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Useful guides, documents, snippets for working with tech.

Introduction
The Craft of Programming
Kubernetes
Vim
- Quick Replace
Programming Languages
- TypeScript

Introduction

This is a set of assorted documents, snippets and links I've found useful and often refer to.

The Craft of Programming

These documents relate to the craft of engineering - not how to solve specific problems, but how to think about designing solutions.

(AHA Programming 💡)[https://kentcdodds.com/blog/aha-programming/] - The dangers of DRY, the web of WET, the awesomeness of AHA.

Kubernetes

Set the Current Context

kubectl config use-context something

Setting Cluster Credentials on the Command Line

If you don't want to create certificate files and so on and instead use fields like certificate-authority-data, it can be tricky to work out how to set these values from the CLI.

Here's how you do it:

K8S_CLUSTER_NAME="mycluster"
K8S_CONTEXT_NAME="mycluster"
K8S_CONTEXT_NAMESPACE="develop"
K8S_SERVER="https://whatever.com:8443"
K8S_USERNAME="pegasus-user"
K8S_CLUSTER_CERTIFICATE_AUTHORITY_DATA="<snip>"
K8S_CLUSTER_CLIENT_KEY_DATA="<snip>"
K8S_CLUSTER_TOKEN="<snip>"

# Create the cluster configuration which we can set using 'standard' commands.
kubectl config set-cluster ${K8S_CLUSTER_NAME} -server="${K8S_SERVER}"
kubectl config set-context ${K8S_CONTEXT_NAME} --user="${K8S_USERNAME}" --cluster="${CLUSTER_NAME}" --namespace="${K8S_CONTEXT_NAMESPACE}"

# Now set the credentials.
kubectl config set clusters.${CLUSTER_NAME}.certificate-authority-data "${K8S_CLUSTER_CERTIFICATE_AUTHORITY_DATA}"
kubectl config set users.${K8S_USERNAME}.client-key-data "${K8S_CLUSTER_CLIENT_KEY_DATA}"
kubectl config set users.${K8S_USERNAME}.token "${K8S_CLUSTER_TOKEN}"

Deleting namespaces stuck in 'terminating'

Check out this excellent solution from:

https://github.com/kubernetes/kubernetes/issues/60807

(Modified a bit)

kubectl proxy &
kubectl_proxy_pid=$!

for namespace in $(kubectl get namespaces | grep Terminating | awk '{print $1}'); do
  echo "processing $namespace"
  kubectl get namespace $namespace -o json | jq 'del(.spec.finalizers)' | curl -k -H "Content-Type: application/yaml" -X PUT -d @- http://127.0.0.1:8001/api/v1/namespaces/$namespace/finalize
done

kill $kubectl_proxy_pid

Setting the default namespace for commands

Easy:

k config set-context --current --namespace ingress-nginx

Dealing with broken etcd

There's an excellent set of tips here:

https://github.com/kubernetes-sigs/kubespray/issues/3471#issuecomment-530036084

This was the only solution I could find when I had blatted some etcd configuration by re-creating a master node (with a new IP, but the same name). This required a new set of certificates etc to be generated. There were some persistent problems using Kubespray; following the tips here solved them.

Vim

Quick Replace

Go to the word you want to replace, then in command mode just use Ctrl+R Ctrl+W to paste the word into the command editor, e.g.

:%s/<now type Ctrl+R Ctrl+W>

This works because CTRL-R is used to insert a register in either command or insert mode. In command mode CTRL-W is the word under the cursor. Other related tricks

CTRL-R + \ - Insert the last search term
CTRL-R + a - Insert a register named a
CTRL-R + = - Insert the result of an expression (e.g. 3*78)

More info: :help i_CTRL-R and :help c_CTRL-R.

Programming Languages

TypeScript

Beginner friendly and to-the-point overview of TypeScript, assuming the reader already knows JavaScript:

https://github.com/rmolinamir/typescript-cheatsheet