kafka: how to rebalance parititions between brokers

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+
+## Rebalance Storage Between Brokers
+
+For example, after adding or removing brokers from the cluster.
+
+Create a list of topics to move, and put it in `/tmp/topics_to_move.json`:
+
+    {
+      "version": 1,
+      "topics": [
+        {"topic": "sandcrawler-shadow.grobid-output"},
+        {"topic": "fatcat-prod.api-crossref"}
+      ]
+    }
+
+On a kafka broker, go to `/srv/kafka-broker/kafka-*/bin`, generate a plan, then
+inspect the output:
+
+    ./kafka-reassign-partitions.sh --zookeeper localhost:2181 --broker-list "280,281,284,285,263" --topics-to-move-json-file /tmp/topics_to_move.json --generate > /tmp/reassignment-plan.json
+    cat /tmp/reassignment-plan.json | rg '^\{' | tail -n1 > /tmp/new-plan.json
+    cat /tmp/reassignment-plan.json | rg '^\{' | jq .
+
+If that looks good, start the rebalance:
+
+    ./kafka-reassign-partitions.sh --zookeeper localhost:2181 --reassignment-json-file /tmp/new-plan.json --execute
+
+Then monitor progress:
+
+    ./kafka-reassign-partitions.sh --zookeeper localhost:2181 --reassignment-json-file /tmp/new-plan.json --verify