Change replica factor for kafka topics. You need to regenerate and assign all partitions after that if there're more than 1.

gistfile1.txt

#!/bin/bash

topics=__consumer_offsets
new_servers=1,2

while read -r line; do lines+=("$line"); done <<<"$topics"
echo '{"version":1,
  "partitions":[' > topic-expand-plan.json
for t in $topics; do 
    if [ "${t}" == "${lines[-1]}" ]; then
        echo "    {\"topic\":\"${t}\",\"partition\":0,\"replicas\":[$new_servers]}" >> topic-expand-plan.json
    else
        echo "    {\"topic\":\"${t}\",\"partition\":0,\"replicas\":[$new_servers]}," >> topic-expand-plan.json
    fi
done

echo '  ]
}' >> topic-expand-plan.json


~/projects/3/kafka_2.12-2.5.0/bin/kafka-reassign-partitions.sh \
  --zookeeper "z-1.hansonmessagelogs1.k3r2yj.c4.kafka.eu-west-1.amazonaws.com:2181,z-2.hansonmessagelogs1.k3r2yj.c4.kafka.eu-west-1.amazonaws.com:2181,z-3.hansonmessagelogs1.k3r2yj.c4.kafka.eu-west-1.amazonaws.com:2181" \
  --reassignment-json-file topic-expand-plan.json --execute

for t in $topics; do
~/projects/3/kafka_2.12-2.5.0/bin/kafka-topics.sh \
  --zookeeper "z-1.hansonmessagelogs1.k3r2yj.c4.kafka.eu-west-1.amazonaws.com:2181,z-2.hansonmessagelogs1.k3r2yj.c4.kafka.eu-west-1.amazonaws.com:2181,z-3.hansonmessagelogs1.k3r2yj.c4.kafka.eu-west-1.amazonaws.com:2181" \
  --describe --topic ${t}
done