Kubernetes K8S在IPVS代理模式下Service服务的ClusterIP类型访问失败处理

发表于 | 分类于 ， | | 阅读次数:
字数统计: 1.8k | 阅读时长 ≈ 9

image

Kubernetes K8S使用IPVS代理模式，当Service的类型为ClusterIP时，如何处理访问service却不能访问后端pod的情况。

背景现象

Kubernetes K8S使用IPVS代理模式，当Service的类型为ClusterIP时，出现访问service却不能访问后端pod的情况。

主机配置规划

服务器名称(hostname) 系统版本 配置 内网IP 外网IP(模拟)
k8s-master CentOS7.7 2C/4G/20G 172.16.1.110 10.0.0.110
k8s-node01 CentOS7.7 2C/4G/20G 172.16.1.111 10.0.0.111
k8s-node02 CentOS7.7 2C/4G/20G 172.16.1.112 10.0.0.112

场景复现

Deployment的yaml信息

yaml文件

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
[root@k8s-master service]# pwd
/root/k8s_practice/service
[root@k8s-master service]# cat myapp-deploy.yaml 
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp-deploy
  namespace: default
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myapp
      release: v1
  template:
    metadata:
      labels:
        app: myapp
        release: v1
        env: test
    spec:
      containers:
      - name: myapp
        image: registry.cn-beijing.aliyuncs.com/google_registry/myapp:v1
        imagePullPolicy: IfNotPresent
        ports:
        - name: http
          containerPort: 80

启动Deployment并查看状态

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
[root@k8s-master service]# kubectl apply -f myapp-deploy.yaml 
deployment.apps/myapp-deploy created
[root@k8s-master service]# 
[root@k8s-master service]# kubectl get deploy -o wide
NAME           READY   UP-TO-DATE   AVAILABLE   AGE   CONTAINERS   IMAGES                                                      SELECTOR
myapp-deploy   3/3     3            3           14s   myapp        registry.cn-beijing.aliyuncs.com/google_registry/myapp:v1   app=myapp,release=v1
[root@k8s-master service]# kubectl get rs -o wide
NAME                      DESIRED   CURRENT   READY   AGE   CONTAINERS   IMAGES                                                      SELECTOR
myapp-deploy-5695bb5658   3         3         3       21s   myapp        registry.cn-beijing.aliyuncs.com/google_registry/myapp:v1   app=myapp,pod-template-hash=5695bb5658,release=v1
[root@k8s-master service]#
[root@k8s-master service]# kubectl get pod -o wide --show-labels
NAME                            READY   STATUS    RESTARTS   AGE     IP             NODE         NOMINATED NODE   READINESS GATES   LABELS
myapp-deploy-5695bb5658-7tgfx   1/1     Running   0          39s     10.244.2.111   k8s-node02   <none>           <none>            app=myapp,env=test,pod-template-hash=5695bb5658,release=v1
myapp-deploy-5695bb5658-95zxm   1/1     Running   0          39s     10.244.3.165   k8s-node01   <none>           <none>            app=myapp,env=test,pod-template-hash=5695bb5658,release=v1
myapp-deploy-5695bb5658-xtxbp   1/1     Running   0          39s     10.244.3.164   k8s-node01   <none>           <none>            app=myapp,env=test,pod-template-hash=5695bb5658,release=v1

curl访问

1
2
3
4
5
6
7
8
[root@k8s-master service]# curl 10.244.2.111/hostname.html
myapp-deploy-5695bb5658-7tgfx
[root@k8s-master service]# 
[root@k8s-master service]# curl 10.244.3.165/hostname.html
myapp-deploy-5695bb5658-95zxm
[root@k8s-master service]# 
[root@k8s-master service]# curl 10.244.3.164/hostname.html
myapp-deploy-5695bb5658-xtxbp

Service的ClusterIP类型信息

yaml文件

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
[root@k8s-master service]# pwd
/root/k8s_practice/service
[root@k8s-master service]# cat myapp-svc-ClusterIP.yaml 
apiVersion: v1
kind: Service
metadata:
  name: myapp-clusterip
  namespace: default
spec:
  type: ClusterIP  # 可以不写，为默认类型
  selector:
    app: myapp
    release: v1
  ports:
  - name: http
    port: 8080  # 对外暴露端口
    targetPort: 80  # 转发到后端端口

