Writing a logger for CakePHP isn’t very difficult. The work lies in implementing the CakeLogInterface , which requires that you implement a write method as follows:

<?php App::uses('BaseLog', 'Log/Engine'); class LogstashLog extends BaseLog { public function write($type, $message) { // write to some output. } } ?>

The above class can go into app/Lib/Log/Engine/LogstashLog.php . Once you’ve implemented the interface - and I recommend you do so by extending BaseLog - you may want to actually write the logs to some location. In our case, we want to ship these logs to Logstash , a log processing tool that can take logs and decompose them into useful information.

At the very base, log messages should have some context about the logs - specifically a timestamp. Rather than invent our own format, we’ll use ISO-8601, which Logstash can handle natively. We can represent this using the following bit of code:

<?php $format = 'Y-m-d\TH:i:s.uP'; echo date($format); // ISO-8601 compliant datetime ?>

Logstash also represents message as json in a specific format. Pre-formatting our log messages would allow Logstash to skip any regular expression parsing of our log messages. The following is the current format:

{ "@timestamp": "2012-12-18T01:01:46.092538Z", "@version": 1, }

All other fields are optional, and therefore our LogstashLog would look as follows:

<?php App::uses('BaseLog', 'Log/Engine'); class LogstashLog extends BaseLog { protected $format = 'Y-m-d\TH:i:s.uP'; public function write($type, $message) { $data = [ '@timestamp' => date($this->format), '@version' => 1, 'message' => $message, 'tags' => [$type], ]; // write to some output. } } ?>

We can use syslog to ship our logs. PHP defines the following three methods to interface with syslog , and I recommend reading up on them:

openlog : opens a connection to the system logger for a program

: opens a connection to the system logger for a program syslog : generates a log message that will be distributed by the system logger

: generates a log message that will be distributed by the system logger closelog : closes the descriptor being used to write to the system logger

Adding in syslog support will change our logger as follows:

<?php App::uses('BaseLog', 'Log/Engine'); class LogstashLog extends BaseLog { protected $format = 'Y-m-d\TH:i:s.uP'; protected $logLevels = [ 'emergency' => LOG_EMERG, 'alert' => LOG_ALERT, 'critical' => LOG_CRIT, 'error' => LOG_ERR, 'warning' => LOG_WARNING, 'notice' => LOG_NOTICE, 'info' => LOG_INFO, 'debug' => LOG_DEBUG, ]; public function write($type, $message) { $data = [ '@timestamp' => date($this->format), '@version' => 1, 'message' => $message, 'tags' => [$type], ]; if (!openlog('app', LOG_PID, LOG_USER)) { // Handle your logging error... return; } syslog($this->logLevels[$type], json_encode($data)); } } ?>

What if we wanted to include extra metadata? Well, we can modify our write method to allow $message to be an array as follows:

public function write($type, $message) { $message = is_array($message) ? $message : compact('message'); $data = array_merge(array( '@timestamp' => date($this->format), '@version' => 1, ), $message); if (isset($data['tags'])) { $data['tags'][] = $type; } else { $data['tags'] = [$type]; } if (!openlog('app', LOG_PID, LOG_USER)) { // Handle your logging error... return; } syslog($this->logLevels[$type], json_encode($data)); }

We never want to drop logs, so we’ll fallback to using FileLog as our parent class. When openlog returns false, we’ll simply call return parent::write($type, json_ecode($message)); . We can then later go back with a different log shipper and reprocess anything that couldn’t be shipped to Logstash.

Here is what our log engine will look like at the end of the day:

<?php App::uses('FileLog', 'Log'); class LogstashLog extends FileLog { protected $format = 'Y-m-d\TH:i:s.uP'; protected $logLevels = [ 'emergency' => LOG_EMERG, 'alert' => LOG_ALERT, 'critical' => LOG_CRIT, 'error' => LOG_ERR, 'warning' => LOG_WARNING, 'notice' => LOG_NOTICE, 'info' => LOG_INFO, 'debug' => LOG_DEBUG, ]; public function write($type, $message) { $message = is_array($message) ? $message : compact('message'); $data = array_merge(array( '@timestamp' => date($this->format), '@version' => 1, ), $message); if (isset($data['tags'])) { $data['tags'][] = $type; } else { $data['tags'] = [$type]; } if (!openlog('app', LOG_PID, LOG_USER)) { return parent::write($type, json_ecode($data)); } return syslog($this->logLevels[$type], json_encode($data)); } } ?>

We can now configure our custom logging engine the same way we would any other logging engine:

<?php // in our app/Config/bootstrap.php App::uses('CakeLog', 'Log'); CakeLog::config('debug', [ 'engine' => 'Logstash', 'types' => ['notice', 'info', 'debug'], 'file' => 'debug', ]); CakeLog::config('error', [ 'engine' => 'Logstash', 'types' => ['warning', 'error', 'critical', 'alert', 'emergency'], 'file' => 'error', ]); ?>

You’ll notice that we included some extra configuration information. This is primarily used for routing messages - we could in theory create a Null engine and use that for debug messages - though we also specify a file so that the parent FileLog class is properly configured.

Creating custom logging engines is quite simple with CakePHP, and it would be easy to extend this system to have log handlers and formatters.