nats-requestreply-example

An example of using NATS for request-reply messaging.

This example starts a service that responds with World! from {server id} when it receives a request with the message hello. If you are running multiple service instances, requests will be automatically load-balanced between them.

Background

NATS supports two flavors of request reply messaging: point-to-point or one-to-many. Point-to-point involves the fastest or first to respond. In a one-to-many exchange, you set a limit on the number of responses the requestor may receive.

In a request-response exchange, publish request operation publishes a message with a reply subject expecting a response on that reply subject. You can request to automatically wait for a response inline.

The request creates an inbox and performs a request call with the inbox reply and returns the first reply received. This is optimized in the case of multiple responses.

More information can be found in the NATS Documentation.

Prerequisites

The examples require a local NATS server to be running. To start a NATS server as a Docker container run the following commands:

$ docker pull nats
$ docker run -p 4222:4222 -p 6222:6222 -p 8222:8222 -d --name nats-main nats

Running the Example

Start the Request-Reply Client

You can start the Request-Reply Client using the following command:

$ ./gradlew :requestreply-client:run

Once the client and service is running you will see messages similar to the following in the terminal:

[main] INFO nats.example.requestreply.client.Main - Starting NATS Example Request-Reply Client
[main] INFO nats.example.requestreply.client.Main - SENT: Hello
[main] INFO nats.example.requestreply.client.Main - RECEIVED: World! from 494ad392-e136-4c40-9d1f-69a2d75a5ce6

Start the Request-Reply Service

You can start the Request-Reply Service using the following command:

$ ./gradlew :requestreply-service:run

Once the client and service is running you will see messages similar to the following in the terminal:

[main] INFO nats.example.requestreply.service.Main - Starting NATS Example Request-Reply Service 2c84095d-6a17-4db1-86c3-6d41eb247d9e
[jnats-subscriptions] INFO nats.example.requestreply.service.Main - Received Message From _INBOX.9VgixJvxwVp7Ehi8gej7GJ: Hello
[jnats-subscriptions] INFO nats.example.requestreply.service.Main - Received Message From _INBOX.9VgixJvxwVp7Ehi8gej7IK: Hello
[jnats-subscriptions] INFO nats.example.requestreply.service.Main - Received Message From _INBOX.9VgixJvxwVp7Ehi8gej7KL: Hello

You can start multiple services and see that requests are automatically load-balanced between the instances.

Bugs and Feedback

For bugs, questions and discussions please use the Github Issues.

License

MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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