启动Service并查看状态

1
2
3
4
5
6
7
[root@k8s-master service]# kubectl apply -f myapp-svc-ClusterIP.yaml 
service/myapp-clusterip created
[root@k8s-master service]# 
[root@k8s-master service]# kubectl get svc -o wide
NAME              TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)    AGE   SELECTOR
kubernetes        ClusterIP   10.96.0.1        <none>        443/TCP    16d   <none>
myapp-clusterip   ClusterIP   10.102.246.104   <none>        8080/TCP   6s    app=myapp,release=v1

查看ipvs信息

1
2
3
4
5
6
7
8
9
[root@k8s-master service]# ipvsadm -Ln
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
………………
TCP  10.102.246.104:8080 rr
  -> 10.244.2.111:80              Masq    1      0          0  
  -> 10.244.3.164:80              Masq    1      0          0  
  -> 10.244.3.165:80              Masq    1      0          0

由此可见，正常情况下：当我们访问Service时，访问链路是能够传递到后端的Pod并返回信息。

Curl访问结果

直接访问Pod，如下所示是能够正常访问的。

1
2
3
4
5
6
7
8
[root@k8s-master service]# curl 10.244.2.111/hostname.html
myapp-deploy-5695bb5658-7tgfx
[root@k8s-master service]# 
[root@k8s-master service]# curl 10.244.3.165/hostname.html
myapp-deploy-5695bb5658-95zxm
[root@k8s-master service]# 
[root@k8s-master service]# curl 10.244.3.164/hostname.html
myapp-deploy-5695bb5658-xtxbp

但通过Service访问结果异常，信息如下。

1
2
[root@k8s-master service]# curl 10.102.246.104:8080
curl: (7) Failed connect to 10.102.246.104:8080; Connection timed out

处理过程

抓包核实

使用如下命令进行抓包，并通过Wireshark工具进行分析。

1
tcpdump -i any -n -nn port 80 -w ./$(date +%Y%m%d%H%M%S).pcap

结果如下图：

image

可见，已经向Pod发了请求，但是没有得到回复。结果TCP又重传了【TCP Retransmission】。

查看kube-proxy日志

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
[root@k8s-master service]# kubectl get pod -A | grep 'kube-proxy'
kube-system            kube-proxy-6bfh7                             1/1     Running   1          3h52m
kube-system            kube-proxy-6vfkf                             1/1     Running   1          3h52m
kube-system            kube-proxy-bvl9n                             1/1     Running   1          3h52m
[root@k8s-master service]# 
[root@k8s-master service]# kubectl logs -n kube-system kube-proxy-6bfh7
W0601 13:01:13.170506       1 feature_gate.go:235] Setting GA feature gate SupportIPVSProxyMode=true. It will be removed in a future release.
I0601 13:01:13.338922       1 node.go:135] Successfully retrieved node IP: 172.16.1.112
I0601 13:01:13.338960       1 server_others.go:172] Using ipvs Proxier.  ##### 可见使用的是ipvs模式
W0601 13:01:13.339400       1 proxier.go:420] IPVS scheduler not specified, use rr by default
I0601 13:01:13.339638       1 server.go:571] Version: v1.17.4
I0601 13:01:13.340126       1 conntrack.go:100] Set sysctl 'net/netfilter/nf_conntrack_max' to 131072
I0601 13:01:13.340159       1 conntrack.go:52] Setting nf_conntrack_max to 131072
I0601 13:01:13.340500       1 conntrack.go:83] Setting conntrack hashsize to 32768
I0601 13:01:13.346991       1 conntrack.go:100] Set sysctl 'net/netfilter/nf_conntrack_tcp_timeout_established' to 86400
I0601 13:01:13.347035       1 conntrack.go:100] Set sysctl 'net/netfilter/nf_conntrack_tcp_timeout_close_wait' to 3600
I0601 13:01:13.347703       1 config.go:313] Starting service config controller
I0601 13:01:13.347718       1 shared_informer.go:197] Waiting for caches to sync for service config
I0601 13:01:13.347736       1 config.go:131] Starting endpoints config controller
I0601 13:01:13.347743       1 shared_informer.go:197] Waiting for caches to sync for endpoints config
I0601 13:01:13.448223       1 shared_informer.go:204] Caches are synced for endpoints config 
I0601 13:01:13.448236       1 shared_informer.go:204] Caches are synced for service config

