# Variables & Secrets

{% hint style="warning" %}
To execute K2K, you must agree to the EULA and secure a free license.

Accept the EULA by setting `license.acceptEula` to `true` .
{% endhint %}

K2K enables the inclusion of variables in the replication definition, allowing secrets to be injected at runtime without being embedded directly in the pipeline definition. See [variables-and-secrets](https://docs.lenses.io/latest/k2k/configuration/variables-and-secrets "mention") for more details.

This tutorial assumes the following files exist (See [run-a-quick-example](https://docs.lenses.io/latest/k2k/tutorial/run-a-quick-example "mention") for more details):

{% tabs %}
{% tab title="k2k-pipeline.yml" %}

```yaml
name: "my-first-replication"
features:
  autoCreateControlTopics: enabled
  autoCreateTopics: enabled
source:
  kafka:
    common:
      "bootstrap.servers": "kafka-source:9092"
    consumer:
      "group.id": "k2k.my-first-k2k"
target:
  kafka:
    common:
      "bootstrap.servers": "kafka-target:9092"
replication:
  - source:
      topic: ".*"
  - sink:
      topic: source
      partition: source
```

{% endtab %}

{% tab title="docker-compose.yml" %}

```yaml
services:
  k2k:
    image: "lensesio/k2k:0.5.0"
    volumes:
      - ".:/pipelines"
    environment:
      OTEL_SERVICE_NAME: "k2k"
      OTEL_METRICS_EXPORTER: none
      OTEL_TRACES_EXPORTER: none
      OTEL_LOGS_EXPORTER: none
      #LENSES_K2K_ACCEPT_EULA: true
    command:
      - k2k
      - start
      - -f
      - /pipelines/k2k-pipeline.yml
      - -t
  kafka-source:
    image: "apache/kafka:3.8.0"
    environment:
      KAFKA_NODE_ID: 1
      KAFKA_PROCESS_ROLES: broker,controller
      KAFKA_LISTENERS: INTERNAL://:9092,EXTERNAL://:9094,CONTROLLER://:9093
      KAFKA_ADVERTISED_LISTENERS: INTERNAL://kafka-source:9092,EXTERNAL://127.0.0.1:9094
      KAFKA_INTER_BROKER_LISTENER_NAME: INTERNAL
      KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: CONTROLLER:PLAINTEXT,INTERNAL:PLAINTEXT,EXTERNAL:PLAINTEXT
      KAFKA_CONTROLLER_LISTENER_NAMES: CONTROLLER
      KAFKA_CONTROLLER_QUORUM_VOTERS: 1@localhost:9093
      KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
      KAFKA_TRANSACTION_STATE_LOG_REPLICATION_FACTOR: 1
      KAFKA_TRANSACTION_STATE_LOG_MIN_ISR: 1
      KAFKA_GROUP_INITIAL_REBALANCE_DELAY_MS: 0
      KAFKA_NUM_PARTITIONS: 3
    ports:
      - "9094:9094"
  kafka-target:
    image: "apache/kafka:3.8.0"
    environment:
      KAFKA_NODE_ID: 1
      KAFKA_PROCESS_ROLES: broker,controller
      KAFKA_LISTENERS: INTERNAL://:9092,EXTERNAL://:9099,CONTROLLER://:9093
      KAFKA_ADVERTISED_LISTENERS: INTERNAL://kafka-target:9092,EXTERNAL://127.0.0.1:9099
      KAFKA_INTER_BROKER_LISTENER_NAME: INTERNAL
      KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: CONTROLLER:PLAINTEXT,INTERNAL:PLAINTEXT,EXTERNAL:PLAINTEXT
      KAFKA_CONTROLLER_LISTENER_NAMES: CONTROLLER
      KAFKA_CONTROLLER_QUORUM_VOTERS: 1@localhost:9093
      KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
      KAFKA_TRANSACTION_STATE_LOG_REPLICATION_FACTOR: 1
      KAFKA_TRANSACTION_STATE_LOG_MIN_ISR: 1
      KAFKA_GROUP_INITIAL_REBALANCE_DELAY_MS: 0
      KAFKA_NUM_PARTITIONS: 3
    ports:
      - 9099:9099
```

{% endtab %}
{% endtabs %}

To ensure a clean start, execute this command to reset any prior configurations from earlier tutorials.

```bash
docker compose down
```

