CoreDNS域名解析问题

神洲 · 發表於 2022-5-19 20:34:00

使用场景

平台组件部署模式及选型

网络插件：Calico（非BGP协议，使用Calico IPIP tunl模式）
Coredns：部署在平台集群中，非（hostNetwork: true）模式；Coredns的POD与跨node通信使用IPIP tunl

kube-proxy：使用默认的iptables NAT方式，减少一步内核态到用户态的切换

data:
  config.conf: |-
    apiVersion: kubeproxy.config.k8s.io/v1alpha1
    bindAddress: 0.0.0.0
    clientConnection:
      acceptContentTypes: ""
      burst: 0
      contentType: ""
      kubeconfig: /var/lib/kube-proxy/kubeconfig.conf
      qps: 0
    clusterCIDR: 172.19.0.0/16
    configSyncPeriod: 0s
    conntrack:
      maxPerCore: null
      min: null
      tcpCloseWaitTimeout: null
      tcpEstablishedTimeout: null
    detectLocalMode: ""
    enableProfiling: false
    healthzBindAddress: ""
    hostnameOverride: ""
    iptables:
      masqueradeAll: false
      masqueradeBit: null
      minSyncPeriod: 0s
      syncPeriod: 0s
    ipvs:
      excludeCIDRs: null
      minSyncPeriod: 0s
      scheduler: ""
      strictARP: false
      syncPeriod: 0s
      tcpFinTimeout: 0s
      tcpTimeout: 0s
      udpTimeout: 0s
    kind: KubeProxyConfiguration
    metricsBindAddress: ""
    mode: ""
    nodePortAddresses: null
    oomScoreAdj: null
    portRange: ""
    showHiddenMetricsForVersion: ""
    udpIdleTimeout: 0s
    winkernel:
      enableDSR: false
      networkName: ""
      sourceVip: ""

DNS服务器：
coredns： Coredns1/2(nflow.so)平台集群内部DNS服务器，主要作用用来解决平台集群中的service/pod域名解析，使用协议53/TCP 53/UDP
内部DNS：（DNS1/DNS2 nflow.internal) 主要作用，解析阿里云CNAME 及内部基础组件系统（zk/mq/xxl-job/amq） 使用协议 53/UDP

