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.NET¶

In this tutorial, you will run a .NET client application that produces messages to and consumes messages from an Apache Kafka® cluster.

After you run the tutorial, view the provided source code and use it as a reference to develop your own Kafka client application.

Prerequisites¶

Client¶

.NET Core 2.1 or higher to run the client application
On Windows, default trusted root CA certificates are stored in the Windows Registry. These are required for secure access to Confluent Cloud. The .NET library does not currently have the capability to access these certificates, so you must obtain them from somewhere else, for example use the cacert.pem file distributed with curl (download cacert.pm).

Kafka Cluster¶

You can use this tutorial with a Kafka cluster in any environment:
- In Confluent Cloud
- On your local host
- Any remote Kafka cluster
If you are running on Confluent Cloud, you must have access to a Confluent Cloud cluster
- The first 20 users to sign up for Confluent Cloud and use promo code C50INTEG will receive an additional $50 free usage (details)

Setup¶

Clone the confluentinc/examples GitHub repository and check out the 5.5.15-post branch.

git clone https://github.com/confluentinc/examples
cd examples
git checkout 5.5.15-post

Change directory to the example for .NET.
```
cd clients/cloud/csharp/
```
Create a local file (for example, at $HOME/.confluent/librdkafka.config) with configuration parameters to connect to your Kafka cluster. Starting with one of the templates below, customize the file with connection information to your cluster. Substitute your values for {{ BROKER_ENDPOINT }}, {{CLUSTER_API_KEY }}, and {{ CLUSTER_API_SECRET }} (see Connecting Clients to Confluent Cloud for instructions on how to create or find those values).
- Template configuration file for Confluent Cloud
```
# Kafka
bootstrap.servers={{ BROKER_ENDPOINT }}
security.protocol=SASL_SSL
sasl.mechanisms=PLAIN
sasl.username={{ CLUSTER_API_KEY }}
sasl.password={{ CLUSTER_API_SECRET }}
```
- Template configuration file for local host
```
# Kafka
bootstrap.servers=localhost:9092
```

Basic Producer and Consumer¶

In this example, the producer application writes Kafka data to a topic in your Kafka cluster. If the topic does not already exist in your Kafka cluster, the producer application will use the Kafka Admin Client API to create the topic. Each record written to Kafka has a key representing a username (for example, alice) and a value of a count, formatted as json (for example, {"count": 0}). The consumer application reads the same Kafka topic and keeps a rolling sum of the count as it processes each record.

Produce Records¶

Build the client example application
```
dotnet build
```
Run the example application, passing in arguments for:
- whether to produce or consume (produce)
- the topic name
- the local file with configuration parameters to connect to your Kafka cluster
- Windows only: a local file with default trusted root CA certificates.
```
# Run the producer (Windows)
dotnet run produce test1 $HOME/.confluent/librdkafka.config /path/to/curl/cacert.pem

# Run the producer (other)
dotnet run produce test1 $HOME/.confluent/librdkafka.config
```

Verify that the producer sent all the messages. You should see:

Producing record: alice {"count":0}
Producing record: alice {"count":1}
Producing record: alice {"count":2}
Producing record: alice {"count":3}
Producing record: alice {"count":4}
Producing record: alice {"count":5}
Producing record: alice {"count":6}
Producing record: alice {"count":7}
Producing record: alice {"count":8}
Producing record: alice {"count":9}
Produced record to topic test1 partition [0] @ offset 0
Produced record to topic test1 partition [0] @ offset 1
Produced record to topic test1 partition [0] @ offset 2
Produced record to topic test1 partition [0] @ offset 3
Produced record to topic test1 partition [0] @ offset 4
Produced record to topic test1 partition [0] @ offset 5
Produced record to topic test1 partition [0] @ offset 6
Produced record to topic test1 partition [0] @ offset 7
Produced record to topic test1 partition [0] @ offset 8
Produced record to topic test1 partition [0] @ offset 9
10 messages were produced to topic test1

View the producer code.

Consume Records¶

Run the example application, passing in arguments for:
- whether to produce or consume (consume)
- the topic name: same topic name as used above
- the local file with configuration parameters to connect to your Kafka cluster
- Windows only: a local file with default trusted root CA certificates.
```
# Run the consumer (Windows)
dotnet run consume test1 $HOME/.confluent/librdkafka.config /path/to/curl/cacert.pem

# Run the consumer (other)
dotnet run consume test1 $HOME/.confluent/librdkafka.config
```

Verify that the consumer sent all the messages. You should see:

Consumed record with key alice and value {"count":0}, and updated total count to 0
Consumed record with key alice and value {"count":1}, and updated total count to 1
Consumed record with key alice and value {"count":2}, and updated total count to 3
Consumed record with key alice and value {"count":3}, and updated total count to 6
Consumed record with key alice and value {"count":4}, and updated total count to 10
Consumed record with key alice and value {"count":5}, and updated total count to 15
Consumed record with key alice and value {"count":6}, and updated total count to 21
Consumed record with key alice and value {"count":7}, and updated total count to 28
Consumed record with key alice and value {"count":8}, and updated total count to 36
Consumed record with key alice and value {"count":9}, and updated total count to 45

When you are done, press <ctrl>-c.
View the consumer code.