My Spring Boot backend cannot connect to MySQL via internal networking. Connection times out after ~30 seconds. Public URL works fine.

Environment:

- Region: EU West (Amsterdam) — both services

- Backend: Spring Boot 3.4.6, Java 17, MariaDB JDBC driver

- Database: Railway MySQL

- Both services show "Online" status

Timeline:

- Working: ~4 hours ago

- Broken: After a routine git push (only changed a markdown file, no config changes)

What I Tested:

- Public URL works: jdbc:mariadb://turntable.proxy.rlwy.net:24191/railway

- Internal URL times out: jdbc:mariadb://mysql.railway.internal:3306/railway

- Reference variable times out: ${{MySQL.RAILWAY_PRIVATE_DOMAIN}}:3306

Error log:

- Socket fail to connect to address=(host=mysql.railway.internal)(port=3306)(type=primary). Connect timed out org.hibernate.exception.JDBCConnectionException: unable to obtain isolated JDBC connection

Steps to Reproduce:

1. Deploy backend with DATABASE_URL using mysql.railway.internal

2. Backend fails to start — connection timeout after ~30 seconds

3. Change DATABASE_URL to public proxy URL

4. Backend starts successfully

Expected:

- Internal networking should allow connection between services in the same project/region.

I am currently using public URL, but need internal networking for lower latency.

Thanks