Codeigniter alternate database connection if server down - php

Question

I want to use a raw php code in Codeigniter for alternate database connection my raw php code is:
$db = mysql_connect('remote_server', 'username', 'password'); if(!$db){
$db = mysql_connect('localhost', 'username', 'password') ; }
to connect to a backup server if the remote mysql server is down for some reason.
Has anyone done this kind of thing with CodeIgniter? If so, would you mind sharing code or ideas?

Answer 1

UPDATE:
just figured out a better approach.
suppose you have 2 database configuration in database.php, one is the default, the other is the backup
i.e
$db['default']['hostname'] = 'localhost';
$db['default']['username'] = 'root';
$db['default']['password'] = '';
$db['default']['database'] = 'temp_test1';
//.......
$db['backup']=$db['default'];
$db['backup']['hostname'] = 'localhost1';
$db['backup']['username'] = 'root';
$db['backup']['password'] = '';
$db['backup']['database'] = 'temp_test1';
now, add this to the end of the database.php file
//check to see if you can connect
$conn=#mysql_connect($db['default']['hostname'],$db['default']['username'],$db['default']['password']);
if($conn) //check to see if it's connecting, if it is close this connection
{
mysql_close($conn);
}
else{ //if it isnt
$db['default']=$db['backup']; //replace the default credentials with the backup credentials
}
OLD POST:
there are a lot of approaches you can take.
Your you can check if a particular connection is open via this mysql_ping(), i.e
$conn=mysql_connect(...);
if(mysql_ping($conn)){...};
so you can use this method to decide which database to choose.
For codeigniter, one approach (which is a rather bad one I would say, but an approach none the less), is to mess with the system files. In DB_Driver, in this portion of the code:
$this->conn_id = ($this->pconnect == FALSE) ? $this->db_connect() : $this->db_pconnect();
if ( ! $this->conn_id)
{
log_message('error', 'Unable to connect to the database');
if ($this->db_debug)
{
$this->display_error('db_unable_to_connect');
}
return FALSE;
}
is where it tries to connect and checks if connection was successful, and if not gives the error.
I'm not sure how you do exception handling in CI, but basically you should handle an exception and connect to a different database.
Since I dont know exception handling, say I create a database_backup.php file the config folder hostname, username, password, and database variable. Then I would change the code to this
$this->conn_id = ($this->pconnect == FALSE) ? $this->db_connect() : $this->db_pconnect();
if ( ! $this->conn_id) //oops, first connection failed
{
//no problem, change the credentials of the database to our backup credentials
$ci=&get_instance();
$ci->load->config('database_backup');
$this->username=$ci->config->item('username');
$this->password=$ci->config->item('password');
$this->database=$ci->config->item('database');
$this->hostname=$ci->config->item('hostname');
//try to connect to database once more
$this->conn_id = ($this->pconnect == FALSE) ? $this->db_connect() : $this->db_pconnect();
// No connection resource STILL?nothing we can do now, throw an error
if ( ! $this->conn_id)
{
log_message('error', 'Unable to connect to the database');
if ($this->db_debug)
{
$this->display_error('db_unable_to_connect');
}
return FALSE;
}
}

Answer 2

take a look at system/database/drivers/mysql/mysql_driver.php
find the function function db_connect() [or function db_pconnect() depending upon which one you using]
there is the connection code:
return #mysql_connect($this->hostname, $this->username, $this->password, TRUE);
change the logic to suit your need.
by the way, prefere to use the PDO driver instead as by default, codeigniter uses mysql_* of whose depreciation process started.