#2 - Learn to love kubectl ★ Tip #1 in action Add alias k=’kubectl’ to your .bashrc / .zshrc / .whateverrc KIND: VERSION: k get pods -A ★ The official docs offer a single page view of all built in commands: kubernetes.io/docs/reference/generated/kube ctl/kubectl-commands ★ k explain pods.spec.containers kubectl explain is your friend! Find out what any property of any Kubernetes resource is for. ➡ Pod v1 RESOURCE: containers <[]Object> DESCRIPTION: List of containers belonging to the pod. Containers cannot currently be added or removed. There must be at least one container in a Pod. Cannot be updated. A single application container that you want to run within a pod. FIELDS: args <[]string> Arguments to the entrypoint. The docker image’s CMD is used if this is not provided. Variable references $(VAR_NAME) are expanded using the container’s environment. If a variable cannot be resolved, the reference in the input string will be unchanged. Double $$ are reduced to a single $, which allows for escaping the $(VAR_NAME) syntax: i.e. “$$(VAR_NAME)” will produce the string literal “$(VAR_NAME)”. Escaped references will never be expanded, regardless of whether the variable exists or not. Cannot be updated. command <[]string> Entrypoint array. Not executed within a shell. The docker image’s ENTRYPOINT is used if this is not provided. Variable references $(VAR_NAME) Save time by only typing k. Kubectl explain for digging into resources and their properties (useful when you can’t access the official docs or know exactly what you’re looking for)

#5 - kubectl plugins ★ Any command in your $PATH that is prefixed with kubectl- becomes a kubectl plugin $ cat kubectl-hello #!/bin/bash ★ Krew - package manager for kubectl plugins echo “Hello, Kube” github.com/kubernetes-sigs/krew ★ Install plugins with: kubectl krew install <PLUGIN NAME> $ kubectl hello Hello, Kube ★ Some of my fave plugins: ○ stern - Multi-pod/container log tailing ○ tree - Show hierarchy of resources based on ownerReferences ○ outdated - Find containers with outdated images ○ gs - Giant Swarm’s plugin for working with our managed clusters Plugins can be in any language. You can easily add your own by creating Bash scripts with a kubectl- prefixed name. Note: autocomplete is a bit trickier here. Some plugins support it but generally expect your tabcompletion to only recommend core kubectl features.

#6 - Pod Debugging: kubectl debug Debugging a running pod - kubectl exec

kubectl exec my-broken-pod -it — sh

�� error: Internal error occurred: error executing command in container: failed to exec in container: failed to start exec…… Debugging a running pod - kubectl debug Requires Kubernetes v1.23

kubectl debug -it —image bash my-broken-pod Defaulting debug container name to debugger-gprmk. If you don’t see a command prompt, try pressing enter. bash-5.1#

kubectl exec is great for debugging misconfigured pods that aren’t crashing and have enough OS to exec into. But… If the pod is CrashLooping you’ll get kicked out of the session when it crashes. If the pod doesn’t have a shell you can exec into (e.g. a container that only has a Golang binary) you’ll not be able to exec kubectl debug is great for pods that either don’t have any OS ��

#6 - Pod Debugging: kubectl debug Example - investigate a CrashLooping pod

kubectl run debug-demo —image=bash — exit 1 # kubectl get pods debug-demo NAME debug-demo

READY 0/1 STATUS CrashLoopBackOff RESTARTS 2 (20s ago) AGE 44s This will prevent us from kubectl exec into the pod

kubectl debug -it —image bash debug-demo Defaulting debug container name to debugger-5mkjj. If you don’t see a command prompt, try pressing enter. bash-5.1#

kubectl debug has a few different modes: - launches an “ephemeral container” within the pod you’re debugging - kubectl debug - creates a copy of the pod with some values replaced (e.g. the image used) - kubectl debug –copy-to - launch a pod in the nodes host namespace to debug the node - kubectl debug node/my-node This has some limitations - cannot access all filesystem of failing container, only volumes that are shared

