Why is my app timing out even though PostgreSQL is up?

If PostgreSQL is “up” but your app is timing out, the problem is usually connectivity, authentication, or server-side overload, not whether the database process is running.

Common causes:

• Wrong host/port from the app

  • App may be pointing at localhost when Postgres is in another container/VM.
  • Port mapping may be incorrect.

• Network/firewall/security group issue

  • DB is running, but traffic from the app can’t reach it.
  • Docker/Kubernetes/VPC firewall rules may block the connection.

• PostgreSQL not actually accepting remote connections

  • listen_addresses may be too restrictive.
  • pg_hba.conf may reject the app’s IP/user/database.

• Too many connections / connection pool exhaustion

  • PostgreSQL is alive but has no free connections.
  • App waits until timeout trying to get a connection.

• Slow queries or locks

  • The app connects, but its query blocks on a lock or runs too slowly.
  • This can look like a timeout even though the DB is healthy.

• DNS or service discovery problems

  • The hostname resolves slowly or to the wrong IP.

• SSL/TLS mismatch

  • App expects SSL but server doesn’t, or vice versa.

• Application-side timeout too low

  • The DB is reachable, but startup/query timeout is shorter than connection establishment.

Quick checks:

1. From the app host/container, try:

   psql -h <db-host> -p 5432 -U <user> -d <db>
   

2. Check PostgreSQL logs for rejected connections or authentication failures.
3. Verify:
   • listen_addresses
   • pg_hba.conf
   • firewall/security rules
4. Check active connections and locks:

   SELECT * FROM pg_stat_activity;
   

5. Confirm your app’s DB hostname/port/user/password/SSL settings.

If you want, paste:

• the app’s connection string,
• where Postgres is running (local, Docker, Kubernetes, cloud),
• and the exact timeout/error message,

and I can help narrow it down quickly.