roguh · July 31, 2023 22:07 · Jul 31, 2023 · Jul 31, 2023
diff --git a/gistfile1.txt b/gistfile1.txt
@@ -1,4 +1,4 @@
-function _M.resolve_hostname(hostname)
+function resolve_hostname(hostname)
   local dns_resolver_lib = require("resty.dns.resolver")
 
   local dns_resolver, dns_resolver_err = dns_resolver_lib:new({

diff --git a/gistfile1.txt b/gistfile1.txt
@@ -0,0 +1,51 @@
+function _M.resolve_hostname(hostname)
+  local dns_resolver_lib = require("resty.dns.resolver")
+
+  local dns_resolver, dns_resolver_err = dns_resolver_lib:new({
+    -- Kubernetes default nameserver IP
+    -- If your hostnames are public, try Google's DNS nameserver 8.8.8.8
+    nameservers = {"kube-dns.kube-system.svc.cluster.local"},
+    -- 250 milliseconds
+    timeout = 250,
+    retrans = 2
+  })
+
+  if not dns_resolver then
+    ngx.log(
+      ngx.ERR,
+      "Failed to instantiate lua-resty-dns-resolver",
+      dns_resolver_err
+    )
+    return nil
+  end
+
+  local dns_answers, dns_err, dns_tries = dns_resolver:query(hostname, nil, {})
+  if not dns_answers then
+    ngx.log(
+      ngx.ERR,
+      "Failed to query DNS server: ",
+      dns_err,
+      table.concat(dns_tries, "\n  ")
+    )
+    return nil
+  end
+
+  if dns_answers.errcode then
+    ngx.log(
+      ngx.ERR,
+      "DNS server returned error code ",
+      dns_answers.errcode,
+      ": ",
+      dns_answers.errstr
+    )
+    return nil
+  end
+
+  for i, answer in ipairs(dns_answers) do
+    local ip = answer.address or answer.cname
+    if ip ~= nil then
+      return ip
+    end
+  end
+  return nil
+end