zhangguanzhang's Blog

flannel下集群有个节点网络不通的一次排查

kubernetes flannel
字数统计: 1.7k阅读时长: 9 min
2021/08/25

故障

问题和版本没关系，客户的 node 信息啥的后面排错里有。有个节点通信有问题，其余节点都没问题。

排查

惯例信息

先看下 flannel 的 vxlan 的 vtep 信息，客户是双网卡的，但是默认路由是这个网卡，不用管另外的网卡了。下面信息看了下 VtepMAC 和 public-ip 都正常。

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$ kubectl get node -o yaml | grep -B4 public
    annotations:
      flannel.alpha.coreos.com/backend-data: '{"VtepMAC":"76:21:69:41:de:fe"}'
      flannel.alpha.coreos.com/backend-type: vxlan
      flannel.alpha.coreos.com/kube-subnet-manager: "true"
      flannel.alpha.coreos.com/public-ip: 10.25.1.51
--
    annotations:
      flannel.alpha.coreos.com/backend-data: '{"VtepMAC":"b6:61:5c:8d:d9:eb"}'
      flannel.alpha.coreos.com/backend-type: vxlan
      flannel.alpha.coreos.com/kube-subnet-manager: "true"
      flannel.alpha.coreos.com/public-ip: 10.25.1.52
--
    annotations:
      flannel.alpha.coreos.com/backend-data: '{"VtepMAC":"1e:8c:3e:12:fc:0f"}'
      flannel.alpha.coreos.com/backend-type: vxlan
      flannel.alpha.coreos.com/kube-subnet-manager: "true"
      flannel.alpha.coreos.com/public-ip: 10.25.1.53
--
    annotations:
      flannel.alpha.coreos.com/backend-data: '{"VtepMAC":"ba:fe:64:36:6e:a1"}'
      flannel.alpha.coreos.com/backend-type: vxlan
      flannel.alpha.coreos.com/kube-subnet-manager: "true"
      flannel.alpha.coreos.com/public-ip: 10.25.1.54
--
    annotations:
      flannel.alpha.coreos.com/backend-data: '{"VtepMAC":"8e:c1:4d:18:e5:d6"}'
      flannel.alpha.coreos.com/backend-type: vxlan
      flannel.alpha.coreos.com/kube-subnet-manager: "true"
      flannel.alpha.coreos.com/public-ip: 10.25.1.55
--
    annotations:
      flannel.alpha.coreos.com/backend-data: '{"VtepMAC":"fe:95:e6:bf:a0:62"}'
      flannel.alpha.coreos.com/backend-type: vxlan
      flannel.alpha.coreos.com/kube-subnet-manager: "true"
      flannel.alpha.coreos.com/public-ip: 10.25.1.56

coredns 的 pod ip 和 node 分布情况

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$ kubectl -n kube-system get pod -o wide
NAME                                  READY   STATUS    RESTARTS   AGE   IP           NODE         NOMINATED NODE   READINESS GATES
coredns-5757945748-cr67w              1/1     Running   0          19h   172.27.2.7   10.25.1.56   <none>           <none>
coredns-5757945748-krwfd              1/1     Running   0          19h   172.27.1.4   10.25.1.55   <none>           <none>
coredns-5757945748-zf4zm              1/1     Running   0          19h   172.27.3.7   10.25.1.54   <none>           <none>

排查

curl 下 coredns 的 metrics 接口试试，只有 10.25.1.51 和其他节点无法通信。会导致下面的 curl 卡住。

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curl  172.27.1.4:9153

目标机器 10.25.1.55 上通过 flannel.1 接口抓我们的 curl 包:

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$ tcpdump -nn -i flannel.1 host 172.27.1.4 and port 9153 -vv
tcpdump: listening on flannel.1, link-type EN10MB (Ethernet), capture size 262144 bytes
10:07:46.203094 IP (tos 0x0, ttl 64, id 56025, offset 0, flags [DF], proto TCP (6), length 60)
    172.27.0.0.57888 > 172.27.1.4.9153: Flags [S], cksum 0x6804 (correct), seq 879302783, win 28200, options [mss 1410,sackOK,TS val 56279718 ecr 0,nop,wscale 7], length 0
10:07:46.203173 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 60)
    172.27.1.4.9153 > 172.27.0.0.57888: Flags [S.], cksum 0x5969 (incorrect -> 0x163b), seq 4197245653, ack 879302784, win 27960, options [mss 1410,sackOK,TS val 431774697 ecr 56279718,nop,wscale 7], length 0
10:07:47.204797 IP (tos 0x0, ttl 64, id 56026, offset 0, flags [DF], proto TCP (6), length 60)
    172.27.0.0.57888 > 172.27.1.4.9153: Flags [S], cksum 0x641a (correct), seq 879302783, win 28200, options [mss 1410,sackOK,TS val 56280720 ecr 0,nop,wscale 7], length 0
10:07:47.204880 IP (tos 0x0, ttl 63, id 0, offset 0, flags [DF], proto TCP (6), length 60)
    172.27.1.4.9153 > 172.27.0.0.57888: Flags [S.], cksum 0x5969 (incorrect -> 0x1251), seq 4197245653, ack 879302784, win 27960, options [mss 1410,sackOK,TS val 431775699 ecr 56279718,nop,wscale 7], length 0

看着是回复了报文 172.27.1.4.9153 > 172.27.0.0.57888，在我们 curl 的机器 10.25.1.51上 lsof -nPi :57888 看到的确实是卡住的 curl 命令 pid 。10.25.1.51 上也同时抓包看下

