refactor(galeracheck)

Author: tanji

galeracheck/README.md

@@ -0,0 +1,220 @@
+# galeracheck
+
+HTTP health check service for Galera Cluster nodes. Returns HTTP 200 or 503 based on node state for use with load balancers (HAProxy, AWS ELB, etc.).
+
+## Overview
+
+galeracheck is a lightweight HTTP service that monitors the health of a Galera Cluster node and reports its availability status. Load balancers can poll this endpoint to determine whether to route traffic to the node.
+
+## Installation
+
+```bash
+go build
+sudo cp galeracheck /usr/local/bin/
+```
+
+### Systemd Service
+
+```bash
+sudo cp galeracheck.service /etc/systemd/system/
+sudo systemctl daemon-reload
+sudo systemctl enable galeracheck
+sudo systemctl start galeracheck
+```
+
+## Usage
+
+```bash
+galeracheck [options]
+```
+
+### Options
+
+```
+-config string
+    MySQL config file to use (default "~/.my.cnf")
+
+-port int
+    TCP port to listen on (default 8000)
+
+-mysql-socket string
+    Path to unix socket of monitored MySQL instance (default "/run/mysqld/mysqld.sock")
+
+-mysql-host string
+    Hostname or IP address of monitored MySQL instance (default: use unix socket)
+
+-mysql-port string
+    Port of monitored MySQL instance (default "3306")
+
+-available-when-donor
+    Keep node available in LB when in donor state (state 2)
+    Useful during RSU (Rolling Schema Upgrade) operations
+
+-disable-when-readonly
+    Remove node from LB when read_only is set
+    Useful for gracefully taking a node out of rotation
+```
+
+## Configuration
+
+Create a MySQL config file (default `~/.my.cnf`) with credentials:
+
+```ini
+[mysql]
+user=monitor
+password=secret
+socket=/run/mysqld/mysqld.sock
+```
+
+Or for TCP connections:
+
+```ini
+[mysql]
+user=monitor
+password=secret
+host=localhost
+port=3306
+```
+
+The `[client]` section is also supported if `[mysql]` is not present.
+
+## MySQL User Privileges
+
+The monitoring user needs minimal privileges:
+
+```sql
+CREATE USER 'monitor'@'localhost' IDENTIFIED BY 'secret';
+GRANT PROCESS ON *.* TO 'monitor'@'localhost';
+FLUSH PRIVILEGES;
+```
+
+## Health Check Logic
+
+The service queries the following Galera status variables:
+- `wsrep_local_state` - Node's current state
+- `wsrep_cluster_size` - Number of nodes in cluster
+- `read_only` (when `-disable-when-readonly` is used)
+
+### Node States
+
+- **State 4 (Synced)**: Node is synchronized and operational
+- **State 2 (Donor/Desynced)**: Node is acting as donor for SST/IST or in RSU mode
+
+### Availability Rules
+
+The service returns **HTTP 200** (available) when:
+1. Node is in state 4 (Synced)
+2. OR `-available-when-donor` is enabled AND node is in state 2
+3. OR `-disable-when-readonly` is enabled AND read_only is OFF AND state is 4
+4. **OR cluster size is 1 AND state is 4** (failsafe for last remaining node)
+
+Otherwise, returns **HTTP 503** (unavailable).
+
+### Single-Node Failsafe
+
+When the cluster degrades to a single node (`wsrep_cluster_size = 1`), that node remains available even without `-available-when-donor` enabled. This prevents complete service outage in degraded cluster scenarios.
+
+## Load Balancer Integration
+
+### HAProxy Example
+
+```
+backend galera_cluster
+    mode tcp
+    balance leastconn
+    option httpchk
+
+    server node1 10.0.1.11:3306 check port 8000
+    server node2 10.0.1.12:3306 check port 8000
+    server node3 10.0.1.13:3306 check port 8000
+```
+
+### AWS Application Load Balancer
+
+Configure health check:
+- Protocol: HTTP
+- Port: 8000
+- Path: /
+- Success codes: 200
+
+## Use Cases
+
+### Standard Deployment
+
+```bash
+galeracheck -port 8000
+```
+
+Nodes in state 4 (Synced) are available. Donor nodes (state 2) are removed from LB.
+
+### Rolling Schema Upgrade (RSU)
+
+```bash
+galeracheck -port 8000 -available-when-donor
+```
+
+Nodes remain available during RSU DDL operations (when in state 2).
+
+### Graceful Node Removal
+
+```bash
+galeracheck -port 8000 -disable-when-readonly
+```
+
+Set `read_only=ON` on a node to remove it from the LB without triggering desync.
+
+### TCP Connection
+
+```bash
+galeracheck -port 8000 -mysql-host 127.0.0.1 -mysql-port 3306
+```
+
+Monitor via TCP instead of unix socket.
+
+## Response Format
+
+**Available (HTTP 200)**
+```
+200 Galera Node is synced
+```
+
+**Unavailable (HTTP 503)**
+```
+503 Galera Node is not synced
+```
+
+**Connection Error (HTTP 503)**
+```
+503 No connection
+```
+
+**Query Error (HTTP 503)**
+```
+503 Cannot check cluster state: <error>
+```
+
+## Troubleshooting
+
+### Connection Issues
+
+Check MySQL credentials and socket/host configuration:
+```bash
+mysql --defaults-file=~/.my.cnf -e "SHOW STATUS LIKE 'wsrep%';"
+```
+
+### Permission Issues
+
+Verify the monitoring user has PROCESS privilege:
+```sql
+SHOW GRANTS FOR 'monitor'@'localhost';
+```
+
+### Service Logs
+
+```bash
+sudo journalctl -u galeracheck -f
+```
+
+## License
+
+See parent project license.

galeracheck/galeracheck.go

@@ -3,7 +3,7 @@ Description=Galera Check Service
 
 [Service]
 Type=simple
-ExecStart=/usr/local/bin/galeracheck -a -p 8000
+ExecStart=/usr/local/bin/galeracheck -port 8000
 Restart=on-failure
 
 [Install]