{% stepper %}
{% step %}

### **Define variables in the pipeline definition**

The pipeline file includes two variables that will be substituted when the pipeline is loaded.

```yaml
name: "my-first-replication"
features:
  autoCreateControlTopics: enabled
  autoCreateTopics: enabled
source:
  kafka:
    common:
      "bootstrap.servers": ${TARGET_BROKER_URL}
    consumer:
      "group.id": "k2k.my-first-k2k"
target:
  kafka:
    common:
      "bootstrap.servers": ${env:string:SOURCE_BROKER_URL}
replication:
  - source:
      topic: ".*"
  - sink:
      topic: source
      partition: source
```

{% endstep %}

{% step %}

### Add the environment variables to the docker compose

```yaml
services:
  k2k:
    image: "eu.gcr.io/k8-engine/k2k/k2k:0.0.10-alpha"
    volumes:
      - ".:/pipelines"
    environment:
      OTEL_SERVICE_NAME: "k2k"
      OTEL_METRICS_EXPORTER: none
      OTEL_TRACES_EXPORTER: none
      OTEL_LOGS_EXPORTER: none
      TARGET_BROKER_URL: "kafka-target:9092"
      SOURCE_BROKER_URL: "kafka-source:9092"
    command:
      - k2k
      - start
      - -f
      - /pipelines/k2k-pipeline.yml
      - -t
      - -g 
      - enabled
  kafka-source:
    image: "apache/kafka:3.8.0"
    environment:
      KAFKA_NODE_ID: 1
      KAFKA_PROCESS_ROLES: broker,controller
      KAFKA_LISTENERS: INTERNAL://:9092,EXTERNAL://:9094,CONTROLLER://:9093
      KAFKA_ADVERTISED_LISTENERS: INTERNAL://kafka-source:9092,EXTERNAL://127.0.0.1:9094
      KAFKA_INTER_BROKER_LISTENER_NAME: INTERNAL
      KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: CONTROLLER:PLAINTEXT,INTERNAL:PLAINTEXT,EXTERNAL:PLAINTEXT
      KAFKA_CONTROLLER_LISTENER_NAMES: CONTROLLER
      KAFKA_CONTROLLER_QUORUM_VOTERS: 1@localhost:9093
      KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
      KAFKA_TRANSACTION_STATE_LOG_REPLICATION_FACTOR: 1
      KAFKA_TRANSACTION_STATE_LOG_MIN_ISR: 1
      KAFKA_GROUP_INITIAL_REBALANCE_DELAY_MS: 0
      KAFKA_NUM_PARTITIONS: 3
    ports:
      - "9094:9094"
  kafka-target:
    image: "apache/kafka:3.8.0"
    environment:
      KAFKA_NODE_ID: 1
      KAFKA_PROCESS_ROLES: broker,controller
      KAFKA_LISTENERS: INTERNAL://:9092,EXTERNAL://:9099,CONTROLLER://:9093
      KAFKA_ADVERTISED_LISTENERS: INTERNAL://kafka-target:9092,EXTERNAL://127.0.0.1:9099
      KAFKA_INTER_BROKER_LISTENER_NAME: INTERNAL
      KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: CONTROLLER:PLAINTEXT,INTERNAL:PLAINTEXT,EXTERNAL:PLAINTEXT
      KAFKA_CONTROLLER_LISTENER_NAMES: CONTROLLER
      KAFKA_CONTROLLER_QUORUM_VOTERS: 1@localhost:9093
      KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
      KAFKA_TRANSACTION_STATE_LOG_REPLICATION_FACTOR: 1
      KAFKA_TRANSACTION_STATE_LOG_MIN_ISR: 1
      KAFKA_GROUP_INITIAL_REBALANCE_DELAY_MS: 0
      KAFKA_NUM_PARTITIONS: 3
    ports:
      - 9099:9099
```

{% endstep %}

{% step %}

### Start Kafka Clusters

To start two local Kafka clusters, use this command:

```bash
#start two kafka instances
docker compose up -d kafka-source kafka-target
```

{% endstep %}

{% step %}

### Run K2K

Use the following command to run the K2K replicator app:

<pre class="language-bash"><code class="lang-bash"><strong>#start k2k
</strong>docker compose up k2k
</code></pre>

{% endstep %}
{% endstepper %}