Kubernetes plugin 範例
上篇文章中我們介紹了 kubectl plugin 的系統與生態系，後來我們使用 krew 這個工具來管理各式各樣的 kubectl plugin
因此本篇就從裡面挑選一些 plugin 試試看。
View Allocations
我們這邊可以隨便挑一些 plugin 來玩看看
$ kubectl krew install view-allocations
Updated the local copy of plugin index.
Installing plugin: view-allocations
Installed plugin: view-allocations
\
| Use this plugin:
| kubectl view-allocations
| Documentation:
| https://github.com/davidB/kubectl-view-allocations
/
WARNING: You installed plugin "view-allocations" from the krew-index plugin repository.
These plugins are not audited for security by the Krew maintainers.
Run them at your own risk.
這邊要注意，因為我們安裝的都是 kubectl plugin 所以最後執行的時候不需要補上 krew ，譬如我們上面安裝 view-allocations，安裝完畢後直接執行 kubectl view-allocations來看
View-allocations 是一個用來顯示系統上所有 有設定 resource 限定的資源 數量都列出來，可以幫助你評估當前每個節點上總共有多少 CPU/Memory，然後上面運行的資源目前總共要求多少，百分比多少。
要注意的是，如果你的 Pod 沒有用 resource limited 去限制，就不會出現在系統上
$ kubectl view-allocations
Resource Requested %Requested Limit %Limit Allocatable Free
cpu 1050.0m 9% 300.0m 2% 12.0 10.9
├─ kind-control-plane 850.0m 21% 100.0m 2% 4.0 3.1
│ ├─ coredns-6955765f44-l4z47 100.0m 0.0
│ ├─ coredns-6955765f44-zb5xx 100.0m 0.0
│ ├─ kindnet-czpsv 100.0m 100.0m
│ ├─ kube-apiserver-kind-control-plane 250.0m 0.0
│ ├─ kube-controller-manager-kind-control-plane 200.0m 0.0
│ └─ kube-scheduler-kind-control-plane 100.0m 0.0
├─ kind-worker 100.0m 2% 100.0m 2% 4.0 3.9
│ └─ kindnet-sbqxd 100.0m 100.0m
└─ kind-worker2 100.0m 2% 100.0m 2% 4.0 3.9
└─ kindnet-sw5mq 100.0m 100.0m
ephemeral-storage 0.0 0% 0.0 0% 581.5Gi 581.5Gi
├─ kind-control-plane 0.0 0% 0.0 0% 193.8Gi 193.8Gi
├─ kind-worker 0.0 0% 0.0 0% 193.8Gi 193.8Gi
└─ kind-worker2 0.0 0% 0.0 0% 193.8Gi 193.8Gi
memory 290.0Mi 1% 490.0Mi 1% 46.9Gi 46.4Gi
├─ kind-control-plane 190.0Mi 1% 390.0Mi 2% 15.6Gi 15.3Gi
│ ├─ coredns-6955765f44-l4z47 70.0Mi 170.0Mi
│ ├─ coredns-6955765f44-zb5xx 70.0Mi 170.0Mi
│ └─ kindnet-czpsv 50.0Mi 50.0Mi
├─ kind-worker 50.0Mi 0% 50.0Mi 0% 15.6Gi 15.6Gi
│ └─ kindnet-sbqxd 50.0Mi 50.0Mi
└─ kind-worker2 50.0Mi 0% 50.0Mi 0% 15.6Gi 15.6Gi
└─ kindnet-sw5mq 50.0Mi 50.0Mi
pods 0.0 0% 0.0 0% 330.0 330.0
├─ kind-control-plane 0.0 0% 0.0 0% 110.0 110.0
├─ kind-worker 0.0 0% 0.0 0% 110.0 110.0
└─ kind-worker2 0.0 0% 0.0 0% 110.0 110.0
這個工具我個人認為還滿好用的，畢竟可以幫你顯示出當前系統上運算資源所使用的 CPU/Memory 等使用量，這些使用量可以用來幫助開發者判斷要如何設定相關的資源限制。
change-ns
這套工具相對簡單，就是幫你切換預設的 namespace，減少每次輸入指令的時候都要一直透過 -n|--namespace 來指定特定的 namespace。
$ kubectl krew install change-ns
Updated the local copy of plugin index.
Installing plugin: change-ns
Installed plugin: change-ns
\
| Use this plugin:
| kubectl change-ns
| Documentation:
| https://github.com/juanvallejo/kubectl-ns
/
WARNING: You installed plugin "change-ns" from the krew-index plugin repository.
These plugins are not audited for security by the Krew maintainers.
Run them at your own risk.
