openshift/k8s, 远程shell / oc exec, 原理
我们在日常运维openshift/k8s的时候，经常会运行oc exec命令，比如
oc exec -it $pod_name -- bash
但是，有的时候，这个session会连不上，有的时候，这个session会突然中断，接下来我们就尝试看看这个命令背后的原理
oc exec -v 6 -it pod/du-deployment1-58944f9f85-8m49m -- bash
# I1230 14:38:39.347429 188014 loader.go:372] Config loaded from file: /data/install/auth/kubeconfig
# I1230 14:38:39.370718 188014 round_trippers.go:454] GET https://api.ocp4s.redhat.ren:6443/api/v1/namespaces/default/pods/du-deployment1-58944f9f85-8m49m 200 OK in 10 milliseconds
# I1230 14:38:39.376109 188014 podcmd.go:88] Defaulting container name to du-container1
# I1230 14:38:39.396350 188014 round_trippers.go:454] POST https://api.ocp4s.redhat.ren:6443/api/v1/namespaces/default/pods/du-deployment1-58944f9f85-8m49m/exec?command=bash&container=du-container1&stdin=true&stdout=true&tty=true 101 Switching Protocols in 19 milliseconds
# [root@du-deployment1-58944f9f85-8m49m /]#
oc exec -v 7 -it pod/du-deployment1-58944f9f85-8m49m -- bash
# I1230 14:39:13.441167 188023 loader.go:372] Config loaded from file: /data/install/auth/kubeconfig
# I1230 14:39:13.450807 188023 round_trippers.go:432] GET https://api.ocp4s.redhat.ren:6443/api/v1/namespaces/default/pods/du-deployment1-58944f9f85-8m49m
# I1230 14:39:13.450830 188023 round_trippers.go:438] Request Headers:
# I1230 14:39:13.450837 188023 round_trippers.go:442] Accept: application/json, */*
# I1230 14:39:13.450842 188023 round_trippers.go:442] User-Agent: oc/4.9.0 (linux/amd64) kubernetes/96e95ce
# I1230 14:39:13.465425 188023 round_trippers.go:457] Response Status: 200 OK in 14 milliseconds
# I1230 14:39:13.473072 188023 podcmd.go:88] Defaulting container name to du-container1
# I1230 14:39:13.475155 188023 round_trippers.go:432] POST https://api.ocp4s.redhat.ren:6443/api/v1/namespaces/default/pods/du-deployment1-58944f9f85-8m49m/exec?command=bash&container=du-container1&stdin=true&stdout=true&tty=true
# I1230 14:39:13.475182 188023 round_trippers.go:438] Request Headers:
# I1230 14:39:13.475187 188023 round_trippers.go:442] X-Stream-Protocol-Version: v4.channel.k8s.io
# I1230 14:39:13.475191 188023 round_trippers.go:442] X-Stream-Protocol-Version: v3.channel.k8s.io
# I1230 14:39:13.475195 188023 round_trippers.go:442] X-Stream-Protocol-Version: v2.channel.k8s.io
# I1230 14:39:13.475199 188023 round_trippers.go:442] X-Stream-Protocol-Version: channel.k8s.io
# I1230 14:39:13.475203 188023 round_trippers.go:442] User-Agent: oc/4.9.0 (linux/amd64) kubernetes/96e95ce
# I1230 14:39:13.496289 188023 round_trippers.go:457] Response Status: 101 Switching Protocols in 21 milliseconds
# [root@du-deployment1-58944f9f85-8m49m /]#
上面2个命令，我们打开了log，等级设置不同，可以看到oc exec命令，其实是调用了api server上的pod接口，然后通道协议切换到了x-stream
那么我们在项目上，发现oc exec不稳定，那就要先去看api server是不是正常，在通往api server的通路上，是不是有haproxy之类的代理，代理是否正常。这样逐步的排查。
reference
- https://www.cnblogs.com/a00ium/p/10905279.html
- https://cloud.redhat.com/blog/executing-commands-in-pods-using-k8s-api
- https://docs.openshift.com/container-platform/4.9/rest_api/workloads_apis/pod-core-v1.html#apiv1namespacesnamespacepodsnameexec