Deploying a React application to Microsoft Azure appears straightforward, but hidden complexities exist. This guide focuses on deploying create-react-app (or similar front-end frameworks using pushState routing) to Azure, minimizing client-server routing conflicts.

A brief anecdote illustrates the challenges: In a previous project with a React front-end and ASP.NET Core back-end deployed separately to Azure, page refreshes resulted in 404 errors due to routing misconfigurations. This highlighted the need for proper server-side configuration to handle client-side routing.

Production-Ready React Builds

Building a React app for production (using npm run build) creates an optimized build folder containing static assets. Deploying this folder to a server is sufficient for a live application. The structure typically resembles:

<code>→ build
  → static
    → css
      → css files
    → js
      → js files
    → media
      → media files
  → index.html
  → other files...</code>

Client-Side Routing with React Router

React Router leverages the HTML5 pushState API. PushState updates the URL without a full page reload, enabling client-side routing. However, this presents challenges when deploying to a server. A standard server expects to find files matching the URL path; with client-side routing, this isn't the case. The server must be configured to serve index.html for all routes.

Express.js, for example, requires this configuration:

app.get('*', (req, res) => {
  res.sendFile(path.resolve(__dirname, 'client', 'build', 'index.html'));
});

This assumes the React app is hosted at the server root. For separate front-end and back-end projects, this approach is problematic. Since we're deploying a static app, a back-end isn't strictly necessary.

Azure App Service Deployment

To deploy to Azure:

1. Create a new App Service in the Azure portal.
2. Navigate to the Deployment Center. We'll use Local Git with Kudu as the build provider.
3. Azure provides a Git remote URL; clone this locally.
4. After building the React app (npm run build), initialize a Git repository in the build folder, commit changes, and push to the Azure remote.

Crucially, ensure your package.json specifies a supported Node.js version for Azure (check available versions using az webapp list-runtimes). Add a line like "engines": {"node": "10.0"}.

The initial deployment may fail on page refreshes due to the 404 error.

Reconciling Client-Server Routing in Azure

To resolve this, add a web.config file to the build folder:

<?xml version="1.0"?>
<configuration>
  <system.webserver>
    <rewrite>
      <rules>
        <rule name="React Routes" stopprocessing="true">
          <match url=".*"></match>
          <conditions logicalgrouping="MatchAll">
            <add input="{REQUEST_FILENAME}" matchtype="IsFile" negate="true"></add>
            <add input="{REQUEST_FILENAME}" matchtype="IsDirectory" negate="true"></add>
            <add input="{REQUEST_URI}" negate="true" pattern="^/(api)"></add>
          </conditions>
          <action type="Rewrite" url="/"></action>
        </rule>
      </rules>
    </rewrite>
  </system.webserver>
</configuration>

Rebuild and redeploy. The application should now function correctly. For continuous deployment, explore Azure's continuous integration/continuous deployment (CI/CD) features.

Conclusion

Azure offers robust capabilities for deploying React applications. Understanding client-server routing interactions is key to successful deployments. Further resources on Kudu, Node.js deployment, and static site deployment on Azure are recommended for deeper understanding.

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