可见kube-proxy日志无异常

网卡设置并修改

备注：在k8s-master节点操作的

之后进一步搜索表明，这可能是由于“Checksum offloading” 造成的。信息如下：

1
2
3
4
5
6
7
8
[root@k8s-master service]# ethtool -k flannel.1 | grep checksum
rx-checksumming: on
tx-checksumming: on     ##### 当前为 on
	tx-checksum-ipv4: off [fixed]
	tx-checksum-ip-generic: on    ##### 当前为 on
	tx-checksum-ipv6: off [fixed]
	tx-checksum-fcoe-crc: off [fixed]
	tx-checksum-sctp: off [fixed]

flannel的网络设置将发送端的checksum打开了，而实际应该关闭，从而让物理网卡校验。操作如下：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
# 临时关闭操作
[root@k8s-master service]# ethtool -K flannel.1 tx-checksum-ip-generic off  
Actual changes:
tx-checksumming: off
	tx-checksum-ip-generic: off
tcp-segmentation-offload: off
	tx-tcp-segmentation: off [requested on]
	tx-tcp-ecn-segmentation: off [requested on]
	tx-tcp6-segmentation: off [requested on]
	tx-tcp-mangleid-segmentation: off [requested on]
udp-fragmentation-offload: off [requested on]
[root@k8s-master service]# 
# 再次查询结果
[root@k8s-master service]# ethtool -k flannel.1 | grep checksum
rx-checksumming: on
tx-checksumming: off     ##### 当前为 off
	tx-checksum-ipv4: off [fixed]
	tx-checksum-ip-generic: off     ##### 当前为 off
	tx-checksum-ipv6: off [fixed]
	tx-checksum-fcoe-crc: off [fixed]
	tx-checksum-sctp: off [fixed]

当然上述操作只能临时生效。机器重启后flannel虚拟网卡还会开启Checksum校验。

之后我们再次curl尝试

1
2
3
4
5
6
7
8
9
10
11
12
13
14
[root@k8s-master ~]# curl 10.102.246.104:8080
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[root@k8s-master ~]# 
[root@k8s-master ~]# curl 10.102.246.104:8080/hostname.html
myapp-deploy-5695bb5658-7tgfx
[root@k8s-master ~]# 
[root@k8s-master ~]# curl 10.102.246.104:8080/hostname.html
myapp-deploy-5695bb5658-95zxm
[root@k8s-master ~]# 
[root@k8s-master ~]# curl 10.102.246.104:8080/hostname.html
myapp-deploy-5695bb5658-xtxbp
[root@k8s-master ~]# 
[root@k8s-master ~]# curl 10.102.246.104:8080/hostname.html
myapp-deploy-5695bb5658-7tgfx

由上可见，能够正常访问了。

永久关闭flannel网卡发送校验

备注：所有机器都操作

使用以下代码创建服务

1
2
3
4
5
6
7
8
9
10
11
[root@k8s-node02 ~]# cat /etc/systemd/system/k8s-flannel-tx-checksum-off.service 
[Unit]
Description=Turn off checksum offload on flannel.1
After=sys-devices-virtual-net-flannel.1.device

[Install]
WantedBy=sys-devices-virtual-net-flannel.1.device

[Service]
Type=oneshot
ExecStart=/sbin/ethtool -K flannel.1 tx-checksum-ip-generic off

开机自启动，并启动服务

1
2
systemctl enable k8s-flannel-tx-checksum-off
systemctl start  k8s-flannel-tx-checksum-off

相关阅读

1、关于k8s的ipvs转发svc服务访问慢的问题分析(一)

2、Kubernetes + Flannel: UDP packets dropped for wrong checksum – Workaround

<-------------the end------------->
lightzhang wechat
欢迎扫一扫，订阅我的微信公众号！
坚持原创分享，你的支持就是我最大的动力！