故障描述

部署的应用容器在请求内部域名时（redis.dev02.nflow.internal）无法被解析，具体报警日志如下

[2020-08-24 11:36:18.721] [DubboServerHandler-172.19.25.116:20012-thread-997] [Careful] [ERROR] [traceId-xincheng-flow-cce7124074414c82a2cb8a51be8a8e53_202008241134119950889D95AEC6A5] - register exception:
org.springframework.data.redis.RedisConnectionFailureException: Cannot get Jedis connection; nested exception is redis.clients.jedis.exceptions.JedisConnectionException: Could not get a resource from the pool
    at org.springframework.data.redis.connection.jedis.JedisConnectionFactory.fetchJedisConnector(JedisConnectionFactory.java:162)
    at org.springframework.data.redis.connection.jedis.JedisConnectionFactory.getConnection(JedisConnectionFactory.java:251)
    at org.springframework.data.redis.connection.jedis.JedisConnectionFactory.getConnection(JedisConnectionFactory.java:58)
    at org.springframework.data.redis.core.RedisConnectionUtils.doGetConnection(RedisConnectionUtils.java:128)
    at org.springframework.data.redis.core.RedisConnectionUtils.getConnection(RedisConnectionUtils.java:91)
    at org.springframework.data.redis.core.RedisConnectionUtils.getConnection(RedisConnectionUtils.java:78)
    at org.springframework.data.redis.core.RedisTemplate.execute(RedisTemplate.java:178)
    at org.springframework.data.redis.core.RedisTemplate.execute(RedisTemplate.java:153)
    at org.springframework.data.redis.core.AbstractOperations.execute(AbstractOperations.java:86)
    at org.springframework.data.redis.core.DefaultValueOperations.setIfAbsent(DefaultValueOperations.java:216)
    at com.weishang.redis.lock.RedisLockBaseArithmetic.lock(RedisLockBaseArithmetic.java:67)
    at com.weishang.user.service.impl.UserServiceImpl.register(UserServiceImpl.java:639)
    at com.weishang.user.service.impl.UserServiceImpl.registerWithoutCode(UserServiceImpl.java:792)
    at com.alibaba.dubbo.common.bytecode.Wrapper58.invokeMethod(Wrapper58.java)
    at com.alibaba.dubbo.rpc.proxy.javassist.JavassistProxyFactory$1.doInvoke(JavassistProxyFactory.java:47)
    at com.alibaba.dubbo.rpc.proxy.AbstractProxyInvoker.invoke(AbstractProxyInvoker.java:76)
    at com.alibaba.dubbo.config.invoker.DelegateProviderMetaDataInvoker.invoke(DelegateProviderMetaDataInvoker.java:52)
    at com.alibaba.dubbo.rpc.protocol.InvokerWrapper.invoke(InvokerWrapper.java:56)
    at com.weishang.framework.dubbo.filter.log.LogTraceProviderFilter.invoke(LogTraceProviderFilter.java:25)
    at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72)
    at com.alibaba.dubbo.rpc.filter.ExceptionFilter.invoke(ExceptionFilter.java:62)
    at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72)
    at com.alibaba.dubbo.monitor.support.MonitorFilter.invoke(MonitorFilter.java:75)
    at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72)
    at com.alibaba.dubbo.rpc.filter.TimeoutFilter.invoke(TimeoutFilter.java:42)
    at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72)
    at com.alibaba.dubbo.rpc.protocol.dubbo.filter.TraceFilter.invoke(TraceFilter.java:78)
    at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72)
    at com.alibaba.dubbo.rpc.filter.ContextFilter.invoke(ContextFilter.java:73)
    at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72)
    at com.alibaba.dubbo.rpc.filter.GenericFilter.invoke(GenericFilter.java:141)
    at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72)
    at com.alibaba.dubbo.rpc.filter.ClassLoaderFilter.invoke(ClassLoaderFilter.java:38)
    at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72)
    at com.alibaba.dubbo.rpc.filter.EchoFilter.invoke(EchoFilter.java:38)
    at com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper$1.invoke(ProtocolFilterWrapper.java:72)
    at com.alibaba.dubbo.rpc.protocol.dubbo.DubboProtocol$1.reply(DubboProtocol.java:104)
    at com.alibaba.dubbo.remoting.exchange.support.header.HeaderExchangeHandler.handleRequest(HeaderExchangeHandler.java:96)
    at com.alibaba.dubbo.remoting.exchange.support.header.HeaderExchangeHandler.received(HeaderExchangeHandler.java:173)
    at com.alibaba.dubbo.remoting.transport.DecodeHandler.received(DecodeHandler.java:51)
    at com.alibaba.dubbo.remoting.transport.dispatcher.ChannelEventRunnable.run(ChannelEventRunnable.java:57)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)
Caused by: redis.clients.jedis.exceptions.JedisConnectionException: Could not get a resource from the pool
    at redis.clients.util.Pool.getResource(Pool.java:50)
    at redis.clients.jedis.JedisPool.getResource(JedisPool.java:99)
    at redis.clients.jedis.JedisPool.getResource(JedisPool.java:12)
    at org.springframework.data.redis.connection.jedis.JedisConnectionFactory.fetchJedisConnector(JedisConnectionFactory.java:155)
    ... 43 more
Caused by: redis.clients.jedis.exceptions.JedisConnectionException: java.net.UnknownHostException: redis.dev02.nflow.internal
    at redis.clients.jedis.Connection.connect(Connection.java:164)
    at redis.clients.jedis.BinaryClient.connect(BinaryClient.java:82)
    at redis.clients.jedis.BinaryJedis.connect(BinaryJedis.java:1641)
    at redis.clients.jedis.JedisFactory.makeObject(JedisFactory.java:85)
    at org.apache.commons.pool2.impl.GenericObjectPool.create(GenericObjectPool.java:861)
    at org.apache.commons.pool2.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:435)
    at org.apache.commons.pool2.impl.GenericObjectPool.borrowObject(GenericObjectPool.java:363)
    at redis.clients.util.Pool.getResource(Pool.java:48)
    ... 46 more
Caused by: java.net.UnknownHostException: redis.dev02.nflow.internal
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:196)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:394)
    at java.net.Socket.connect(Socket.java:606)
    at redis.clients.jedis.Connection.connect(Connection.java:158)
    ... 53 more

