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PHP application logging with Amazon CloudWatch Logs and Monolog

by Joseph Fontes | on | in PHP | Permalink | Comments |  Share

Logging and information debugging can be approached from a multitude of different angles. Whether you use an application framework or coding from scratch it’s always comforting to have familiar components and tools across different projects. In our examples today, I am going to enable Amazon CloudWatch Logs logging with a PHP application. To accomplish this, I wanted to use an existing solution that is both already popular and well used, and that is standards compliant. For these reasons, we are going to use the open source log library, PHP Monolog (

PHP Monolog

For those who work with a new PHP application, framework, or service, one of the technology choices that appears more frequently across solutions is the use of Monolog for application logging. PHP Monolog is a standards-compliant PHP library that enables developers to send logs to various destination types including, databases, files, sockets, and different services. Although PHP Monolog predates the standards for PHP logging defined in PSR-3, it does implement the PSR-3 interface and standards. This makes Monolog compliant with the common interface for logging libraries. Using Monolog with CloudWatch Logs creates a PSR-3 compatible logging solution. Monolog is available for use with a number of different applications and frameworks such as Laravel, Symfony, CakePHP, and many others. Our example today is about using PHP Monolog to send information to CloudWatch Logs for the purpose of application logging and to build a structure and process that enables the use of our application data with CloudWatch alarms and notifications. This enables us to use logs from our application for cross-service actions such as with Amazon EC2 Auto Scaling decisions.

Amazon CloudWatch Logs

As a customer-driven organization, AWS is constantly building and releasing significant features and services requested by AWS customers and partners. One of those services that we highlight today is Amazon CloudWatch Logs. CloudWatch Logs enables you to store log file information from applications, operating systems and instances, AWS services, and various other sources. An earlier blog post highlighted the use of CloudWatch Logs with various programming examples.

Notice in the blog post that there is a PHP example that uses CloudWatch Logs to store an entry from an application. You can use this example and extend it as a standalone solution to provide logging to CloudWatch Logs from within your application. With our examples, we’ll enhance this opportunity by leveraging PHP Monolog.

Implementing Monolog

To begin using Monolog, we install the necessary libraries with the use of Composer ( The instructions below install the AWS SDK for PHP, PHP Monolog, and an add-on to Monolog that enables logging to CloudWatch Logs.

curl -sS | php
php composer.phar require aws/aws-sdk-php
php composer.phar require monolog/monolog
php composer.phar require maxbanton/cwh:^1.0

Alternatively, you can copy the following entry to the composer.json file and install it via the php composer.phar install command.

    "minimum-stability": "stable",
    "require": {
        "aws/aws-sdk-php": "^3.24",
        "aws/aws-php-sns-message-validator": "^1.1",
        "monolog/monolog": "^1.21",
        "maxbanton/cwh": "^1.0"

Local logging

Now that PHP Monolog is available for use, we can test the implementation. We start with an example of logging to a single file.

require "vendor/autoload.php";

use Monolog\Logger;
use Monolog\Formatter\LineFormatter;
use Monolog\Handler\StreamHandler;

$logFile = "testapp_local.log";

$logger = new Logger('TestApp01');
$formatter = new LineFormatter(null, null, false, true);
$infoHandler = new StreamHandler(__DIR__."/".$logFile, Logger::INFO);
$logger->info('Initial test of application logging.');

In the previous example, we start by requiring the composer libraries we installed earlier. The new Logger line sets the channel name as “TestApp01”. The next line creates a new LineFormatter that removes brackets around unused log items. The next line establishes the destination as the file name we identified, testapp_local.log, and associates that with the INFO log level. Next, we apply the format to our stream handler. Then we add the stream handler with the updated format to the handler list. Finally, a new message is logged with the log level of INFO. For information about log levels and different handlers, see the Monolog GitHub page and IETF RFC 5424 and PSR-3.

We can now view the contents of the log file to ensure functionality:

Syslog logging

Now that we are able to write a simple log entry to a local file, our next example uses the system Syslog to log events.

$logger = new Logger($appName);

$localFormatter = new LineFormatter(null, null, false, true);
$syslogFormatter = new LineFormatter("%channel%: %level_name%: %message% %context% %extra%",null,false,true);

$infoHandler = new StreamHandler(__DIR__."/".$logFile, Logger::INFO);

$warnHandler = new SyslogHandler($appName, $facility, Logger::WARNING);


$logger->info('Test of PHP application logging.');
$logger->warn('Test of the warning system logging.');

Here we can see that the format of the syslog messages has been changed with the value, $syslogFormatter. Because syslog provides a date/time with each log entry, we don’t need to include these values in our log text. The syslog facility is set to local0 with all WARNING messages sent to syslog with the INFO level messages and WARNING level messages logged to our local file. You can find additional information about Syslog facilities and log levels on the Syslog Wikipedia page.

