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Added max connection check #2

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2ff1baa
Added max connection check
yazynin May 2, 2019
33b6c37
Formatting fix
yazynin May 2, 2019
caf91ef
Sample systemd unit file
yazynin May 2, 2019
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34 changes: 33 additions & 1 deletion mysqlchk.go
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,8 @@ import "net/http"
var db *sql.DB
var wsrepStmt *sql.Stmt
var readOnlyStmt *sql.Stmt
var maxConnStmt *sql.Stmt
var connUsedStmt *sql.Stmt

var username = flag.String("username", "clustercheckuser", "MySQL Username")
var password = flag.String("password", "clustercheckpassword!", "MySQL Password")
Expand All @@ -32,6 +34,8 @@ func init() {
func checkHandler(w http.ResponseWriter, r *http.Request) {
var fieldName, readOnly string
var wsrepState int
var maxConn int
var connUsed int

if _, err := os.Stat(*forceUpFile); err == nil {
fmt.Fprint(w, "Cluster node OK by manual override\n")
Expand All @@ -43,7 +47,25 @@ func checkHandler(w http.ResponseWriter, r *http.Request) {
return
}

err := wsrepStmt.QueryRow().Scan(&fieldName, &wsrepState)
err := maxConnStmt.QueryRow().Scan(&fieldName, &maxConn)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}

err = connUsedStmt.QueryRow().Scan(&fieldName, &connUsed)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}

if maxConn <= (connUsed + 10) {

@gleamicus gleamicus May 2, 2019

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Let's add runtime flags for this feature. Either one to enable connection count checking and another to set the limit (10 by default), or just a limit (0 by default, meaning the check is disabled).

http.Error(w, "Cluster node is unavailable Max connections", http.StatusServiceUnavailable)
} else {
log.Println("Number of free connections", maxConn-connUsed)
}

err = wsrepStmt.QueryRow().Scan(&fieldName, &wsrepState)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
Expand Down Expand Up @@ -96,6 +118,16 @@ func main() {
log.Fatal(err)
}

maxConnStmt, err = db.Prepare("show variables like 'max_connections'")
if err != nil {
log.Fatal(err)
}

connUsedStmt, err = db.Prepare("show status where variable_name = 'Threads_connected'")
if err != nil {
log.Fatal(err)
}

log.Println("Listening...")
http.HandleFunc("/", checkHandler)
log.Fatal(http.ListenAndServe(fmt.Sprintf("%s:%d", *bindAddr, *bindPort), nil))
Expand Down
10 changes: 10 additions & 0 deletions mysqlchk.service
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Original file line number Diff line number Diff line change
@@ -0,0 +1,10 @@
[Unit]
Description=Mysqlchk check
After=mariadb.service

[Service]
ExecStart=/usr/bin/mysqlchk

@gleamicus gleamicus May 2, 2019

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We should probably have a way to pass arguments to mysqlchk so people can override the default settings. How about using EnvironmentFile and passing something like $MYSQLCHK_ARGS on this line.

We should also drop privileges to nobody or something, there's no reason for this to run as root.

Restart=always

[Install]
WantedBy=multi-user.target