Using VPC with App Services

Question

We have two Apps both in the same VPC (confirmed by viewing them via the VPC dashboard).

The frontend app connects to the backend app via an environment variable which is currently the full DigitalOcean.app URL of the backend app. e.g. https://back-app-3gxb7.ondigitalocean.app/

The Private IP for back-app shows as: 10.124.0.5, so I tried to replace the env var with https://10.124.0.5/ but but my build failed due to not being able to make a connection to the backend. Is there something more I need to do on back-app to allow connections over the private IP?

Bobby · Answer

Hi there, Just to confirm, when you say “frontend app”, is it a static site or a client-side JavaScript app that runs in the browser? If so, it won’t be able to reach your backend through the private VPC IP (10.x.x.x) since those addresses are only accessible inside the platform’s private network. In that case, you’ll need to expose the backend through a public endpoint and have the frontend call that. If both apps are actually backend services deployed on App Platform within the same VPC, then internal routing should work, but the best approach is to group them as service components under the same app. That automatically handles private communication without having to manage IPs manually: You can check out the official guide here:https://docs.digitalocean.com/products/app-platform/how-to/manage-internal-routing/ Could you share a bit more about how the frontend is deployed and how you’re trying to make the connection?

alexdo · Answer

Hi there, worth adding one thing before the component-grouping question gets sorted out: the exact URL you tried, https://10.124.0.5/ , has a separate problem independent of whether the network path works at all. DigitalOcean issues and manages SSL certificates for your app’s actual domains, the ondigitalocean.app URL or any custom domain, never for a raw private IP. There is no valid certificate bound to 10.124.0.5, so an HTTPS request to it will fail TLS validation regardless of VPC connectivity. Since this is private, internal-only traffic anyway, plain http:// against that same IP is the correct form, not https://. That said, App Platform’s documented private networking pattern is by service name, not by IP at all, http://service_name/ on the internal port, which only works for components grouped under one App as Bobby described. Since your setup is two separate Apps sharing a VPC rather than two components of one App, you’re relying on VPC-level IP networking instead of that same-app service-name routing, which is a valid but different mechanism, and worth confirming that distinction since the fix differs depending on which one you’re actually using. One more thing worth isolating specifically since you said the build failed rather than a runtime request: if the frontend is fetching from the backend during the build step itself, for example server-side generation in Next.js, that is a different code path than a runtime API call, and I could not confirm from DigitalOcean’s docs whether build-time processes get the same VPC network access as the running app does. Worth testing whether the same request succeeds once the app is actually running, to isolate whether this is a protocol issue, a same-app-vs-separate-apps routing issue, or a build-time-specific network limitation. Regards

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