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When running PHP CLI commands inside a Docker container, it can be a challenge to manage error reporting and exception handling. One common scenario involves using New Relic’s daemon to track exception traces for your PHP applications. Unfortunately, New Relic only sends these exception traces after a 1-minute interval. This poses a significant problem: if your PHP process crashes due to an exception, the entire Docker container is killed immediately, and the error traces are never sent.

In this article, we explore a simple solution to keep your Docker container alive for a brief period after a PHP process crash. By employing a wrapper script, you can ensure that your container remains active long enough for New Relic to send those crucial exception traces.

Why Your Docker Container Gets Killed Immediately

The default behavior of Docker is to stop any running container once the main process inside it terminates. In PHP CLI applications, if an uncaught exception occurs, the PHP interpreter exits, and thus the Docker container follows. This behavior limits your ability to gather diagnostic information, particularly from monitoring tools like New Relic.

Solution: Using a Wrapper Script

To keep the Docker container alive for an additional minute after the PHP script encounters an exception, you can create a simple bash wrapper script. This script will monitor the PHP script's exit status and will hold the container open for a specified duration after any crash. Here's how you can implement this solution:

Step 1: Create the Wrapper Script

Create a file named run_php_with_new_relic.sh and include the following content:

#!/bin/bash php /path/to/your/script.php EXIT_CODE=$? sleep 60 # Keep the container alive for 60 seconds if there’s an error echo "Exit code: $EXIT_CODE" # Optional logging exit $EXIT_CODE 

Make sure to replace /path/to/your/script.php with the actual path to your PHP CLI script.

Step 2: Update Dockerfile

Modify your Dockerfile to utilize this wrapper script instead of executing the PHP application directly. Here’s an example:

FROM php:7.4-cli # Install New Relic daemon (replace with your actual installation steps) RUN apt-get update && apt-get install -y newrelic-daemon COPY run_php_with_new_relic.sh /usr/local/bin/run_php_with_new_relic.sh RUN chmod +x /usr/local/bin/run_php_with_new_relic.sh CMD ["/usr/local/bin/run_php_with_new_relic.sh"] 

Step 3: Build and Run Your Docker Container

Rebuild your Docker image and run your container as you normally would:

docker build -t my-php-app . docker run --rm my-php-app 

Explanation of the Wrapper Script

• The wrapper script executes the PHP CLI command and captures its exit code.
• If the PHP script exits due to an exception, the script pauses for 60 seconds before exiting, providing New Relic enough time to send the exception traces.
• You can adjust the sleep duration as needed, but ensure it's aligned with New Relic’s reporting interval for optimal effect.

Debugging and Logging

If you wish to capture the logs or any debugging information during the sleep duration, you can enhance the script to output additional details or redirect output to a log file:

#!/bin/bash php /path/to/your/script.php > /var/log/php-cli.log 2>&1 EXIT_CODE=$? sleep 60 echo "Exit code: $EXIT_CODE, captured logs above." exit $EXIT_CODE 

Alternative Approaches

If a wrapper is not suitable for your use case, consider keeping a lightweight health checker or supervisor process that ensures your application’s health and can trigger retries or error notifications to New Relic.

Frequently Asked Questions

Will this approach work with all versions of PHP?

Yes, as long as you follow the general structure of running the PHP CLI command in a wrapper script, it should work across various PHP versions.

Can I use other monitoring tools?

Absolutely! This approach is generic and should apply to any monitoring tool where you need to allow some processing time after a failure.

Is there a performance impact?

Generally, the performance overhead is negligible since Docker containers are designed to restart quickly. However, keep an eye on resource consumption during the sleep phase.

By applying this simple wrapper strategy, you can ensure that your Docker containers remain operational long enough for New Relic to capture essential metrics post-exception, facilitating better debugging and monitoring of your PHP applications.