Host is not allowed to connect to this MySQL server

What this means

Error 1130 (SQLSTATE HY000) is raised when a client's host does not match any host entry in the mysql.user table for the given username. The server rejects the connection before authentication even begins.

Why it happens

1. 1User account was created with 'user'@'localhost' but the client is connecting from a different IP
2. 2User account uses a specific IP (e.g. 'user'@'192.168.1.10') that does not match the actual client IP
3. 3DNS reverse-lookup failure causes the resolved hostname to differ from the grant
4. 4skip-name-resolve is enabled but the grant uses a hostname instead of an IP

How to reproduce

A client connecting from a host not listed in the user's grant.

-- From a remote machine:
mysql -h db.example.com -u appuser -p
-- appuser only has a grant for 'appuser'@'localhost'

Fix 1: Create or extend the user grant for the correct host

When the client host is known and the connection is intentional.

-- Grant access from a specific IP:
CREATE USER 'appuser'@'203.0.113.45' IDENTIFIED BY 'secret';
GRANT SELECT, INSERT, UPDATE, DELETE ON myapp.* TO 'appuser'@'203.0.113.45';

-- Or use a wildcard for any host (use with care):
CREATE USER 'appuser'@'%' IDENTIFIED BY 'secret';
GRANT SELECT, INSERT ON myapp.* TO 'appuser'@'%';
FLUSH PRIVILEGES;

Fix 2: Enable skip-name-resolve and use IP-based grants

When DNS lookups are slow or unreliable.

-- In my.cnf / server.cnf:
-- [mysqld]
-- skip-name-resolve

-- All grants must then use IP addresses, not hostnames.

What not to do

Dangerous variant

Sources

Confidence assessment

See also