故障分析

排查此故障过程如下切换至应用环境Pod容器中

[root@dev02-xc-admin-5c768555-jgxhq nflow]# host -v  redis.dev02.nflow.internal
Trying "redis.dev02.nflow.internal.dev.svc.nflow.so"
Trying "redis.dev02.nflow.internal.svc.nflow.so"
Trying "redis.dev02.nflow.internal.nflow.so"
Trying "redis.dev02.nflow.internal"
Trying "redis.dev02.nflow.internal"

发现如上的故障现象，是由于应用Pod容器请求corndns使用的是TCP协议，由于corndns的ServiceIP只暴露了UDP协议，默认TCP是enable，由于考虑到域名解析时，TCP消耗资源及效率低的原因，故将TCP相关配置delete操作
```
spec:
  ports:
    - name: dns
      protocol: UDP
      port: 53
      targetPort: 53
    - name: metrics
      protocol: TCP
      port: 9153
      targetPort: 9153
```

于是将corndns的service配置开启TCP协议

ports:
    - name: dns
      protocol: UDP
      port: 53
      targetPort: 53
    - name: dns-tcp
      protocol: TCP
      port: 53
      targetPort: 53
    - name: metrics
      protocol: TCP
      port: 9153
      targetPort: 9153

再次查看域名解析结果

[root@dev02-xc-admin-5c768555-jgxhq nflow]# host -v  redis.dev02.nflow.internal
Trying "redis.dev02.nflow.internal.dev.svc.nflow.so"
Trying "redis.dev02.nflow.internal.svc.nflow.so"
Trying "redis.dev02.nflow.internal.nflow.so"
Trying "redis.dev02.nflow.internal"
Trying "redis.dev02.nflow.internal"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 15914
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 13, ADDITIONAL: 22
 
;; QUESTION SECTION:
;redis.dev02.nflow.internal.    IN  A
 
;; ANSWER SECTION:
redis.dev02.nflow.internal. 9   IN  CNAME   r-bp1qv8wuvhbs9k8kk8.redis.rds.aliyuncs.com.
r-bp1qv8wuvhbs9k8kk8.redis.rds.aliyuncs.com. 9 IN A 10.1.35.155
 
;; AUTHORITY SECTION:
com.            9   IN  NS  c.gtld-servers.net.
com.            9   IN  NS  a.gtld-servers.net.
com.            9   IN  NS  k.gtld-servers.net.
com.            9   IN  NS  d.gtld-servers.net.
com.            9   IN  NS  b.gtld-servers.net.
com.            9   IN  NS  j.gtld-servers.net.
com.            9   IN  NS  h.gtld-servers.net.
com.            9   IN  NS  f.gtld-servers.net.
com.            9   IN  NS  i.gtld-servers.net.
com.            9   IN  NS  g.gtld-servers.net.
com.            9   IN  NS  l.gtld-servers.net.
com.            9   IN  NS  m.gtld-servers.net.
com.            9   IN  NS  e.gtld-servers.net.
 
;; ADDITIONAL SECTION:
e.gtld-servers.net. 9   IN  A   192.12.94.30
b.gtld-servers.net. 9   IN  A   192.33.14.30
j.gtld-servers.net. 9   IN  A   192.48.79.30
j.gtld-servers.net. 9   IN  AAAA    2001:502:7094::30
m.gtld-servers.net. 9   IN  A   192.55.83.30
m.gtld-servers.net. 9   IN  AAAA    2001:501:b1f9::30
i.gtld-servers.net. 9   IN  A   192.43.172.30
i.gtld-servers.net. 9   IN  AAAA    2001:503:39c1::30
f.gtld-servers.net. 9   IN  AAAA    2001:503:d414::30
a.gtld-servers.net. 9   IN  A   192.5.6.30
g.gtld-servers.net. 9   IN  A   192.42.93.30
g.gtld-servers.net. 9   IN  AAAA    2001:503:eea3::30
h.gtld-servers.net. 9   IN  A   192.54.112.30
h.gtld-servers.net. 9   IN  AAAA    2001:502:8cc::30
l.gtld-servers.net. 9   IN  A   192.41.162.30
l.gtld-servers.net. 9   IN  AAAA    2001:500:d937::30
k.gtld-servers.net. 9   IN  A   192.52.178.30
k.gtld-servers.net. 9   IN  AAAA    2001:503:d2d::30
c.gtld-servers.net. 9   IN  A   192.26.92.30
c.gtld-servers.net. 9   IN  AAAA    2001:503:83eb::30
d.gtld-servers.net. 9   IN  A   192.31.80.30
d.gtld-servers.net. 9   IN  AAAA    2001:500:856e::30
 
