feat: keys example

README.md

@@ -52,3 +52,22 @@ If you create more consumers than paritions, the extra consumers will be idle.
 There is no scaling down of partitions, to decrease partitions, you need to create a new topic with less partitions and migrate data over.
 
 # 04-keys
+
+If I want to have all messages for a certain user to always go in the same partition, I can use keys.
+Example: if messages for the user MUST be processed in order.
+
+Change the container name and the topic
+
+```
+sudo chown -R 1000:1000 kafka-data
+
+sudo docker exec kafka-keys /opt/kafka/bin/kafka-topics.sh --create --topic keys-topic --partitions 2 --bootstrap-server localhost:9092
+```
+
+If you forget to run the above command to create the topic, the topic will be created automatically when the producer sends the first message. But it will have only 1 partition by default.
+
+DELETE topic:
+
+```
+docker exec -it kafka-keys /opt/kafka/bin/kafka-topics.sh --delete --topic keys-topic --bootstrap-server localhost:9092
+```