Logging to CloudWatch Logs

Now that you’ve seen the basic use of Monolog, let’s send some logs over to CloudWatch Logs. We can use the Amazon Web Services CloudWatch Logs Handler for Monolog library to integrate Monolog with CloudWatch Logs. In our example, an authentication application produces log information.

use Aws\CloudWatchLogs\CloudWatchLogsClient;
use Maxbanton\Cwh\Handler\CloudWatch;
use Monolog\Logger;
use Monolog\Formatter\LineFormatter;
use Monolog\Handler\StreamHandler;
use Monolog\Handler\SyslogHandler;

$logFile = "testapp_local.log";
$appName = "TestApp01";
$facility = "local0";

// Get instance ID:
$url = "";
$instanceId = file_get_contents($url);

$cwClient = new CloudWatchLogsClient($awsCredentials);
// Log group name, will be created if none
$cwGroupName = 'php-app-logs';
// Log stream name, will be created if none
$cwStreamNameInstance = $instanceId;
// Instance ID as log stream name
$cwStreamNameApp = "TestAuthenticationApp";
// Days to keep logs, 14 by default
$cwRetentionDays = 90;

$cwHandlerInstanceNotice = new CloudWatch($cwClient, $cwGroupName, $cwStreamNameInstance, $cwRetentionDays, 10000, [ 'application' => 'php-testapp01' ],Logger::NOTICE);
$cwHandlerInstanceError = new CloudWatch($cwClient, $cwGroupName, $cwStreamNameInstance, $cwRetentionDays, 10000, [ 'application' => 'php-testapp01' ],Logger::ERROR);
$cwHandlerAppNotice = new CloudWatch($cwClient, $cwGroupName, $cwStreamNameApp, $cwRetentionDays, 10000, [ 'application' => 'php-testapp01' ],Logger::NOTICE);

$logger = new Logger('PHP Logging');

$formatter = new LineFormatter(null, null, false, true);
$syslogFormatter = new LineFormatter("%channel%: %level_name%: %message% %context% %extra%",null,false,true);
$infoHandler = new StreamHandler(__DIR__."/".$logFile, Logger::INFO);

$warnHandler = new SyslogHandler($appName, $facility, Logger::WARNING);



$logger->info('Initial test of application logging.');
$logger->warn('Test of the warning system logging.');
$logger->notice('Application Auth Event: ',[ 'function'=>'login-action','result'=>'login-success' ]);
$logger->notice('Application Auth Event: ',[ 'function'=>'login-action','result'=>'login-failure' ]);
$logger->error('Application ERROR: System Error');

In this example, application authentication events are passed as a PHP array and presented in CloudWatch Logs as JSON. The events with a result of login-success and login-failure are sent to both the log stream associated with the instance ID and to the log stream associated with the application name.


Using these different stream locations, we can create metrics and alarms at either a per-instance level or per-application level. Let’s assume that we want to create a metric for total number of users logged into our application over the past five minutes. Select your event group and then choose Create Metric Filter.

On the next page, we can create our filter and test in the same window. For the filter data, we use the JSON string from the log entry. Enter the following string to extract all the successful logins.

{ $.result = login-success }

Below, we can see the filter details. I updated the Filter Name to a value that’s easy to identify. The Metric Namespace now has a value associated with the application name and the metric name reflects the number of login-success values.


We could now create an alarm to send a notification or perform some action (such as an Amazon EC2 scaling decision), based on this information being received via CloudWatch Logs.

With these values, we would receive an alert each time there were more than 50 successful logins within a five-minute period.

Laravel logging

Monolog is used as the logging solution for a number of PHP applications and frameworks, including, the popular Laravel PHP framework. In this example, we’ll show the use of Monolog with CloudWatch Logs within Laravel. Our first step is to find out the current log settings for our Laravel application. If you open config/app.php within your application root, you see various log settings. By default, Laravel is set to log to a single log file using the baseline log level of debug.

Next, we add the AWS SDK for PHP as a service provider within Laravel using instructions and examples from here.

You also want to add the Monolog library for CloudWatch Logs to the composer.json file for inclusion in the application, as shown.

You now need to extend the current Laravel Monolog configuration with your custom configuration. You can find additional information about this step on the Laravel Error and Logging page. The following is an example of this addition to the bootstrap/app.php file.

use Maxbanton\Cwh\Handler\CloudWatch;

$app->configureMonologUsing( function($monolog) {

    $cwClient = App::make('aws')->createClient('CloudWatchLogs');
    $cwGroupName = env('AWS_CWL_GROUP', 'laravel-app-logs');
    $cwStreamNameApp = env('AWS_CWL_APP', 'laravel-app-name');
    $cwTagName = env('AWS_CWL_TAG_NAME', 'application');
    $cwTagValue = env('AWS_CWL_TAG_VALUE', 'laravel-testapp01');
    $cwRetentionDays = 90;
    $cwHandlerApp = new CloudWatch($cwClient, $cwGroupName, $cwStreamNameApp, $cwRetentionDays, 10000, [ $cwTagName => $cwTagValue ] );


For testing purposes, we add a logging call to a test route in routes/web.php.

Route::get('/test', function () {
    Log::warning('Clicking on test link!!!');
    return view('test');

When the test route is invoked, the logs now show in CloudWatch Logs.


In our examples, we’ve shown how to use PHP Monolog to log to a local file, syslog, and CloudWatch Logs. We have also demonstrated the integration of Monolog with CloudWatch Logs within a popular PHP application framework. Finally, we’ve shown how to create CloudWatch Logs metric filters and apply those to CloudWatch Alarms that make the data from the logs actionable with notifications, as well as scaling decisions. CloudWatch Logs provides a central logging capability for your PHP applications and, combined with Monolog, ensures the availability of the library for use within established projects and custom engagements.