Spring Boot App Fails on Azure App Service – Root Cause and Fix

 A Spring Boot application working perfectly on local or VM environments but failing after deployment to Azure App Service is a very common production issue.

In many cases:

  • The app starts locally without errors

  • The build succeeds

  • Deployment completes successfully

  • ❌ But the application fails to start or crashes on Azure App Service

This blog explains:

  • Why Spring Boot apps fail on Azure App Service

  • The most common root causes

  • Proven fixes used in real production projects

🔴 Common Symptoms

You may observe one or more of the following:

  • App Service shows “Application Error”

  • Continuous restarts

  • HTTP 502 / 503 errors

  • App works locally but not on Azure

  • Logs show startup failure or no logs at all

🧠 Root Causes (Most Important Section)

1️⃣ Incorrect Java Version on Azure App Service

Azure App Service does not always use the same Java version as your local machine.

Example:

  • Local: Java 17

  • Azure App Service: Java 8 or 11

➡️ This causes:

  • Class version errors

  • Unsupported features

  • Startup failure

✅ Fix

In Azure Portal:

  1. Go to Configuration → General settings

  2. Set:

    • Java version (match your build)

    • Java web server (Java SE if using embedded Tomcat)

2️⃣ Port Configuration Issue (Very Common)

Azure App Service exposes the application on port 80 / 443, but Spring Boot may try to run on 8080.

Azure provides the port via environment variable:

WEBSITES_PORT

❌ Problem

Spring Boot listens on a hardcoded port.

✅ Fix

Update application.properties:

server.port=${PORT:8080}

Azure automatically sets PORT.

3️⃣ Missing or Incorrect Startup Command

Azure App Service sometimes fails to detect how to start your JAR.

❌ Problem

No startup command defined.

✅ Fix

Set a startup command:

java -jar app.jar

(Replace app.jar with your actual file name.)

Set this under:
Configuration → General settings → Startup Command

4️⃣ File System Write Failure

Azure App Service uses a read-only file system, except for /home.

❌ Common Mistake

Writing logs or files to:

/tmp
/app
/var

✅ Fix

Write files only to:

/home

Or:

  • Disable file-based logging

  • Use Azure Application Insights

5️⃣ Environment Variables Missing on Azure

Apps often fail because:

  • DB credentials

  • API keys

  • Secrets

are available locally but not configured on Azure.

✅ Fix

Set all required values in:
Configuration → Application settings

Example:

spring.datasource.url=${DB_URL}
spring.datasource.username=${DB_USER}
spring.datasource.password=${DB_PASS}

6️⃣ Spring Profile Mismatch

Azure may start the app using a different profile.

❌ Problem

App expects:

spring.profiles.active=prod

But Azure runs with default profile.

✅ Fix

Set in Azure Application Settings:

SPRING_PROFILES_ACTIVE=prod

🔍 How to Debug Properly on Azure

✔ Enable Application Logs

  • Azure Portal → Monitoring → App Service Logs

  • Enable:

    • Application logging

    • Log level: Information or Error

✔ Use Log Stream

  • Monitor startup logs in real time

  • Identify exact failure point

⚠️ Common Mistakes to Avoid

❌ Hardcoding ports
❌ Assuming local Java version = Azure Java version
❌ Writing files outside /home
❌ Missing environment variables
❌ Not checking Azure startup logs

🏗️ Production Best Practices

  • Always test with Azure-like configuration

  • Externalize all configs

  • Avoid file system dependency

  • Use Application Insights

  • Validate startup command before deployment

🎯 Why This Happens Mostly on Azure App Service

Azure App Service:

  • Is containerized

  • Enforces strict runtime rules

  • Requires explicit configuration

Local success does not guarantee cloud success.

📌 Final Thoughts

A Spring Boot app failing on Azure App Service is rarely a framework bug.
It is almost always caused by:

  • Runtime mismatch

  • Configuration issues

  • Environment assumptions

Once these are fixed, Azure App Service is stable and production ready.

💼 Professional Support Available

If you are facing issues in real projects related to enterprise backend development or workflow automation, I provide paid consulting, production debugging, project support, and focused trainings.

Technologies covered include Java, Spring Boot, PL/SQL, Azure, and workflow automation (jBPM, Camunda BPM, RHPAM).


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