MariaDB 12.3: discovery fails with @@global.read_only scan error ("OFF" into type bool) #120

Bug Report

Orchestrator version

v4.31.1 (official release binary)

Backend

SQLite

Configuration

{
  "Debug": true,
  "ListenAddress": ":3000",
  "MySQLTopologyUser": "orchestrator",
  "MySQLTopologyPassword": "REDACTED",
  "MySQLTopologySSLSkipVerify": true,
  "BackendDB": "sqlite",
  "SQLite3DataFile": "/path/to/orchestrator.sqlite3",
  "MySQLConnectTimeoutSeconds": 2,
  "MySQLConnectionLifetimeSeconds": 300,
  "DefaultInstancePort": 3307,
  "DiscoverByShowSlaveHosts": true,
  "InstancePollSeconds": 5,
  "HostnameResolveMethod": "none",
  "MySQLHostnameResolveMethod": "none",
  "FailureDetectionPeriodBlockMinutes": 1,
  "RecoveryPeriodBlockSeconds": 60,
  "ApplyMySQLPromotionAfterMasterFailover": true,
  "DetachLostSlavesAfterMasterFailover": true
}

Topology

N/A - discovery never succeeds, so the instance never registers and no topology exists for it. orchestrator-client -c topology returns nothing for this host.

Steps to reproduce

1. Stand up a MariaDB 12.3.x server (tested against 12.3.2, official mariadb:12.3 Docker image) with GTID replication configured.
2. Point orchestrator at it: curl -s "http://<orch-host>:3000/api/discover/<mariadb-host>/<port>"
3. Discovery fails immediately; the instance is never added.

Expected behavior

Instance discovers successfully; @@global.read_only is parsed correctly regardless of whether the server returns it as an integer or a string.

Actual behavior

Discovery fails with:

sql: Scan error on column index 4, name "@@global.read_only": sql/driver: couldn't convert "OFF" into type bool

Root cause: on MariaDB 12.3, @@global.read_only is returned over this driver/connector path as the string 'ON'/'OFF' rather than an integer 0/1, and go/inst/instance_dao.go's ReadTopologyInstanceBufferable scans it directly into a bool field, which fails the type conversion.

Confirmed MariaDB-12.x-specific: 11.8.8, 11.4.12, 10.11.18, and MySQL 8.4.11/9.7.2 all return read_only in a form the driver converts fine; only 12.3.2 exhibits this.

Logs

sql: Scan error on column index 4, name "@@global.read_only": sql/driver: couldn't convert "OFF" into type bool

Additional context

• Reproduced consistently across a full multi-version compatibility sweep (MariaDB 10.11/11.4/11.8/12.3, MySQL 8.4/9.7) using fresh containers each time - only 12.3 fails.
• We have a fix and have verified it end-to-end (discovery + full failover cycle + ProxySQL hostgroup handling) against all 6 versions with zero regressions: casting via CASE WHEN CAST(@@global.read_only AS CHAR) IN ('1','ON','on') THEN 1 ELSE 0 END instead of scanning the raw value into bool.
• Branch: fix/mariadb-read-only-bool-scan (will open as a PR).
• Note: a naive CAST(@@global.read_only AS UNSIGNED) approach is not safe - under some MariaDB versions/connector paths this silently evaluates the string 'ON' to 0, which would report a read-only replica as writable. The CASE-WHEN string-match approach avoids this.