Zulhilmi Zainudin zulhfreelancer

How to run a temporary psql container in Kubernetes for testing/debugging?

$ k run psql-client --rm -i --tty --image jbergknoff/postgresql-client --command /bin/sh
/ # which psql
/usr/bin/psql

/ # psql --version
psql (PostgreSQL) 12.3

How to sort `htop` by CPU or Memory?

Sort by CPU

htop -s PERCENT_CPU

Sort by Memory / RAM

How to displays a brief summary of all IPv4 addresses assigned to the network interfaces Linux system?

Command:

ip -4 -br a

Sample output:

How to check which network interface will be used to route/send packets for specific IP address?

# Install `ip` tool
apt update -y
apt install iproute2 -y

# Check
ip r get 8.8.8.8 fibmatch

Get all Prometheus metrics and descriptions/help texts

Requirement:

promtool

As JSON

curl -sg 'http://prom-server:prom-port/api/v1/metadata' | jq -r '.data'

How to install promtool by Prometheus?

# Fetch latest version
TAG=$(curl -s https://api.github.com/repos/prometheus/prometheus/releases | jq -r '.[] | .tag_name' | head -n 1)
echo $TAG

# Remove the `v` prefix
VERSION=$(echo $TAG | sed 's/v//')
echo $VERSION

How to query Prometheus from local CLI / Terminal

Requirements

promtool - see installation steps here

Command

promtool query instant '' '' | jq

How to filter Kubernetes nodes by label using `kubectl` and `jq`

# Get all control-plane nodes
kubectl get nodes -o json | jq -r '.items[] | select(.metadata.labels."node-role.kubernetes.io/control-plane"=="true").metadata.name'

# Get all worker nodes
kubectl get nodes -o json | jq -r '.items[] | select(.metadata.labels."node-role.kubernetes.io/control-plane"!="true").metadata.name'

	# Replace the THE_SECRET_NAME
	k get pods -A -o json \| jq -r '.items[] \| select(.spec.imagePullSecrets!=null) \| select(.spec.imagePullSecrets[].name=="THE_SECRET_NAME") \| {namespace: .metadata.namespace, name: .metadata.name}'