A little script to scale down a stateful set one by one

scale-down-controlled.sh

#!/usr/bin/env bash

# This script scales down a stateful set in a controlled way one by one.


set -euo pipefail
set -x

KUBERNETES_CONTEXT=${KUBERNETES_CONTEXT:-dev-us-central-0}
KUBERNETES_NAMESPACE=${KUBERNETES_NAMESPACE:-fire-dev-001}
k="kubectl --namespace ${KUBERNETES_NAMESPACE} --context ${KUBERNETES_CONTEXT} "

NAME=pyroscope-ingester
TARGET_REPLICAS=3

while true; do
    CURRENT_REPLICAS=$($k get "sts/${NAME}" -o jsonpath='{.spec.replicas}')
    if [ "${CURRENT_REPLICAS}" -lt "$((TARGET_REPLICAS + 1))" ]; then
        echo "done"
        exit 0
    fi
    next=$((CURRENT_REPLICAS - 1))
    $k scale "--current-replicas=$CURRENT_REPLICAS" "--replicas=${next}" "sts/${NAME}"

    # wait extra for luck
    $k wait --timeout 600s --for=delete "pod/${NAME}-${next}"
    sleep 2
done