# How to change a Kafka topic configuration using the CLI

*Learn how to view and modify topic configurations using kafka-configs in 10 minutes*

While broker-level defaults work for most topics, some require customization. The `kafka-configs` CLI tool lets you override configurations for specific topics without affecting the cluster defaults.

**What you'll learn:**
- How to view current topic configurations
- How to add configuration overrides with kafka-configs
- How to remove configuration overrides
- Common configurations that need per-topic tuning

## Common topic configuration overrides

| Configuration | Default | Description |
|---------------|---------|-------------|
| `min.insync.replicas` | 1 | Minimum ISRs for acks=all |
| `retention.ms` | 7 days | Data retention time |
| `retention.bytes` | -1 (unlimited) | Maximum partition size |
| `cleanup.policy` | delete | delete or compact |
| `max.message.bytes` | 1 MB | Maximum message size |
| `compression.type` | producer | Broker-side compression |

The complete list of topic configurations can be found in the [Kafka documentation](https://kafka.apache.org/documentation/#topicconfigs).

## Override topic configuration defaults

![Broker default min.insync.replicas=1 overridden at the topic level to 2 with kafka-configs --add-config and reverted with --delete-config](https://www.conduktor.io/assets/kafka/diagrams/how-to-change-a-kafka-topic-configuration-using-the-cli.svg)

```mermaid
flowchart LR
    subgraph Broker["Broker Default"]
        BD["min.insync.replicas=1"]
    end

    subgraph Topic["Topic Override"]
        TO["min.insync.replicas=2"]
    end

    BD -->|"kafka-configs --add-config"| TO
    TO -->|"kafka-configs --delete-config"| BD
```

The `kafka-configs` CLI tool allows you to set, view, and delete configurations for topics, brokers, and other entities without restarting the cluster. Use CLI commands with appropriate extensions for your platform (e.g., `kafka-configs.bat` for Windows, `kafka-configs.sh` for Linux).

Let's change the `min.insync.replicas` configuration of a topic. The default broker value is `1`, but for production with replication factor of 3, a value of `2` is recommended. See [min.insync.replicas](https://www.conduktor.io/kafka/kafka-topic-configuration-min-insync-replicas) for details.

Before running Kafka CLIs make sure that you have [started Kafka](https://www.conduktor.io/kafka/starting-kafka) successfully.

First, create a topic named configured-topic with 3 partitions and a replication factor of 1, using Kafka topics CLI, `kafka-topics`

```bash
kafka-topics --bootstrap-server localhost:9092 --create --topic configured-topic --partitions 3 --replication-factor 1
```

Describe the topic to check if there are any configuration override set for this topic.

```bash
kafka-topics --bootstrap-server localhost:9092 --describe --topic configured-topic
```

```
Topic: configured-topic	TopicId: CDU7SBxBQ1mzJGnuH68-cQ	PartitionCount: 3	ReplicationFactor: 1	Configs:
	Topic: configured-topic	Partition: 0	Leader: 2	Replicas: 2	Isr: 2
	Topic: configured-topic	Partition: 1	Leader: 3	Replicas: 3	Isr: 3
	Topic: configured-topic	Partition: 2	Leader: 1	Replicas: 1	Isr: 1
```

There is no configuration override set.

Set the `min.insync.replicas` value for the topic `configured-topic` to 2

```bash
kafka-configs --bootstrap-server localhost:9092 --alter --entity-type topics --entity-name configured-topic --add-config min.insync.replicas=2
```

And describe the topic again

```bash
kafka-topics --bootstrap-server localhost:9092 --describe --topic configured-topic
```

```
Topic: configured-topic	TopicId: CDU7SBxBQ1mzJGnuH68-cQ	PartitionCount: 3	ReplicationFactor: 1	Configs: min.insync.replicas=2
	Topic: configured-topic	Partition: 0	Leader: 2	Replicas: 2	Isr: 2
	Topic: configured-topic	Partition: 1	Leader: 3	Replicas: 3	Isr: 3
	Topic: configured-topic	Partition: 2	Leader: 1	Replicas: 1	Isr: 1
```

Now, you can see there is a topic configuration override set (at the right side of the output) - `min.insync.replicas=2`.

You can delete the configuration override by passing `--delete-config` in place of the `--add-config` flag.

```bash
kafka-configs --bootstrap-server localhost:9092 --alter --entity-type topics --entity-name configured-topic --delete-config min.insync.replicas
```

Describe the topic to make sure the configuration override has been removed.

## Other common configuration changes

### Set retention to 30 days

```bash
kafka-configs --bootstrap-server localhost:9092 --alter \
  --entity-type topics --entity-name configured-topic \
  --add-config retention.ms=2592000000
```

### Enable log compaction

```bash
kafka-configs --bootstrap-server localhost:9092 --alter \
  --entity-type topics --entity-name configured-topic \
  --add-config cleanup.policy=compact
```

### Set multiple configurations at once

```bash
kafka-configs --bootstrap-server localhost:9092 --alter \
  --entity-type topics --entity-name configured-topic \
  --add-config min.insync.replicas=2,retention.ms=604800000
```

Some configuration changes take effect immediately, while others only apply to new data. Test configuration changes in a non-production environment first.

> **See it in practice with Conduktor**
> [Conduktor Console](https://docs.conduktor.io/guide/manage-kafka/kafka-resources/topics) provides a visual interface for viewing and modifying topic configurations. See all overrides at a glance and make changes without memorizing CLI syntax.

## Next steps

- [Send large messages](https://www.conduktor.io/kafka/how-to-send-large-messages-in-apache-kafka) to raise size limits via config
- [Configure min.insync.replicas](https://www.conduktor.io/kafka/kafka-topic-configuration-min-insync-replicas) for durability
- [Set up log retention](https://www.conduktor.io/kafka/kafka-topic-configuration-log-retention) for data lifecycle