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$ tcpdump -nn -i flannel.1 host 172.27.1.4 and port 9153 -vv
tcpdump: listening on flannel.1, link-type EN10MB (Ethernet), capture size 262144 bytes
10:08:57.241129 IP (tos 0x0, ttl 64, id 34444, offset 0, flags [DF], proto TCP (6), length 60)
    172.27.0.0.57966 > 172.27.1.4.9153: Flags [S], cksum 0x5969 (incorrect -> 0x2fb2), seq 276913734, win 28200, options [mss 1410,sackOK,TS val 56350922 ecr 0,nop,wscale 7], length 0
10:08:58.242423 IP (tos 0x0, ttl 64, id 34445, offset 0, flags [DF], proto TCP (6), length 60)
    172.27.0.0.57966 > 172.27.1.4.9153: Flags [S], cksum 0x5969 (incorrect -> 0x2bc8), seq 276913734, win 28200, options [mss 1410,sackOK,TS val 56351924 ecr 0,nop,wscale 7], length 0
10:09:00.246423 IP (tos 0x0, ttl 64, id 34446, offset 0, flags [DF], proto TCP (6), length 60)
    172.27.0.0.57966 > 172.27.1.4.9153: Flags [S], cksum 0x5969 (incorrect -> 0x23f4), seq 276913734, win 28200, options [mss 1410,sackOK,TS val 56353928 ecr 0,nop,wscale 7], length 0

没收到包，从 eth1 抓下 flannel 的 8475 端口(配置里我们改了 flannel 的端口)试试:

目标机器 10.25.1.55 上抓包

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$ tcpdump -nn -i eth1 host 10.25.1.51 and port 8475 -vvv
tcpdump: listening on eth1, link-type EN10MB (Ethernet), capture size 262144 bytes
10:09:40.966705 IP (tos 0x0, ttl 64, id 50110, offset 0, flags [none], proto UDP (17), length 110)
    10.25.1.51.42770 > 10.25.1.55.8475: [no cksum] UDP, length 82
10:09:40.966869 IP (tos 0x0, ttl 64, id 46192, offset 0, flags [none], proto UDP (17), length 110)
    10.25.1.55.48472 > 10.25.1.51.8475: [no cksum] UDP, length 82
10:09:41.968322 IP (tos 0x0, ttl 64, id 50327, offset 0, flags [none], proto UDP (17), length 110)
    10.25.1.51.42770 > 10.25.1.55.8475: [no cksum] UDP, length 82
10:09:41.968440 IP (tos 0x0, ttl 64, id 46957, offset 0, flags [none], proto UDP (17), length 110)
    10.25.1.55.48472 > 10.25.1.51.8475: [no cksum] UDP, length 82
10:09:43.099646 IP (tos 0x0, ttl 64, id 47316, offset 0, flags [none], proto UDP (17), length 110)
    10.25.1.55.48472 > 10.25.1.51.8475: [no cksum] UDP, length 82
10:09:43.972322 IP (tos 0x0, ttl 64, id 51119, offset 0, flags [none], proto UDP (17), length 110)
    10.25.1.51.42770 > 10.25.1.55.8475: [no cksum] UDP, length 82
10:09:43.972454 IP (tos 0x0, ttl 64, id 47934, offset 0, flags [none], proto UDP (17), length 110)
    10.25.1.55.48472 > 10.25.1.51.8475: [no cksum] UDP, length 82
^C

目标机器 10.25.1.51 上抓包:

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$ tcpdump -nn -i eth1 host 10.25.1.55 and port 8475 -vvv
tcpdump: listening on eth1, link-type EN10MB (Ethernet), capture size 262144 bytes
10:10:21.702308 IP (tos 0x0, ttl 64, id 6079, offset 0, flags [none], proto UDP (17), length 110)
    10.25.1.51.59558 > 10.25.1.55.8475: [no cksum] UDP, length 82
10:10:22.702441 IP (tos 0x0, ttl 64, id 6117, offset 0, flags [none], proto UDP (17), length 110)
    10.25.1.51.59558 > 10.25.1.55.8475: [no cksum] UDP, length 82
10:10:24.706444 IP (tos 0x0, ttl 64, id 7699, offset 0, flags [none], proto UDP (17), length 110)
    10.25.1.51.59558 > 10.25.1.55.8475: [no cksum] UDP, length 82

完全没报文过来，看了下 flannel 的接口流量压根就没收到任何包:

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$ ifconfig flannel.1
flannel.1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1450
        inet 172.27.0.0  netmask 255.255.255.255  broadcast 0.0.0.0
        inet6 fe80::7421:69ff:fe41:defe  prefixlen 64  scopeid 0x20<link>
        ether 76:21:69:41:de:fe  txqueuelen 0  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 28900  bytes 2113052 (2.0 MiB)
        TX errors 0  dropped 8 overruns 0  carrier 0  collisions 0

说明报文从 10.25.1.55 发出后没到 51 上，让客户开通 udp 8475 10.25.1.0/24 整个段的东西向安全组后就正常了。

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$ curl  172.27.1.4:9153
^C
$ curl  172.27.1.4:9153
404 page not found

原文作者：Zhangguanzhang

原文链接：http://zhangguanzhang.github.io/2021/08/25/flannel-a-host-net-tmout/

发表日期：August 25th 2021, 3:08:06 pm

更新日期：August 25th 2021, 3:08:06 pm

版权声明：本文采用知识共享署名-非商业性使用 4.0 国际许可协议进行许可

CATALOG
  1. 1. 故障
  2. 2. 排查
    1. 2.1. 惯例信息
    2. 2.2. 排查
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