feat: add dns discovery

Fix #3517
Signed-off-by: spacewander <spacewanderlzx@gmail.com>

Makefile

@@ -157,6 +157,9 @@ install: default
 	$(INSTALL) -d $(INST_LUADIR)/apisix/core
 	$(INSTALL) apisix/core/*.lua $(INST_LUADIR)/apisix/core/
 
+	$(INSTALL) -d $(INST_LUADIR)/apisix/core/dns
+	$(INSTALL) apisix/core/dns/*.lua $(INST_LUADIR)/apisix/core/dns
+
 	$(INSTALL) -d $(INST_LUADIR)/apisix/cli
 	$(INSTALL) apisix/cli/*.lua $(INST_LUADIR)/apisix/cli/
 

apisix/core.lua

@@ -45,6 +45,7 @@ return {
     timer       = require("apisix.core.timer"),
     id          = require("apisix.core.id"),
     utils       = utils,
+    dns_client  = require("apisix.core.dns.client"),
     etcd        = require("apisix.core.etcd"),
     tablepool   = require("tablepool"),
     empty_tab   = {},

apisix/core/dns/client.lua

@@ -0,0 +1,81 @@
+--
+-- Licensed to the Apache Software Foundation (ASF) under one or more
+-- contributor license agreements.  See the NOTICE file distributed with
+-- this work for additional information regarding copyright ownership.
+-- The ASF licenses this file to You under the Apache License, Version 2.0
+-- (the "License"); you may not use this file except in compliance with
+-- the License.  You may obtain a copy of the License at
+--
+--     http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS,
+-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+-- See the License for the specific language governing permissions and
+-- limitations under the License.
+--
+local require = require
+local log = require("apisix.core.log")
+local json = require("apisix.core.json")
+local table = require("apisix.core.table")
+local math_random = math.random
+local package_loaded = package.loaded
+local setmetatable = setmetatable
+
+
+local _M = {
+    RETURN_RANDOM = 1,
+    RETURN_ALL = 2,
+}
+
+
+function _M.resolve(self, domain, selector)
+    local client = self.client
+
+    -- this function will dereference the CNAME records
+    local answers, err = client.resolve(domain)
+    if not answers then
+        return nil, "failed to query the DNS server: " .. err
+    end
+
+    if answers.errcode then
+        return nil, "server returned error code: " .. answers.errcode
+                    .. ": " .. answers.errstr
+    end
+
+    if selector == _M.RETURN_ALL then
+        log.info("dns resolve ", domain, ", result: ", json.delay_encode(answers))
+        return table.deepcopy(answers)
+    end
+
+    local idx = math_random(1, #answers)
+    local answer = answers[idx]
+    local dns_type = answer.type
+    if dns_type == client.TYPE_A or dns_type == client.TYPE_AAAA then
+        log.info("dns resolve ", domain, ", result: ", json.delay_encode(answer))
+        return table.deepcopy(answer)
+    end
+
+    return nil, "unsupport DNS answer"
+end
+
+
+function _M.new(opts)
+    opts.ipv6 = true
+    opts.timeout = 2000 -- 2 sec
+    opts.retrans = 5 -- 5 retransmissions on receive timeout
+
+    -- make sure each client has its separate room
+    package_loaded["resty.dns.client"] = nil
+    local dns_client_mod = require("resty.dns.client")
+
+    local ok, err = dns_client_mod.init(opts)
+    if not ok then
+        return nil, "failed to init the dns client: " .. err
+    end
+
+    return setmetatable({client = dns_client_mod}, {__index = _M})
+end
+
+
+return _M

