How to Fix Keycloak LDAP Sync Error

In this tutorial, you'll learn about How to Fix Keycloak LDAP Sync Error. We cover key concepts, practical examples, and best practices.

Keycloak LDAP user federation fails to synchronize users — the sync shows 0 imported or the LDAP connection test fails with Unable to connect to LDAP from the Keycloak admin console.

The Problem

ERROR [org.keycloak.storage.ldap] Failed to sync LDAP users
LDAP connection error: javax.naming.CommunicationException:
localhost:389 [Connection refused (Connection refused)]

Step-by-Step Fix

Step 1: Test LDAP connection from Keycloak server

ldapsearch -H ldap://localhost:389 -D "cn=admin,dc=example,dc=com" -w password -b "dc=example,dc=com"

Step 2: Configure LDAP provider correctly

Vendor: Active Directory / OpenLDAP
Connection URL: ldap://ldap.example.com:389
Users DN: ou=users,dc=example,dc=com
Bind DN: cn=admin,dc=example,dc=com
Bind Credential: ****

Step 3: Set up attribute mapping

Step 4: Configure periodic sync

Import Users: ON
Sync Registrations: ON
Periodic Full Sync: ON — every 86400 seconds
Periodic Changed Users Sync: ON — every 3600 seconds

Step 5: Test synchronization

In the Keycloak admin console, go to User Federation > ldap > Actions > Sync All Users.

Step 6: Check logs

sudo tail -f /opt/keycloak/data/log/server.log | grep -i ldap

Prevention Tips

• Use a dedicated LDAP bind account instead of admin
• Enable STARTTLS or LDAPS for production
• Set realistic sync intervals (hourly for changes, daily for full)
• Monitor LDAP server load during full syncs

Common Mistakes with ldap sync

1. Overlapping type class instances that cause GHC to reject the program with ambiguous dispatch errors
2. Non-exhaustive pattern matches that compile with warnings then crash at runtime
3. Misunderstanding that String is [Char] with poor performance for large text operations

These mistakes appear frequently in real-world KEYCLOAK code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

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