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Circuit breaker is a design pattern in modern software development.
Circuit breaker is used to detect failures and encapsulates logic of preventing a failure to reoccur constantly (during maintenance, temporary external system failure or unexpected system difficulties).
Common Uses
Your application connects to a database 100 times per second and the database fails. You do not want to have the same error reoccur constantly. You also want to handle the error quickly and gracefully without waiting for TCP connection timeout.
Circuit breaker is used to detect failures and prevent application from trying to perform the action that is doomed to fail (until its safe to retry).
Example Implementation
PHP
The following is a POC example implementation in PHP.
Check
The following script could be run on a set interval through crontab.
$db = mysql_connect('localhost','root','pass');
if ($db === false) {
apc_store('dbUp', 'up');
} else {
apc_store('dbUp', 'down');
@mysql_close($db);
}
Usage in an application
if (apc_fetch('dbUp') === 'down') {
echo "The database server is currently not available. Please try again in a minute.";
exit;
}
$db = mysql_connect('localhost', 'root', 'pass');
$res = mysql_db_query('database', 'SELECT * FROM table');