App Service Application Error 🔷 Azure

Azure App Service: ":( Application Error" / container didn’t respond to HTTP pings

App Service started your app but it crashed or never listened on the expected port.

Seen on: Azure Node.js

Meaning

On Linux App Service, the platform pings your container on the port in WEBSITES_PORT (default 80/8080). If the app listens elsewhere, crashes on startup, or takes too long, you get “Application Error”.

Common causes

  • App listens on a different port than WEBSITES_PORT
  • Startup crash (missing app settings / connection strings)
  • Wrong startup command or entry point
  • Startup slower than the container start time limit
  • Dependencies not installed during build (SCM_DO_BUILD_DURING_DEPLOYMENT)

⚡ Quick fix

  1. Check Log stream / Diagnose and solve problems
  2. Listen on process.env.PORT (Node) or set WEBSITES_PORT
  3. Verify app settings exist in this slot
  4. Increase WEBSITES_CONTAINER_START_TIME_LIMIT for slow starts

Detailed fix by platform

Azure

  1. Stream logs and set the port:
    bash
    az webapp log tail -n my-app -g my-rg
az webapp config appsettings set -n my-app -g my-rg --settings WEBSITES_PORT=3000

Node.js

  1. app.listen(process.env.PORT || 3000) — never hard-code the port on App Service.

How to diagnose

  1. Logs — What does the container log show at startup?
  2. Port — Which port does the app listen on?
  3. Settings — Required env vars present in this slot?

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