$ kubectl change-ns kube-system
namespace changed to "kube-system"
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
coredns-6955765f44-l4z47 1/1 Running 0 2d13h
coredns-6955765f44-zb5xx 1/1 Running 0 2d13h
etcd-kind-control-plane 1/1 Running 0 2d13h
kindnet-czpsv 1/1 Running 0 2d13h
kindnet-sbqxd 1/1 Running 0 2d13h
kindnet-sw5mq 1/1 Running 0 2d13h
kube-apiserver-kind-control-plane 1/1 Running 0 2d13h
kube-controller-manager-kind-control-plane 1/1 Running 0 2d13h
kube-proxy-4b5rl 1/1 Running 0 2d13h
kube-proxy-nrspx 1/1 Running 0 2d13h
kube-proxy-skfm5 1/1 Running 0 2d13h
kube-scheduler-kind-control-plane 1/1 Running 0 2d13h
類似的工具還有ctx ，可以幫切換不同的 kubeconfig context，讓你更方便的於多個 Kubernetes Cluster 中切換
Status
這個工具算是幫你把 description 的資訊再次整理，舉例來說我們準備了一個 pull image 會失敗的案例，這時候我們用 status 這個指令來試試看
$ kubectl krew install status
Updated the local copy of plugin index.
Installing plugin: status
Installed plugin: status
\
| Use this plugin:
| kubectl status
| Documentation:
| https://github.com/bergerx/kubectl-status
/
WARNING: You installed plugin "status" from the krew-index plugin repository.
These plugins are not audited for security by the Krew maintainers.
Run them at your own risk.
安裝完畢後我們針對一個失敗的 pod 來使用 kubectl status pod xxxx
$ kubectl status pod pull-fail
Pod/pull-fail -n default, created 2m ago Pending Burstable
PodScheduled -> Initialized -> Not ContainersReady -> Not Ready
Ready ContainersNotReady, containers with unready status: [getting-started] for 2m
ContainersReady ContainersNotReady, containers with unready status: [getting-started] for 2m
Standalone POD.
Containers:
getting-started (hwchiu/netutils-qq) Waiting ErrImagePull: rpc error: code = Unknown desc = failed to pull and unpack image "docker.io/hwchiu/netutils-qq:latest": failed to resolve reference "docker.io/hwchiu/netutils-qq:latest": pull access denied, repository does not exist or may require authorization: server message: insufficient_scope: authorization failed
Events:
Scheduled 2m ago from default-scheduler: Successfully assigned default/pull-fail to kind-worker
Pulling 28s ago (x4 over 1m) from kubelet,kind-worker: Pulling image "hwchiu/netutils-qq"
Failed 28s ago (x4 over 1m) from kubelet,kind-worker: Failed to pull image "hwchiu/netutils-qq": rpc error: code = Unknown desc = failed to pull and unpack image "docker.io/hwchiu/netutils-qq:latest": failed to resolve reference "docker.io/hwchiu/netutils-qq:latest": pull access denied, repository does not exist or may require authorization: server message: insufficient_scope: authorization failed
Failed 28s ago (x4 over 1m) from kubelet,kind-worker: Error: ErrImagePull
BackOff 13s ago (x6 over 1m) from kubelet,kind-worker: Back-off pulling image "hwchiu/netutils-qq"
Failed 13s ago (x6 over 1m) from kubelet,kind-worker: Error: ImagePullBackOff
上面可以看到一些資訊，譬如說
- PodScheduled -> Initialized -> Not ContainersReady -> Not Ready
Pod 失敗是因為卡在
ContainersReady這個狀態會失敗，導致最後整個 Pod 沒有成功 - Standalone POD 這個 Pod 本身沒有任何的 StatefulSet/ReplicaSet，而是獨立的 Pod
- Containers: 底下就是一些詳細訊息，譬如為什麼會失敗
- Events: 這個 Pod 的一些事件資訊
除了 Pod 之外， Status 也可以用來看其他的資源，有興趣可以玩看看
access-matrix
接下來這個工具主要是用來列出當前使用者對於系統上的全部 Resource的權限資訊，主要是該使用者對於特定資源上的不同動詞 (Get/Update/List/Delete) 等是否可以執行
$ kubectl krew install access-matrix
Updated the local copy of plugin index.
Installing plugin: access-matrix
Installed plugin: access-matrix
\
| Use this plugin:
| kubectl access-matrix
| Documentation:
| https://github.com/corneliusweig/rakkess
| Caveats:
| \
| | Usage:
| | kubectl access-matrix
| | kubectl access-matrix for pods
| /
/
WARNING: You installed plugin "access-matrix" from the krew-index plugin repository.
These plugins are not audited for security by the Krew maintainers.
Run them at your own risk.
