My Bitnami LAMP instance delays for 5-10 seconds almost every other request.

The issue you're experiencing with your Bitnami LAMP instance on AWS Lightsail could be related to several factors, even though your instance appears to have sufficient resources and low usage. Here are some potential reasons and solutions to consider:

1. CPU Credit Depletion: Lightsail instances use a burstable performance model. Even if your average CPU usage is low, periodic spikes could be depleting your CPU credits, causing performance to drop to baseline levels. This could explain the alternating fast and slow responses.

2. Resource-Intensive Background Processes: There might be background processes, updates, or periodic tasks consuming resources intermittently, causing the delays you're observing.

3. Database Query Optimization: If your application relies on a database, slow or unoptimized queries could cause periodic delays, especially if they're triggered by certain requests.

4. Application Code Issues: The problem might lie within your application code. Inefficient algorithms or resource management could lead to sporadic slow responses.

5. Network Latency: Although less likely given the pattern you described, network issues between your client and the Lightsail instance could contribute to intermittent delays.

To address these issues:

1. Monitor your instance: Use Lightsail's built-in monitoring tools to check CPU usage, burst capacity, and other metrics during both fast and slow response periods.

2. Optimize your application: Review and optimize your application code, focusing on database queries and resource management.

3. Check for background processes: Investigate any scheduled tasks or updates that might be running periodically.

4. Consider upgrading: If you consistently need more resources, you might benefit from upgrading to a larger Lightsail plan with higher baseline performance.

5. Application profiling: Use application performance monitoring tools to identify bottlenecks in your code or database queries.

6. Implement caching: Where appropriate, implement caching mechanisms to reduce load on your server and improve response times.

If the problem persists after trying these solutions, you may want to consider reaching out to AWS support for more detailed assistance with your specific instance and application setup.
Sources
My LightSail Bitnami LAMP is too slow and at times unresponsive | AWS re:Post
My LightSail Bitnami LAMP instance crashing | AWS re:Post
EC2 Server Late response issue | AWS re:Post