Frequent Out of Memory issue

Based on what you have described, it sounds like the typical symptoms of an Out of Memory (OOM) Kill error. In these situations, your system runs out of memory and kills off lower-prioritized processes in order to maintain system stability. From the outside, this can appear like random slow downs or crashes while applications close in order to process higher influxes of inbound/outbound website requests. In regards to web servers, increases of inbound/outbound web requests does increase your overall resource needs, so instances of heavy traffic can result in the performance issues you've described.

It's also possible that CPU usage has reached past the allotted CPU usage that your plan has and have caused your Linode to freeze. Without the information about your plan and stats about your usage, it's hard to say where the issue could be stemming from. For example, if your Linode plan is 2GB which has 1 CPU core, its maximum CPU usage is 80% for a Shared plan—so essentially which has been running at almost 100% capacity.

You'll want to consider either continually monitor your CPU usage. The most common method of monitoring your Linode's performance is by using the top command. You can also configure email alerts, so when your CPU usage you'll receive notifications of when your CPU plan starts nearing its' allowed limit.

Generally, as system needs grow, the most direct solution to running out of resources is to upgrade to a larger plan with more resources. That said, you can also take steps to optimize your setup so as to better use the already available resources. For more information about OOM and how to optimize your website, be sure to check out the following Community posts:

• OOM issues - Apache and MySQL (18498) | Linode Questions
• Low memory error (22527) | Linode Questions