此外也可以透過 --sa 等指令來切換不同的 service account，所以可以看到下列的範例，用不同的使用者去看權限，我預設的使用者有幾乎無敵的權限，什麼都可以執行。如果是系統上 kube-system:namespace-controller 則只能 LIST/DELETE。
除了這四個動詞之外，其實還有很多動詞可以用，只是預設情況下只會列出這四個
$ kubectl access-matrix --sa kube-system:namespace-controller
NAME LIST CREATE UPDATE DELETE
apiservices.apiregistration.k8s.io ✔ ✖ ✖ ✔
bindings ✖
certificatesigningrequests.certificates.k8s.io ✔ ✖ ✖ ✔
clusterrolebindings.rbac.authorization.k8s.io ✔ ✖ ✖ ✔
clusterroles.rbac.authorization.k8s.io ✔ ✖ ✖ ✔
componentstatuses ✔
configmaps ✔ ✖ ✖ ✔
controllerrevisions.apps ✔ ✖ ✖ ✔
cronjobs.batch ✔ ✖ ✖ ✔
csidrivers.storage.k8s.io ✔ ✖ ✖ ✔
.....
$ kubectl access-matrix
NAME LIST CREATE UPDATE DELETE
apiservices.apiregistration.k8s.io ✔ ✔ ✔ ✔
bindings ✔
certificatesigningrequests.certificates.k8s.io ✔ ✔ ✔ ✔
clusterrolebindings.rbac.authorization.k8s.io ✔ ✔ ✔ ✔
clusterroles.rbac.authorization.k8s.io ✔ ✔ ✔ ✔
componentstatuses ✔
configmaps ✔ ✔ ✔ ✔
controllerrevisions.apps ✔ ✔ ✔ ✔
cronjobs.batch ✔ ✔ ✔ ✔
csidrivers.storage.k8s.io ✔ ✔ ✔ ✔
starboard
最後來看一個跟安全性有關的 plugin
Starboard integrates security tools into the Kubernetes environment, so that users can find and view the risks that relate to different resources in a Kubernetes-native way. Starboard provides custom security resources definitions and a Go module to work with a range of existing security tools, as well as a
kubectl-compatible command-line tool and an Octant plug-in that make security reports available through familiar Kubernetes tools.
接下來示範怎麼用(假設已經安裝完畢)
$ kubectl starboard init
$ kubectl create deployment nginx --image nginx:1.16
先透過 starboard 去初始化相關資源，接者我們部署一個 nginx:1.16 的容器到系統中
$ kubectl starboard find vulnerabilities deployment/nginx
$ kubectl starboard get vulnerabilities deployment/nginx
....
summary:
criticalCount: 0
highCount: 4
lowCount: 93
mediumCount: 34
noneCount: 0
unknownCount: 0
vulnerabilities:
- description: Missing input validation in the ar/tar implementations of APT before
version 2.1.2 could result in denial of service when processing specially
crafted deb files.
fixedVersion: 1.8.2.1
installedVersion: 1.8.2
layerID: ""
links:
- https://bugs.launchpad.net/bugs/1878177
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-3810
- https://github.com/Debian/apt/issues/111
- https://github.com/julian-klode/apt/commit/de4efadc3c92e26d37272fd310be148ec61dcf36
- https://lists.debian.org/debian-security-announce/2020/msg00089.html
- https://lists.fedoraproject.org/archives/list/[email protected]/message/U4PEH357MZM2SUGKETMEHMSGQS652QHH/
- https://salsa.debian.org/apt-team/apt/-/commit/dceb1e49e4b8e4dadaf056be34088b415939cda6
- https://salsa.debian.org/jak/apt/-/commit/dceb1e49e4b8e4dadaf056be34088b415939cda6
- https://tracker.debian.org/news/1144109/accepted-apt-212-source-into-unstable/
- https://usn.ubuntu.com/4359-1/
- https://usn.ubuntu.com/4359-2/
- https://usn.ubuntu.com/usn/usn-4359-1
- https://usn.ubuntu.com/usn/usn-4359-2
resource: apt
severity: MEDIUM
title: ""
vulnerabilityID: CVE-2020-3810
...
可以看到上面有很多訊息，列出當前 image 上有哪些潛在的 CVE，如果覺得這樣看起來實在不討喜，可以使用 starboard-octant-plugin 這個整合專案，把上述的報告用 UI 的方式視覺話呈現出來，譬如說下圖(下圖節錄自 starboard-octant-plugin 官方 Repo)
到這邊為止，我們介紹了一些有趣的 Kubectl plugin，當然這些 plugin 本身也都是一個獨立的執行檔案，所以其實就算不透過 kubectl 來執行也是沒問題的，所有個工具都可以獨立使用。透過 krew 只是我們可以更方便的搜尋到有哪些 plugin 可以用，實務上要怎麼執行都是個人喜歡，方便，操作順暢即可。
Krew 上面的工具非常多，使用上可以都可以嘗試看看，也因為這樣才有辦法找到真的對自己日常工作有幫助的好幫手