apisix/core/utils.lua

@@ -17,16 +17,14 @@
 local config_local   = require("apisix.core.config_local")
 local core_str       = require("apisix.core.string")
 local table          = require("apisix.core.table")
-local json           = require("apisix.core.json")
 local log            = require("apisix.core.log")
 local string         = require("apisix.core.string")
+local dns_client     = require("apisix.core.dns.client")
 local ngx_re         = require("ngx.re")
-local dns_client     = require("resty.dns.client")
 local ipmatcher      = require("resty.ipmatcher")
 local ffi            = require("ffi")
 local base           = require("resty.core.base")
 local open           = io.open
-local math           = math
 local sub_str        = string.sub
 local str_byte       = string.byte
 local tonumber       = tonumber
@@ -43,6 +41,7 @@ local ngx_sleep      = ngx.sleep
 local hostname
 local dns_resolvers
 local current_inited_resolvers
+local current_dns_client
 local max_sleep_interval = 1
 
 ffi.cdef[[
@@ -84,54 +83,33 @@ function _M.split_uri(uri)
 end
 
 
-local function dns_parse(domain)
+local function dns_parse(domain, selector)
     if dns_resolvers ~= current_inited_resolvers then
         local local_conf = config_local.local_conf()
         local valid = table.try_read_attr(local_conf, "apisix", "dns_resolver_valid")
         local enable_resolv_search_opt = table.try_read_attr(local_conf, "apisix",
                                                              "enable_resolv_search_opt")
-
         local opts = {
-            ipv6 = true,
             nameservers = table.clone(dns_resolvers),
-            retrans = 5,  -- 5 retransmissions on receive timeout
-            timeout = 2000,  -- 2 sec
-            order = {"last", "A", "AAAA", "CNAME"}, -- avoid querying SRV (we don't support it yet)
-            validTtl = valid,
+            order = {"last", "A", "AAAA", "CNAME"}, -- avoid querying SRV
         }
 
+        opts.validTtl = valid
+
         if not enable_resolv_search_opt then
             opts.search = {}
         end
 
-        local ok, err = dns_client.init(opts)
-        if not ok then
+        local client, err = dns_client.new(opts)
+        if not client then
             return nil, "failed to init the dns client: " .. err
         end
 
+        current_dns_client = client
         current_inited_resolvers = dns_resolvers
     end
 
-    -- this function will dereference the CNAME records
-    local answers, err = dns_client.resolve(domain)
-    if not answers then
-        return nil, "failed to query the DNS server: " .. err
-    end
-
-    if answers.errcode then
-        return nil, "server returned error code: " .. answers.errcode
-                    .. ": " .. answers.errstr
-    end
-
-    local idx = math.random(1, #answers)
-    local answer = answers[idx]
-    local dns_type = answer.type
-    if dns_type == dns_client.TYPE_A or dns_type == dns_client.TYPE_AAAA then
-        log.info("dns resolve ", domain, ", result: ", json.delay_encode(answer))
-        return table.deepcopy(answer)
-    end
-
-    return nil, "unsupport DNS answer"
+    return current_dns_client:resolve(domain, selector)
 end
 _M.dns_parse = dns_parse
 