#7 - Node Debugging: kubectl debug (again) ★ Requires Kubernetes v1.23 # kubectl debug node/ip-10-0-0-1 -it —image alpine Creating debugging pod node-debugger-ip-10-0-0-1-9wlqp with container debugger on node ip-10-0-0-1. If you don’t see a command prompt, try pressing enter. / # ls -l / total 60 … drwxr-xr-x 2 root root 4096 Aug 9 08:47 home drwxr-xr-x 19 root root 4096 Nov 4 08:48 host The host node’s root filesystem drwxr-xr-x 7 root root 4096 Aug 9 08:47 lib drwxr-xr-x 5 root root 4096 Aug 9 08:47 media … / # Why not SSH? - I prefer to use ephemeral instances with the minimal needed to run Kubernetes, no sshd, no port 22 open etc. but there are times when you just need to check what’s actually going on with the underlying host machine. kubectl debug launches a pod on the node which allows for direct access to the node host. Processes and filesystem is available to you. Being your own toolkit with you depending on what --image you specify.

#7 - Node Debugging: nsenter alternative ★ For older clusters before Kubernetes v1.23 # kubectl run h0nk —rm -it \ —image alpine —privileged \ —overrides ‘{“spec”:{“hostPID”: true}}’\ —command nsenter – \ —mount=/proc/1/ns/mnt If you don’t see a command prompt, try pressing enter. # ★ Alternatives: github.com/AverageMarcus/kube-ssh github.com/giantswarm/kubectl-enter This won’t work with Talos, for example, whereas kubectl debug will ★ Note: Underlying host needs a shell Only needed if kubectl debug not available for your cluster. A one-liner to exec into a privileged pod and switch to the host namespace using nsenter - small enough to fit in a Tweet or on a sticker! More “packaged” alternatives available with kube-ssh or kubectl-enter

#8 - Webhooks OK, actually 3 but we’re ignoring CRD conversion webhooks ★ Two types of webhooks: ValidatingWebhook Ability to block actions against the API server if fails to meet given criteria. MutatingWebhook Modify requests before passing them on to the API server. ★ Implement more advanced access control than is possible with RBAC. [Restricting cluster-admin permissions] ★ Add default labels to resources as they’re created. ★ Enforce policies such as not using latest as an image tag or ensuring all workloads have resource requests/limits specified. ★ “Hotfix” for security issues (e.g. mutating all pods to include a LOG4J_FORMAT_MSG_NO_LOOKUPS env var to prevent Log4Shell exploit). [Log4Shell Mitigation] Allows for subtractive access control (take away a users ability to perform a certain action against a certain resource) - something not possible with RBAC See blog post about how we avoided a nasty bug in our CLI tool with a ValidatingWebhook. https://www.giantswarm.io/blog/restricting-cluster-admin-permissions

#8 - Webhooks ★ Build your own operator to implement custom logic ★ Kyverno - Kubernetes native policy management. Create Policy and ClusterPolicy resources to define rules in YAML ★ OPA Gatekeeper - Policy management built on top of Open Policy Agent Kyverno Policy apiVersion: kyverno.io/v1 kind: ClusterPolicy metadata: name: block-bulk-certconfigs-delete annotations: policies.kyverno.io/description: Block delete all bug in CLI spec: rules: - name: block-bulk-certconfigs-delete match: any: - resources: kinds: [CertConfig] preconditions: any: - key: “” operator: Equals value: “” validate: message: | Your current kubectl-gs version contains a critical bug deny: conditions: - key: “” operator: In value: [DELETE] Taken from our Restricting cluster-admin permissions blog post Three most common approaches to leverage webhooks

#8 - Webhooks Notes: This is one of the main causes we see of clusters being down ★ Where possible always avoid applying webhooks to resources in kube-system. This can cause a deadlock if those pods try to come up before the webhook service is available. ★ Be aware of the failurePolicy property - it defaults to “fail” which can cause troubles if your service handling the webhook goes down. ★ The reinvocationPolicy property can be set if changes made by a MutatingWebhook may need to go through other defined webhooks again. ★ Ordering - first MutatingWebhooks then ValidatingWebhooks. No guaranteed control of order within these two phases. Webhooks can break a cluster. Make sure your service is resilient and that your webhooks don’t block critical workloads. Webhooks can be backed by either services within the cluster or pointing to an URL outside of the cluster.