Intermittent 404 with Static Web App Using Custom Domain with Alias Record Set in Azure DNS Zone

Hi Vishvani,

Thanks for your answer. Unfortunately, your answer has not solved my problem.

1. Static Web App Routing and Redirection:

• Ensure that the Static Web App is properly configured to handle redirects from the apex domain to the subdomain. You can configure these redirects in the routes. Json file in the static web app configuration.
• If you're not already, test using a browser and inspect the network traffic to check for any redirect issues or misconfigurations.

I don't actually have any redirects configured in my app. The only redirect is the one performed automatically by Azure when you set a default custom domain. Other custom domains will automatically redirect to the default custom domain.

I also see the 404 errors when I don't set a default custom domain, and there is no automatic redirect. I've only mentioned the redirect because I believe this automatic redirect to the default custom domain happens before the request reaches my app, so this narrows down the issue to being in Azure's infrastructure somewhere instead of in my app.

I'm testing this site with Chrome and cURL. Everything looks correct except for the occasional 404 that occurs about 15% of the time.

2. Alias Record vs. A Record:

• When using an Alias record, ensure that your DNS TTL (Time-to-Live) isn't causing problems. A lower TTL can help, especially during periods of change. Additionally, check if your DNS settings are correctly aligned with the Azure Static Web App requirements. Since the issue doesn't occur with the A record (but disables global distribution), the problem likely lies with the Alias record configuration. It's important to make sure that both your DNS setup and theStatic Web App configuration (especially the custom domain settings) are aligned.

I agree that the issue likely lies with the Alias record configuration or the global distribution, but only for the apex of the domain.

The alias record is automatically created by Azure when I add the custom domain to the static web app. Azure creates the record with a TTL of 1 hour, but I've reduced that to 60 seconds for debugging.

I also created an A record with Alias record set for a subdomain to see if the problem is just that Alias records don't work, but I'm not having any issues with the Alias record for the subdomain. The issue only occurs on the apex of the domain.

3. App Service Scaling or Load Balancing:

• Look at the Azure Static Web App's health and scaling settings. If it's in a region with heavy load or scaling issues, that might cause intermittent availability.

The app is hosted on the Standard hosting plan in the Central US region.

The "Diagnose and solve problems" section in the Azure dashboard doesn't show any issues, and I'm not sure what scaling settings there would be. My understanding is that static web apps don't have any configurable scaling settings because it's essentially just a CDN serving static assets.

Also, wouldn't app health or scaling issue affect all custom domains and the *.azurestaticapps.net domain? I'm only seeing issues with the apex of the domain. The azure domain and other subdomains work perfectly 100% of the time.

4. Azure Static Web App Configuration (Deployment Settings):

• Review your Azure Static Web App's deployment logs for any errors during build or routing. Ensure that your app's routing rules are correctly defined.

I don't have any routing rules configured in my app.

This app is deployed from an Azure DevOps Pipeline, but there are no issues in the pipeline log. I even added a test file and redeployed to confirm the new file show up on the site. The new file does show up, but again I see a 404 error for 15% of requests for that file on the apex domain. I see no 404 errors if I use the azure domain or a subdomain custom domain.

Also, wouldn't deployment errors or routing errors affect the same request 100% of the time? I'm making the same request every time and only see the issue 15% of the time.