Kubernetes Skew calculator

skew.bash

### This script attempts to calculate the skew of the population of pods across the nodes in a Kubernetes cluster.
### It takes taints into account, but does not consider pod labels.

NAMESPACE="app"
_all_nodes=$(kubectl get nodes | wc -l)
_all_nodes=$(( _all_nodes - 1 ))

for deployment_name in $(kubectl get -n ${NAMESPACE} deployment --template='{{range.items}}{{.metadata.name}}{{"\n"}}{{end}}'); do
  _deployment=$(kubectl get -n app -o json deployment ${deployment_name} | jq -c '.')
  _nodeTaintsPolicy=$(echo "${_deployment}" | jq -r '.spec.template.spec.topologySpreadConstraints[0].nodeAffinityPolicy')

  if [ "${_nodeTaintsPolicy}" == "Honor" ]; then
    _compatible_nodes=""
    for deployment_toleration in $(echo "${_deployment}" | jq -c '.spec.template.spec.tolerations[]')
    do
      _filter=""
      _key=$(echo "${deployment_toleration}" | jq -r 'if(.key == null) then empty else .key end')
      [ "${_key}" != "" ] && _filter=".key == \"${_key}\" and"

      _operator=$(echo "${deployment_toleration}" | jq -r 'if(.operator == null) then empty else .operator end')
      if [ "${_operator}" == "Exists" ]; then
        _value=""
      else
        _value=$(echo "${deployment_toleration}" | jq -r 'if(.value == null) then empty else .value end')
      fi
      [ "${_value}" != "" ] && _filter="${_filter} .value == \"${_value}\" and"

      _effect=$(echo "${deployment_toleration}" | jq -r 'if(.effect == null) then empty else .effect end')
      [ "${_effect}" != "" ] && _filter="${_filter} .effect == \"${_effect}\" and"

      _filter=$(echo "${_filter}" | sed 's/ and$//')

      _new_nodes=$(kubectl get nodes -o json | jq -r '.items[] | select(.spec.taints != null) | select(.spec.taints[] | '"${_filter}"') | .metadata.name')
      _compatible_nodes=$(echo ${_compatible_nodes}" "${_new_nodes})
    done
    _number_of_compatible_nodes=$(echo "${_compatible_nodes}" | sort -u | tr ' ' '\n' | wc -l)

  else
    _number_of_compatible_nodes=$(kubectl get nodes | wc -l)
  fi

  _population=$(kubectl get pods -n app -l app.kubernetes.io/name=${deployment_name} --template='{{range .items}}{{.spec.nodeName}}{{"\n"}}{{end}}' | sort | uniq -c | awk '{print $1}' | sort -n)
  _population_size=$(echo "${_population}" | wc -l)
  _max_population=$(echo "${_population}" | tail -n 1)
  _replicas=$(echo "${_deployment}" | jq -r '.spec.replicas')
  if [[ "${_replicas}" > "${_all_nodes}" ]] && [[ "${_population_size}" != "${_all_nodes}" ]]; then
    _min_population="0"
  else
    _min_population=$(echo "${_population}" | head -n 1)
  fi
  _skew="$((_max_population-_min_population))"
  echo "${deployment_name} skew: $_skew"
done