c:1285
#10 0x00000000004cd12d in ngx_http_core_run_phases (r=0x7f7cd8635050) at src/http/ngx_http_core_module.c:899
#11 ngx_http_handler (r=r@entry=0x7f7cd8635050) at src/http/ngx_http_core_module.c:882
#12 0x00000000004d4a56 in ngx_http_process_request (r=r@entry=0x7f7cd8635050) at src/http/ngx_http_request.c:2162
#13 0x00000000004d550e in ngx_http_process_request_headers (rev=) at src/http/ngx_http_request.c:1551
#14 0x00000000004d5a3a in ngx_http_process_request_line (rev=0x7f7cd4700e80) at src/http/ngx_http_request.c:1218
#15 0x00000000004a0eab in ngx_epoll_process_events (cycle=, timer=, flags=) at src/event/modules/ngx_epoll_module.c:901
#16 0x0000000000496adb in ngx_process_events_and_timers (cycle=cycle@entry=0x7f7cd8694490) at src/event/ngx_event.c:258
#17 0x000000000049e742 in ngx_worker_process_cycle (cycle=0x7f7cd8694490, data=) at src/os/unix/ngx_process_cycle.c:793
#18 0x000000000049ce1c in ngx_spawn_process (cycle=cycle@entry=0x7f7cd8694490, proc=proc@entry=0x49e6d0 <ngx_worker_process_cycle>, data=data@entry=0x0, name=name@entry=0x84bd80 "worker process", respawn=respawn@entry=-4) at src/os/unix/ngx_process.c:207
#19 0x000000000049efc0 in ngx_start_worker_processes (cycle=cycle@entry=0x7f7cd8694490, n=1, type=type@entry=-4) at src/os/unix/ngx_process_cycle.c:382
#20 0x000000000049f709 in ngx_master_process_cycle (cycle=0x7f7cd8694490, cycle@entry=0x7f7cd868f590) at src/os/unix/ngx_process_cycle.c:241
#21 0x0000000000470bd9 in main (argc=, argv=) at src/core/nginx.c:387

[NicoAdrian]

My worker crashes also. Even simply by calling ngx.print(hc.status_page())

[zhuizhuhaomeng]

PR is welcomed.
Or you can provide a reproducible test to let us resovle it.

[NicoAdrian]

PR is welcomed. Or you can provide a reproducible test to let us resovle it.

worker_processes  1;

events {
    worker_connections 1024;
}

http {
    upstream backend {
        zone my_zone 256k;
        server google.com:80 resolve;
    }

    resolver 172.50.0.2;

    server {
        listen 80;
        location = /api/status {
          content_by_lua_block {
              local hc = require("resty.upstream.healthcheck")
              ngx.print(hc.status_page())
          }
        }
    }
}