set_target with hostname fails

[cdowey-r7]

Is there an existing issue for this?

• I have searched the existing issues

Kong version ($ kong version)

3.4.0

Current Behavior

According to the Kong API docs I should be able to call set_target to set the upstream target in my plugin. This does not appear to work unless an IP address is used.

I found this issue which appears to be the same but was recently closed without any specific resolution.

Expected Behavior

Calling set_target with a hostname should work.

Steps To Reproduce

This code fails:

function RedirectTest:access(conf)
  local ok, err1 = kong.service.set_target("example.com", 443)
  if not ok then
      kong.log.err(err1)
      return
  end
end

It results in this error message:

2023/12/13 15:12:11 [error] 69#0: *150 [lua] init.lua:1214: balancer(): failed to set the current peer (address: example.com port: 443): no host allowed while connecting to upstream, client: 127.0.0.1, server: kong, request: "GET / HTTP/1.1", host: "myservice.com"

To verify that DNS resolution is working, I ran this code which works as expected:

local dnsclient = require("resty.dns.client")

function RedirectTest:access(conf)

    local resp, err = dnsclient.resolve("example.com")

    kong.log.debug(">>> IP: ", resp[1].address)
    local ok, err1 = kong.service.set_target(resp[1].address, 443)
    if not ok then
        kong.log.err(err1)
        return
    end
end

I have also checked that DNS resolution works via a shell on the pod.

Anything else?

I am running Kong as a container locally in Docker (on MacOS).

[ADD-SP]

I created an internal ticket (KAG-3500) to track this issue.

[chronolaw]

@chobits , do we have any update about this issue?

[chobits]

hi

This error log was reported by Kong.balancer() , it seems balancer module does not do dns lookup for it, I still need some time to check

---

BTW for your code,

local ok, err1 = kong.service.set_target("example.com", 443)
if not ok then
kong.log.err(err1)
return
end

you dont need to check return value like ok, err1 of kong.service.set_target, this function has no return value, it always successes.

[chobits]

hi, it's a conflict between the doc and its internal impelmentation, currently dns balancer will not actively resolve your setting host. using (KAG-3500) to track it.

Currently your resolved method, using dns_client to resolve it, is ok.

[github-actions]

This issue is marked as stale because it has been open for 14 days with no activity.