Addressing MySQL Error 2025 – (CR_PROBE_MASTER_CONNECT) When Connecting to Master Server

If you’re working with MySQL replication and encounter Error 2025 – (CR_PROBE_MASTER_CONNECT), it indicates a problem with connecting to the master server. This error can be due to various reasons such as network issues, incorrect configuration settings, or authentication problems. In this post, we’ll explore how to pinpoint the cause of this error and implement solutions to resolve it.

Understanding the Error

Error 2025 occurs when a replica server is unable to establish a connection to the master server. This connection is essential for replication as it allows the replica to receive binary log events from the master.

Diagnosing the Error

To diagnose the issue, consider the following steps:

  1. Check Network Connectivity: Verify that the replica can reach the master server over the network. Use tools like ping and telnet to test connectivity to the master server’s IP address and MySQL port (default 3306).
  2. Review Replication Settings: Inspect the replication configuration settings in the my.cnf or my.ini file on the replica server. Ensure that the master_host, master_user, master_password, and master_port settings are correct.
  3. Verify Master Server Settings: On the master server, check the bind-address and ensure it’s configured to accept connections from the replica server. Also, verify that the user specified in the master_user setting has the necessary replication privileges.
  4. Check Firewall Rules: Ensure that any firewalls between the replica and master servers allow traffic on the MySQL port.
  5. Examine Error Logs: Review the MySQL error logs on both the master and replica servers for additional clues about the connection failure.

Fixing the Error

Here are some examples and sample code to help you resolve MySQL Error 2025:

Example 1: Testing Network Connectivity

Test if the replica server can reach the master:

ping master_server_ip
telnet master_server_ip 3306

If these commands fail, there is a network connectivity issue that needs to be resolved.

Example 2: Configuring Replication Settings

Ensure the replication settings on the replica server are correct:

# my.cnf or my.ini on the replica server


relay-log = /var/lib/mysql/mysql-relay-bin.log log_bin = /var/lib/mysql/mysql-bin.log server-id = 2 read_only = 1 master_host = master_server_ip master_user = replication_user master_password = replication_password master_port = 3306

Replace master_server_ip, replication_user, and replication_password with the correct values for your setup.

Example 3: Granting Replication Privileges

On the master server, create a user for replication and grant the necessary privileges:

CREATE USER 'replication_user'@'replica_server_ip' IDENTIFIED BY 'replication_password';
GRANT REPLICATION SLAVE ON *.* TO 'replication_user'@'replica_server_ip';

Replace replica_server_ip, replication_user, and replication_password with the appropriate values.

Example 4: Adjusting Firewall Settings

Adjust the firewall settings to allow traffic from the replica server to the master server on the MySQL port.

Example 5: Reviewing Error Logs

Check the MySQL error logs on both servers for detailed error messages that can help identify the problem:

# On Unix/Linux systems
cat /var/log/mysql/error.log

# On Windows systems
type C:\ProgramData\MySQL\MySQL Server x.x\Data\hostname.err

By following these steps, you should be able to diagnose and fix Error 2025, establishing a successful connection between your replica and master MySQL servers. Ensure that you carefully apply the changes and monitor the replication process after resolving the issue to confirm that it is functioning correctly. If the problem persists, consider seeking assistance from MySQL support channels or a database administrator with expertise in MySQL replication.

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