Received 1509 bytes from 10.10.0.10#53 in 0 ms
Trying "r-bp1qv8wuvhbs9k8kk8.redis.rds.aliyuncs.com"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55554
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
 
;; QUESTION SECTION:
;r-bp1qv8wuvhbs9k8kk8.redis.rds.aliyuncs.com. IN    AAAA
 
;; AUTHORITY SECTION:
rds.aliyuncs.com.   30  IN  SOA hidden-master.aliyun.com. hostmaster.aliyun-inc.com. 2046235511 7200 900 2592000 600
 
Received 162 bytes from 10.10.0.10#53 in 0 ms
Trying "r-bp1qv8wuvhbs9k8kk8.redis.rds.aliyuncs.com"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 3305
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
 
;; QUESTION SECTION:
;r-bp1qv8wuvhbs9k8kk8.redis.rds.aliyuncs.com. IN    MX
 
;; AUTHORITY SECTION:
rds.aliyuncs.com.   30  IN  SOA hidden-master.aliyun.com. hostmaster.aliyun-inc.com. 2046235511 7200 900 2592000 600
 
Received 162 bytes from 10.10.0.10#53 in 0 ms
 
虽然仍然还是time_wait的状态，但是可以解析成功，且应用没有报错，请求域名解析超时的错

Corndns相关调整

配置清单

nflow.internal	只负责Pod内部请求nflow.internal的域名直接响应，并转发给内部DNS(10.1.1.132)
.:53	负责匹配非nflow.internal及Kubernetes内部域名及外部域名解析，其中承载外部域名解析时，直接forward到Pod所有的node节点上的/etc/resolv.conf定义的nameserver的地址

在cronfile中新增一个SOA，配置如下

{
    "Corefile": "nflow.internal:53 {
            errors
            cache 10
            forward . 10.1.1.133 {
              prefer_udp
            }
            reload
        }
        .:53 {
            errors
            health {
               lameduck 5s
            }
            ready
            kubernetes nflow.so in-addr.arpa ip6.arpa {
               pods insecure
               fallthrough in-addr.arpa ip6.arpa
               ttl 30
            }
            prometheus :9153
            forward . /etc/resolv.conf
            cache 30
            loop
            reload
            loadbalance
        }
        "
}

根据以上配置可以得出如下结果
- 需要解析nflow.internal域名直接匹配nflow.internal并直接forward给10.1.1.132上游DNS服务器（相对coredns）
- 需要解析非nflow.internal域名及Kubernetes平台内部的svc/pod域名时及外部域名则匹配默认（.:53）SOA，这样的好处：
  
  节省了如果需要解析nflow.internal需要遍历整个Kubernetes 默认的SOA（namespace.svc.nflow.so/svc.nflow.so/nflow.so）
  
  节省了如果请求外部域名解析时向内部DNS转发的压力

依照上面优化建议配置，需要调整相关Pod的dnsPolicy配置，如下

dnsPolicy: None
dnsConfig:
  nameservers:
    - 10.10.0.10
  options:
    - name: ndots
      value: '2'

调整后解析结果如下

### baidu.com ###
[root@dev02-xc-user-6f6c5876bf-8vcr4 nflow]# host -v www.baidu.com
Trying "www.baidu.com"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50799
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0
 