apisix/discovery/dns.lua

@@ -0,0 +1,90 @@
+--
+-- Licensed to the Apache Software Foundation (ASF) under one or more
+-- contributor license agreements.  See the NOTICE file distributed with
+-- this work for additional information regarding copyright ownership.
+-- The ASF licenses this file to You under the Apache License, Version 2.0
+-- (the "License"); you may not use this file except in compliance with
+-- the License.  You may obtain a copy of the License at
+--
+--     http://www.apache.org/licenses/LICENSE-2.0
+--
+-- Unless required by applicable law or agreed to in writing, software
+-- distributed under the License is distributed on an "AS IS" BASIS,
+-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+-- See the License for the specific language governing permissions and
+-- limitations under the License.
+--
+
+local core = require("apisix.core")
+local config_local = require("apisix.core.config_local")
+local ipairs = ipairs
+local error = error
+
+
+local dns_client
+local schema = {
+    type = "object",
+    properties = {
+        servers = {
+            type = "array",
+            minItems = 1,
+            items = {
+                type = "string",
+            },
+        },
+    },
+    required = {"servers"}
+}
+
+
+local _M = {}
+
+
+function _M.nodes(service_name)
+    local host, port = core.utils.parse_addr(service_name)
+    core.log.info("discovery dns with host ", host, ", port ", port)
+
+    local records, err = dns_client:resolve(host, core.dns_client.RETURN_ALL)
+    if not records then
+        return nil, err
+    end
+
+    local nodes = core.table.new(#records, 0)
+    for i, r in ipairs(records) do
+        if r.address then
+            nodes[i] = {host = r.address, weight = 1, port = port}
+        end
+    end
+
+    return nodes
+end
+
+
+function _M.init_worker()
+    local local_conf = config_local.local_conf()
+    local ok, err = core.schema.check(schema, local_conf.discovery.dns)
+    if not ok then
+        error("invalid dns discovery configuration: " .. err)
+        return
+    end
+
+    local servers = core.table.try_read_attr(local_conf, "discovery", "dns", "servers")
+
+    local opts = {
+        hosts = {},
+        resolvConf = {},
+        nameservers = servers,
+        order = {"last", "A", "AAAA", "CNAME"}, -- avoid querying SRV (we don't support it yet)
+    }
+
+    local client, err = core.dns_client.new(opts)
+    if not client then
+        error("failed to init the dns client: ", err)
+        return
+    end
+
+    dns_client = client
+end
+
+
+return _M

apisix/upstream.lua

@@ -179,7 +179,12 @@ function _M.set_by_route(route, api_ctx)
         if not dis then
             return 500, "discovery " .. up_conf.discovery_type .. " is uninitialized"
         end
-        local new_nodes = dis.nodes(up_conf.service_name)
+
+        local new_nodes, err = dis.nodes(up_conf.service_name)
+        if not new_nodes then
+            return http_code_upstream_unavailable, "no valid upstream node: " .. err
+        end
+
         local same = upstream_util.compare_upstream_node(up_conf.nodes, new_nodes)
         if not same then
             up_conf.nodes = new_nodes

conf/config-default.yaml

@@ -204,7 +204,10 @@ etcd:
     verify: true                  # whether to verify the etcd endpoint certificate when setup a TLS connection to etcd,
                                   # the default value is true, e.g. the certificate will be verified strictly.
 
-# discovery:                      # service discovery center
+discovery:                        # service discovery center
+#   dns:
+#     resolver:
+#       - "127.0.0.1:8600"        # use the real address of your dns server
 #   eureka:
 #     host:                       # it's possible to define multiple eureka hosts addresses of the same eureka cluster.
 #       - "http://127.0.0.1:8761"

doc/README.md

@@ -33,6 +33,7 @@
 * [Stream Proxy](stream-proxy.md)
 * [gRPC Proxy](grpc-proxy.md)
 * [Customize Nginx Configuration](./customize-nginx-configuration.md)
+* [DNS](./dns.md)
 * [Changelog](../CHANGELOG.md)
 * [Benchmark](benchmark.md)
 * [Code Style](../CODE_STYLE.md)

doc/discovery.md

@@ -21,7 +21,8 @@
 # Integration service discovery registry
 
 * [**Summary**](#summary)
-* [**How extend the discovery client?**](#how-extend-the-discovery-client)
+* [**Supported discovery registries**](#supported-discovery-registries)
+* [**How to extend the discovery client?**](#how-to-extend-the-discovery-client)
     * [**Basic steps**](#basic-steps)
     * [**the example of Eureka**](#the-example-of-eureka)
         * [**Implementation of eureka.lua**](#implementation-of-eurekalua)
@@ -43,7 +44,15 @@ When system traffic changes, the number of servers of the upstream service also
 
 Common registries: Eureka, Etcd, Consul, Zookeeper, Nacos etc.
 
-## How extend the discovery client?
+## Supported discovery registries
+
+Currently we support Eureka and service discovery via DNS, like Consul.
+
+For service discovery via DNS, see [service discovery via DNS](dns.md#service-discovery-via-dns).
+
+For Eureka, see below.
+
+## How to extend the discovery client?
 
 ### Basic steps