How I Solved Daily Crashes on My Low-RAM AWS Lightsail Server

Running a personal project on a budget-friendly server like AWS Lightsail is common, but it can come with stability challenges. One of my 512MB Lightsail instance, running the Grav CMS, began crashing like clockwork every single day. The monitoring graphs were misleading, showing only minor CPU spikes. This is the story of how I diagnosed the real problem and implemented a robust, low-cost solution.

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1. The Problem: Misleading CPU Spikes and Daily Crashes

The primary symptom was a daily server crash. At first glance, the AWS Lightsail monitoring console pointed to a CPU spike happening around the same time every day. However, the spike was only to about 25%, which isn’t nearly enough to take down a server.

This was the first major clue: the CPU spike was a symptom, not the cause. The real issue was that the process causing the CPU activity was also consuming all of the server’s limited 512MB of RAM, leading to a system crash from memory exhaustion (an Out-Of-Memory or “OOM” event).

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2. The Investigation: High-Level Troubleshooting Steps

With the hypothesis that RAM exhaustion from a scheduled task was the true cause, the investigation followed a logical path:

1. Analyze the Timing: The predictable, daily nature of the crash strongly suggested a cron job—a scheduled task run by the operating system.
2. Inspect Cron Job Directories: We investigated the system’s scheduling files, specifically /etc/crontab, /etc/cron.d/, and /etc/cron.daily/.
3. Identify Suspects: The initial suspects were a php script for cleaning sessions and logrotate for managing and compressing log files.
4. Confirm the Culprit: By checking the schedule of the php script (/etc/cron.d/php), we found it ran twice per hour. This did not match the single daily crash. The process of elimination pointed squarely at the scripts in /etc/cron.daily/, which run only once a day. The logrotate script, known for being memory-intensive when compressing large files, was identified as the most likely culprit.

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3. The Immediate Fix: Creating a Swap File Buffer

To prevent the server from crashing when logrotate ran, we needed to give it a memory buffer. Since upgrading the server instantly wasn’t the goal, creating a swap file was the perfect solution. A swap file is essentially a block of space on your server’s disk that the OS can use as “virtual RAM” when physical RAM runs out.

Adding a 1GB swap file is straightforward. The following commands create the file, set its permissions, activate it, and ensure it’s enabled every time the server reboots:

# Create a 1GB file named swapfile
sudo fallocate -l 1G /swapfile

# Set secure permissions so only the root user can access it
sudo chmod 600 /swapfile

# Format the file for use as swap space
sudo mkswap /swapfile

# Enable the swap file immediately
sudo swapon /swapfile

# Add it to the system's fstab file to make it permanent
echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

This provided the necessary safety net to handle the memory spike, instantly solving the daily crashes.

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4. The Long-Term Strategy: Cloudflare + Swap for Low-Cost Scaling 🚀

While the swap file ensures stability, it doesn’t solve for performance, as disk space is much slower than real RAM. To keep the server running smoothly on a cheap plan, the final step is to offload as much work as possible using a free service like Cloudflare.

Here’s how this powerful combination works:

• Cloudflare Caching: Cloudflare sits between your users and your Lightsail server. It automatically caches static content like images, CSS, and JavaScript at its data centers around the world. This means for most requests, your server doesn’t have to do any work at all, dramatically reducing its RAM and CPU load.
• Reduced Traffic Load: By absorbing traffic and blocking malicious bots, Cloudflare ensures that only legitimate requests reach your server.
• The Synergy: With Cloudflare handling the bulk of user traffic and the swap file providing a stability buffer for backend tasks like logrotate, your small server can handle significantly more than it could on its own.

This strategy allows you to continue using a low-cost Lightsail instance for much longer, getting the performance of a much larger setup without the extra cost.