[dns] use both RESOLVER and resolver.conf

closes #321

we need to use all nameservers because we can't trust dnsmasq
as it returns the first answer even though it is not the same class

CHANGELOG.md

@@ -10,6 +10,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Support for loading configration from custom URL [PR #323](https://github.com/3scale/apicast/pull/323)
 
+### Changed
+
+- Use `RESOLVER` before falling back to `resolv.conf` [PR #324](https://github.com/3scale/apicast/pull/324)
+
 ## [3.0.0-beta3] - 2017-03-20
 
 ### Changed

apicast/src/resty/resolver.lua

@@ -49,6 +49,18 @@ local function read_resolv_conf(path)
   return output or "", err
 end
 
+local nameserver = {
+  mt = {
+    __tostring = function(t)
+      return concat(t, ':')
+    end
+  }
+}
+
+function nameserver.new(host, port)
+  return setmetatable({ host, port or default_resolver_port }, nameserver.mt)
+end
+
 function _M.parse_nameservers(path)
   local resolv_conf, err = read_resolv_conf(path)
 
@@ -71,26 +83,27 @@ function _M.parse_nameservers(path)
 
   if resolver then
     local m = re.split(resolver, ':', 'oj')
-    insert(nameservers, { m[1] , m[2] or default_resolver_port })
-    return nameservers
+    insert(nameservers, nameserver.new(m[1], m[2]))
+    -- we are going to use all resolvers, because we can't trust dnsmasq
+    -- see https://github.com/3scale/apicast/issues/321 for more details
   end
 
-  for nameserver in gmatch(resolv_conf, 'nameserver%s+([^%s]+)') do
+  for server in gmatch(resolv_conf, 'nameserver%s+([^%s]+)') do
     -- TODO: implement port matching based on https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=549190
-    if nameserver ~= resolver then
-      insert(nameservers, { nameserver, default_resolver_port } )
+    if server ~= resolver then
+      insert(nameservers, nameserver.new(server))
     end
   end
 
   return nameservers
 end
 
-function _M.init_nameservers()
-  local nameservers = _M.parse_nameservers() or {}
+function _M.init_nameservers(path)
+  local nameservers = _M.parse_nameservers(path) or {}
   local search = nameservers.search or {}
 
   for i=1, #nameservers do
-    ngx.log(ngx.INFO, 'adding ', nameservers[i][1],':', nameservers[i][2], ' as default nameserver')
+    ngx.log(ngx.INFO, 'adding ', nameservers[i], ' as default nameserver')
     insert(_M._nameservers, nameservers[i])
   end
 
@@ -114,8 +127,8 @@ function _M.nameservers()
   return _M._nameservers
 end
 
-function _M.init()
-  _M.init_nameservers()
+function _M.init(path)
+  _M.init_nameservers(path)
 end
 
 function _M.new(dns, opts)

t/014-resolver.t

@@ -0,0 +1,45 @@
+use Test::Nginx::Socket 'no_plan';
+use Cwd qw(cwd);
+
+my $pwd = cwd();
+my $apicast = $ENV{TEST_NGINX_APICAST_PATH} || "$pwd/apicast";
+
+$ENV{TEST_NGINX_LUA_PATH} = "$apicast/src/?.lua;;";
+$ENV{TEST_NGINX_HTTP_CONFIG} = "$apicast/http.d/*.conf";
+$ENV{TEST_NGINX_APICAST_PATH} = $apicast;
+$ENV{RESOLVER} = '127.0.1.1:5353';
+
+
+env_to_nginx(
+    'RESOLVER'
+);
+master_on();
+log_level('warn');
+repeat_each(2);
+no_root_location();
+run_tests();
+
+__DATA__
+
+=== TEST 1: uses all resolvers
+both RESOLVER env variable and resolvers in resolv.conf should be used
+--- http_config
+  lua_package_path "$TEST_NGINX_LUA_PATH";
+  init_by_lua_block {
+    require('resty.resolver').init(ngx.config.prefix() .. 'html/resolv.conf')
+  }
+--- config
+  location = /t {
+    content_by_lua_block {
+      local nameservers = require('resty.resolver').nameservers()
+      ngx.say('nameservers: ', #nameservers, ' ', nameservers[1], ' ', nameservers[2], ' ', nameservers[3])
+    }
+  }
+--- request
+GET /t
+--- response_body
+nameservers: 3 127.0.1.15353 1.2.3.453 4.5.6.753
+--- user_files
+>>> resolv.conf
+nameserver 1.2.3.4
+nameserver 4.5.6.7