Function to read and format K8s ConfigMap data from file

configmap_from_file.sh

# Function to read and format ConfigMap data from file
configmap_from_file() {
    local FILE=${1:?FILE is required}
    local INDENT=${2:-4}
    local SPACES=$(printf ' %.0s' {1..$INDENT})
    echo "|" && cat $FILE | sed "s/^/$SPACES/"
}

##################################################
# usage

# create nginx.conf.template
echo "server {
  listen 80 default_server;
  listen [::]:80 default_server;

  server_name _;
  
  location = /health {
    access_log off;
    add_header 'Content-Type' 'text/plain';
    return 200 'OK';
  }
}" > nginx.conf.template

# export configmap_from_file
export NGINX_CONF=$(configmap_from_file nginx.conf.template)

# kubectl apply
echo "apiVersion: v1
kind: ConfigMap
metadata:
  name: nginx-conf
data:
  nginx.conf.template: ${NGINX_CONF}"
| envsubst | kubectl apply -f -