As explained in the storage documentation, the filesystem on AWS Lambda is:

  • read-only, except for /tmp
  • not shared between lambda instances
  • not persistent

Because of that, logs should not be stored on disk.


The simplest solution is to push logs to AWS CloudWatch, AWS' service for logs.

PHP errors and warnings

By default, all PHP errors, warnings and notices emitted by PHP will be forwarded into CloudWatch.

That means that you don't have to configure anything to log errors, warnings or uncaught exceptions.

Writing logs

Your application can write logs to CloudWatch:

For example with Monolog (opens in a new tab):

$log = new Monolog\Logger('name');
$log->pushHandler(new StreamHandler('php://stderr', Logger::WARNING));
$log->warning('This is a warning!');

For simple needs, you can replace Monolog with Bref's logger (opens in a new tab), a PSR-3 logger designed for AWS Lambda:

$log = new \Bref\Logger\StderrLogger();
$log->warning('This is a warning!');

Reading logs

To read logs, either open the CloudWatch console (opens in a new tab) or the Bref Dashboard (opens in a new tab).

You can also use serverless logs to view them in the CLI:

serverless logs -f <function-name>
# Tail logs:
serverless logs -f <function-name> --tail