;; QUESTION SECTION:
;www.baidu.com.         IN  A
 
;; ANSWER SECTION:
www.baidu.com.      30  IN  CNAME   www.a.shifen.com.
www.a.shifen.com.   30  IN  A   180.101.49.11
www.a.shifen.com.   30  IN  A   180.101.49.12
 
Received 138 bytes from 10.10.0.10#53 in 1 ms
Trying "www.a.shifen.com"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62483
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
 
;; QUESTION SECTION:
;www.a.shifen.com.      IN  AAAA
 
;; AUTHORITY SECTION:
a.shifen.com.       30  IN  SOA ns1.a.shifen.com. baidu_dns_master.baidu.com. 2008240002 5 5 2592000 3600
 
Received 124 bytes from 10.10.0.10#53 in 0 ms
Trying "www.a.shifen.com"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 62962
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
 
;; QUESTION SECTION:
;www.a.shifen.com.      IN  MX
 
;; AUTHORITY SECTION:
a.shifen.com.       26  IN  SOA ns1.a.shifen.com. baidu_dns_master.baidu.com. 2008240001 5 5 2592000 3600
 
Received 124 bytes from 10.10.0.10#53 in 0 ms
[root@dev02-xc-user-6f6c5876bf-8vcr4 nflow]#
[root@dev02-xc-user-6f6c5876bf-8vcr4 nflow]# host -v www.baidu.com
Trying "www.baidu.com"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 56964
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0
 
;; QUESTION SECTION:
;www.baidu.com.         IN  A
 
;; ANSWER SECTION:
www.baidu.com.      30  IN  CNAME   www.a.shifen.com.
www.a.shifen.com.   30  IN  A   180.101.49.11
www.a.shifen.com.   30  IN  A   180.101.49.12
 
Received 138 bytes from 10.10.0.10#53 in 1 ms
Trying "www.a.shifen.com"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 53138
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
 
;; QUESTION SECTION:
;www.a.shifen.com.      IN  AAAA
 
;; AUTHORITY SECTION:
a.shifen.com.       30  IN  SOA ns1.a.shifen.com. baidu_dns_master.baidu.com. 2008240002 5 5 2592000 3600
 
Received 124 bytes from 10.10.0.10#53 in 0 ms
Trying "www.a.shifen.com"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 59658
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
 
;; QUESTION SECTION:
;www.a.shifen.com.      IN  MX
 
;; AUTHORITY SECTION:
a.shifen.com.       30  IN  SOA ns1.a.shifen.com. baidu_dns_master.baidu.com. 2008240002 5 5 2592000 3600
 
Received 124 bytes from 10.10.0.10#53 in 0 ms
 
 
### nflow.internal ###
[root@dev02-xc-user-6f6c5876bf-8vcr4 nflow]# host -v redis.dev01.nflow.internal
Trying "redis.dev01.nflow.internal"
Trying "redis.dev01.nflow.internal"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 10518
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 13, ADDITIONAL: 21
 
;; QUESTION SECTION:
;redis.dev01.nflow.internal.    IN  A
 
;; ANSWER SECTION:
redis.dev01.nflow.internal. 5   IN  CNAME   r-bp1yy77dfyewep8jzf.redis.rds.aliyuncs.com.
r-bp1yy77dfyewep8jzf.redis.rds.aliyuncs.com. 5 IN A 10.1.32.111
 
;; AUTHORITY SECTION:
com.            5   IN  NS  b.gtld-servers.net.
com.            5   IN  NS  c.gtld-servers.net.
com.            5   IN  NS  f.gtld-servers.net.
com.            5   IN  NS  h.gtld-servers.net.
com.            5   IN  NS  m.gtld-servers.net.
com.            5   IN  NS  d.gtld-servers.net.
com.            5   IN  NS  i.gtld-servers.net.
com.            5   IN  NS  e.gtld-servers.net.
com.            5   IN  NS  j.gtld-servers.net.
com.            5   IN  NS  k.gtld-servers.net.
com.            5   IN  NS  a.gtld-servers.net.
com.            5   IN  NS  l.gtld-servers.net.
com.            5   IN  NS  g.gtld-servers.net.
 
