Initialize contexts based on http hosts (MODX Revolution) - source: http://modxcms.com/forums/index.php/topic,63406.msg359673.html#msg359673

index.php

switch(strtolower(MODX_HTTP_HOST)) {
    case 'dns.tld1:80':
    case 'dns.tld1':
        $modx->initialize('ctx1');
    break;

    case 'dns.tld2:443':
    case 'dns.tld2:80':
    case 'dns.tld2':
        $modx->initialize('ctx2');
    break;
    
    default:
        $modx->initialize('web');
    break;
}