# Quickstart: Service Invocation

In this quickstart, you'll run a client and server application on [Catalyst Cloud](https://docs.diagrid.io/operate/hosting/catalyst-cloud). You will learn how to:

- Provision a Catalyst project with apps for two applications using the Diagrid CLI.
- Invoke a remote service method from a client application using the Dapr Service Invocation API.
- Verify successful service-to-service communication in the application logs and the Catalyst web console.

```mermaid
---
title: Client and Server Apps connected via Catalyst Service Invocation
---
flowchart LR
  APP1(Client App)
  subgraph Catalyst
    APPID1(ID: client)
    APPID2(ID: server)
  end
  APP2(Server App)
  APP1-->APPID1
  APPID1-->APPID2
  APPID2-->APP2
```

## 1. Prerequisites

Before you proceed, ensure you have the following prerequisites installed.

**Python**

- [Diagrid Catalyst account](https://catalyst.diagrid.io/)
- [Diagrid CLI](https://docs.diagrid.io/getting-started/install-cli)
- [Git](https://git-scm.com/downloads)
- [Python 3.12+](https://www.python.org/downloads/) & [uv](https://docs.astral.sh/uv/#installation)

**.NET**

- [Diagrid Catalyst account](https://catalyst.diagrid.io/)
- [Diagrid CLI](https://docs.diagrid.io/getting-started/install-cli)
- [Git](https://git-scm.com/downloads)
- [.NET 10.0](https://dotnet.microsoft.com/en-us/download)

**JavaScript**

- [Diagrid Catalyst account](https://catalyst.diagrid.io/)
- [Diagrid CLI](https://docs.diagrid.io/getting-started/install-cli)
- [Git](https://git-scm.com/downloads)
- [Node.JS LTS](https://nodejs.org/en/)

**Java**

- [Diagrid Catalyst account](https://catalyst.diagrid.io/)
- [Diagrid CLI](https://docs.diagrid.io/getting-started/install-cli)
- [Git](https://git-scm.com/downloads)
- Java 17+: [OracleJDK](https://www.oracle.com/java/technologies/downloads/) or [OpenJDK](https://jdk.java.net/)
- [Apache Maven 3.9.5+](https://maven.apache.org/download.cgi)

## 2. Log in to Catalyst

Authenticate to Diagrid Catalyst using the following command:

```bash
diagrid login
```

This command opens a new browser window where you'll be shown a confirmation code that should match the code in your terminal.
Confirm the code, and if you're not logged into Catalyst, you'll be redirected to login.

Confirm your user details are correct using the following command:

```bash
diagrid whoami
```

The expected output contains the name of the organization, your user name, and the Catalyst API endpoint.

## 3. Clone Quickstart Code

Clone the quickstart code from GitHub:

```bash
git clone https://github.com/diagridio/catalyst-quickstarts
```

Navigate to the quickstart directory:

**Python**

**macOS/Linux**

```bash
cd catalyst-quickstarts/invocation/python
```

**Windows**

```powershell
cd catalyst-quickstarts\invocation\python
```

**.NET**

**macOS/Linux**

```bash
cd catalyst-quickstarts/invocation/csharp
```

**Windows**

```powershell
cd catalyst-quickstarts\invocation\csharp
```

**JavaScript**

**macOS/Linux**

```bash
cd catalyst-quickstarts/invocation/javascript
```

**Windows**

```powershell
cd catalyst-quickstarts\invocation\javascript
```

**Java**

**macOS/Linux**

```bash
cd catalyst-quickstarts/invocation/java
```

**Windows**

```powershell
cd catalyst-quickstarts\invocation\java
```

## 4. Install Dependencies

Install the dependencies for both the client and server applications.

**Python**

Install Python dependencies:

```bash
uv sync --all-packages
```

**.NET**

Install .NET dependencies:

```bash
dotnet restore ./client && dotnet restore ./server
```

**JavaScript**

Install Node dependencies:

```bash
npm install --prefix ./client && npm install --prefix ./server
```

**Java**

Install Maven dependencies:

```bash
mvn clean install -f ./client && mvn clean install -f ./server
```

## 5. Run the application with Catalyst Cloud

The `diagrid dev run` command creates your Catalyst project, provisions resources (apps), configures environment variables, and launches your application connected to Catalyst Cloud.

**Python**

```bash
uv run diagrid dev run -f invocation-quickstart.yaml --project invocation-quickstart --approve
```

**.NET**

```bash
diagrid dev run -f invocation-quickstart.yaml --project invocation-quickstart --approve
```

**JavaScript**

```bash
diagrid dev run -f invocation-quickstart.yaml --project invocation-quickstart --approve
```

**Java**

```bash
diagrid dev run -f invocation-quickstart.yaml --project invocation-quickstart --approve
```

:::tip
Wait a few seconds until you see the log `Connected App ID "server" to http://localhost:5002` in the terminal before proceeding to ensure both applications are up and running.
:::

## 6. Invoke the service

With the quickstart running, test the Service Invocation API by sending a request from the client app to the server app.

### 6.1 Send a request

Open a new terminal and execute the following command to invoke the server app through the client app:

**macOS/Linux**

```bash
curl -i -X POST http://localhost:5001/order -H "Content-Type: application/json" -d '{"orderId":1}'
```

**Windows**

```powershell
Invoke-RestMethod -Method Post -Uri "http://localhost:5001/order" -ContentType "application/json" -Body '{"orderId":1}'
```

The expected response is `200 OK` with this body:

```json
{"message":"Invocation successful","orderId":1,"targetApp":"server"}
```

In the `diagrid dev run` terminal, the server app logs should indicate the request was successfully received, and the client app logs should show the invocation was successful.

### 6.2 View in the Catalyst web console

Open the [Catalyst Cloud web console](https://catalyst.diagrid.io/call-graph) and navigate to the Topology section that visualizes the communication between the `client` and `server` applications.

## 7. Clean Up

Press CTRL+C in the terminal that runs `diagrid dev run` to stop the application and disconnect from Catalyst Cloud.

To delete the entire project and all provisioned resources:

```bash
diagrid project delete invocation-quickstart
```

## Summary

In this quickstart you:

- Logged in to Catalyst and provisioned a managed service invocation project with a single CLI command (`diagrid dev run`).
- Invoked a remote server method from a client application using the Dapr Service Invocation API.
- Verified service-to-service communication through application logs and the Catalyst web console.

Catalyst handled service discovery, routing, and secure communication automatically — no infrastructure to manage.

## Next steps

- Explore the [Dapr API SDK guides](https://docs.diagrid.io/develop/dapr-apis) to integrate service invocation into your own applications.
- Try the [Pub/Sub quickstart](https://docs.diagrid.io/getting-started/quickstarts/dapr-apis/pubsub) to add event-driven messaging between your services.