;; ADDITIONAL SECTION:
e.gtld-servers.net. 5   IN  A   192.12.94.30
b.gtld-servers.net. 5   IN  A   192.33.14.30
j.gtld-servers.net. 5   IN  A   192.48.79.30
j.gtld-servers.net. 5   IN  AAAA    2001:502:7094::30
m.gtld-servers.net. 5   IN  A   192.55.83.30
m.gtld-servers.net. 5   IN  AAAA    2001:501:b1f9::30
i.gtld-servers.net. 5   IN  A   192.43.172.30
i.gtld-servers.net. 5   IN  AAAA    2001:503:39c1::30
f.gtld-servers.net. 5   IN  AAAA    2001:503:d414::30
a.gtld-servers.net. 5   IN  A   192.5.6.30
g.gtld-servers.net. 5   IN  A   192.42.93.30
g.gtld-servers.net. 5   IN  AAAA    2001:503:eea3::30
h.gtld-servers.net. 5   IN  A   192.54.112.30
h.gtld-servers.net. 5   IN  AAAA    2001:502:8cc::30
l.gtld-servers.net. 5   IN  AAAA    2001:500:d937::30
k.gtld-servers.net. 5   IN  A   192.52.178.30
k.gtld-servers.net. 5   IN  AAAA    2001:503:d2d::30
c.gtld-servers.net. 5   IN  A   192.26.92.30
c.gtld-servers.net. 5   IN  AAAA    2001:503:83eb::30
d.gtld-servers.net. 5   IN  A   192.31.80.30
d.gtld-servers.net. 5   IN  AAAA    2001:500:856e::30
 
Received 1475 bytes from 10.10.0.10#53 in 0 ms
Trying "r-bp1yy77dfyewep8jzf.redis.rds.aliyuncs.com"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 16727
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
 
;; QUESTION SECTION:
;r-bp1yy77dfyewep8jzf.redis.rds.aliyuncs.com. IN    AAAA
 
;; AUTHORITY SECTION:
rds.aliyuncs.com.   30  IN  SOA hidden-master.aliyun.com. hostmaster.aliyun-inc.com. 2046235958 7200 900 2592000 600
 
Received 162 bytes from 10.10.0.10#53 in 0 ms
Trying "r-bp1yy77dfyewep8jzf.redis.rds.aliyuncs.com"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 35921
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
 
;; QUESTION SECTION:
;r-bp1yy77dfyewep8jzf.redis.rds.aliyuncs.com. IN    MX
 
;; AUTHORITY SECTION:
rds.aliyuncs.com.   30  IN  SOA hidden-master.aliyun.com. hostmaster.aliyun-inc.com. 2046235958 7200 900 2592000 600
 
Received 162 bytes from 10.10.0.10#53 in 0 ms
 
 
### nflow.so ###
[root@dev02-xc-user-6f6c5876bf-8vcr4 nflow]# host -v sit-xc-job.sit.svc.nflow.so
Trying "sit-xc-job.sit.svc.nflow.so"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 52666
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
 
;; QUESTION SECTION:
;sit-xc-job.sit.svc.nflow.so.   IN  A
 
;; ANSWER SECTION:
sit-xc-job.sit.svc.nflow.so. 30 IN  A   10.10.207.12
 
Received 88 bytes from 10.10.0.10#53 in 0 ms
Trying "sit-xc-job.sit.svc.nflow.so"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 34898
;; flags: qr aa rd; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
 
;; QUESTION SECTION:
;sit-xc-job.sit.svc.nflow.so.   IN  AAAA
 
;; AUTHORITY SECTION:
nflow.so.       30  IN  SOA ns.dns.nflow.so. hostmaster.nflow.so. 1598246184 7200 1800 86400 30
 
Received 123 bytes from 10.10.0.10#53 in 0 ms
Trying "sit-xc-job.sit.svc.nflow.so"
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 54241
;; flags: qr aa rd; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
 
;; QUESTION SECTION:
;sit-xc-job.sit.svc.nflow.so.   IN  MX
 
;; AUTHORITY SECTION:
nflow.so.       30  IN  SOA ns.dns.nflow.so. hostmaster.nflow.so. 1598246184 7200 1800 86400 30
 
Received 123 bytes from 10.10.0.10#53 in 0 ms

来源：https://www.cnblogs.com/apink/p/16290019.html