Help script to demote kafka leader node

demote-leader.sh

#!/bin/bash -e

# Demoting leader is a necessary step before moving replicas off that node otherwise follower fetchers may crash due to a kafka bug.
# This script makes use of replica-reassign.sh script to demote a node from preferred leader in the given topic-partition's replicas list
# It then forces a preferred leader election for this topic-partition.

usage() {
  echo "Usage: $0 -t <topic-name> -p <partition-number> -n <node-id> [-z <zookeeper-host>]"
  echo "For example, if topic 'foo' partition 0 has replicas list [0,1,2]"
  echo "Running command '$0 -t foo -p 0 -n 0' will change the order to [1,2,0]"
  echo "Then kafka-preferred-replica-election.sh should force kafka to re-elect the preferred node as leader"
  exit "$1"
}

while [[ $# -gt 0 ]]; do
opt="$1"
case $opt in
    -t|--topic)
      TOPIC="$2"
      shift 2
      ;;
    -p|--partition)
      PARTITION="$2"
      shift 2
      ;;
    -n|--node)
      NODE_TO_DEMOTE="$2"
      shift 2
      ;;
    -z|--zookeeper)
      ZOOKEEPER="$2"
      shift 2
      ;;
    -h|--help)
      usage 0
      ;;
    *)
      echo "Unknown option $opt"
      exit 1
      ;;
esac
done

[ -z "$TOPIC" ] && echo "-t|--topic is missing" && usage 1
[ -z "$PARTITION" ] && echo "-p|--partition is missing" && usage 1
[ -z "$NODE_TO_DEMOTE" ] && echo "-n|--node is missing" && usage 1
[ -z "$ZOOKEEPER" ] && echo "ZOOKEEPER is not defined and -z|--zookeeper is missing" && usage 1

THIS_DIR="$(cd "$(dirname "$0")" && pwd)"
REASSIGN="$THIS_DIR/replica-reassign.sh"
DESCRIBE="$THIS_DIR/kafka-topics.sh"
ELECT_PREFERRED_LEADER="$THIS_DIR/kafka-preferred-replica-election.sh"
if [ ! -f "$REASSIGN" ]; then echo "Can not find $REASSIGN"; exit 1; fi
if [ ! -f "$DESCRIBE" ]; then echo "Can not find $DESCRIBE"; exit 1; fi
if [ ! -f "$ELECT_PREFERRED_LEADER" ]; then echo "Can not find $ELECT_PREFERRED_LEADER"; exit 1; fi

describe_line=""
replicas_csv=""
current_leader_node=""
describe() {
  describe_line="$($DESCRIBE --zookeeper "$ZOOKEEPER" --topic "$TOPIC" --describe | grep -E "Partition:\s$PARTITION\s")"
  replicas_csv="$(echo "$describe_line" | sed -e 's#^.*Replicas:\(.*\)Isr.*#\1#' | tr -d ' \t')"
  current_leader_node="$(echo "$describe_line" | sed -e 's#^.*Leader:\(.*\)Replicas.*#\1#' | tr -d ' \t')"
}

describe

IFS=',' read -r -a replicas_array <<< "$replicas_csv"
replicas_count="${#replicas_array[@]}"
if [ ! "$replicas_count" -gt 1 ]; then
  echo "Not enough replicas"
  echo "$describe_line"
  exit 1
fi

found="no"
for node in "${replicas_array[@]}"; do
  if [ "$node" -eq "$NODE_TO_DEMOTE" ]; then
    found="yes"
    break
  fi
done

if [ "no" = "$found" ]; then
  echo "Node $NODE_TO_DEMOTE is not in replicas list for $TOPIC-$PARTITION: $replicas_csv. Skipped demoting!"
  exit 0
fi

# first element in the array is the preferred leader
current_preferred_leader="${replicas_array[0]}"
if [ "$current_preferred_leader" != "$NODE_TO_DEMOTE" ]; then
  echo "Node $NODE_TO_DEMOTE is not preferred leader for $TOPIC-$PARTITION: $replicas_csv. Skipped replica reordering!"
else
  # reorder replicas list
  # only reordering, no need for --throttle and --reoder-replicas
  reordered_replicas_csv=""
  for i in $(seq 1 $((replicas_count - 1))); do
    reordered_replicas_csv+="${replicas_array[$i]},"
  done
  reordered_replicas_csv+="$current_preferred_leader"
  $REASSIGN --zookeeper "$ZOOKEEPER" --topic "$TOPIC" --partition "$PARTITION" --replicas "$reordered_replicas_csv"
fi

if [ "$current_leader_node" != "$NODE_TO_DEMOTE" ]; then
  exit 0
fi

echo "Forcing preferred leader election for $TOPIC-$PARTITION"
JSON="/tmp/$TOPIC-$PARTITION-elect-preferred-leader.json"
cat <<EOF > "$JSON"
{"partitions":[{"topic": "$TOPIC","partition": $PARTITION}]}
EOF
$ELECT_PREFERRED_LEADER --zookeeper "$ZOOKEEPER" --path-to-json-file "$JSON"

sleep 2
# now check status
describe
if [ "$current_leader_node" = "$NODE_TO_DEMOTE" ]; then
  echo "Failed to demote leader node $NODE_TO_DEMOTE for $TOPIC-$PARTITION"
  exit 1
fi