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How to fix apache high CPU usage on Ubuntu

Posted May 14, 2020 4.6k views
Apache

In the past, I used to managed a WordPress site on DigitalOcean droplet (One-click app) with 2 vCore, 4GB of memory, Ubuntu 16.04, Apache 2.4.18, and mysql community version 5.7.29.

Then the website was transferred to a droplet with 2 vCore, 4GB of memory, Ubuntu 18.04, Apache 2.4.29, and mysql community version 8.0.20.

Instantly after went live on the new droplet apache (“apache2 -k start” on htop) started to spike CPU to 30 and 40% and down to 0 to 3% and then after a few moments up again, and down again.

This is how the average graphs looks like (more or less): ||__||___|
the old server, it used to look like this —————–.

Both were one-click WordPress servers from DigitalOcean with default settings. Also, in the old server, the CPU usage with the same and sometimes even more load was always a flat line of 3 to 6%.

  1. Why is this problem happening?
  2. How to troubleshoot the problem?
  3. How to fix the problem?
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mhweb
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mhweb
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1 answer
alexdo May 15, 2020

Hello, @mhweb

What you can do is to monitor the droplet’s performance and check from where the CPU usage is coming from. Apache might be consuming more resources if the traffic to your sites is bigger as well.

The thing is the issue might not be related with your website itself and you might experiencing the speed issues because your server is running low on memory. That is why it’s important to make sure that everything is operating normally.

You can also examine the logs for any killed processes as this will help you to see if the server is killing processes in order to remain stable. You can check this by looking at the /var/log/messages and search for kill, e.g

grep -i kill /var/log/messages

You can also check for out of memory (The OOM Killer) references in the log to see if the system is critically low on memory. This usually indicates that you need to upgrade if there are a lot of references.

grep -i oom /var/log/messages

You can exacute top or htop via ssh to see what process is taking the most CPU or memory. Both tools are really handy when it comes to monitor the server’s performance. I would like to mention that top comes installed by default and you might need to install htop.

For Ubuntu:

`sudo apt-get install htop

Top provides a simple, real-time table of your processes, with the largest consumers on top. Running htop, we can see that it has a similar output, but is colorized, and is more interactive:

There is a really useful tutorial you can check on how to use top, htop, netstat, du and other tools to Monitor Server Resources:

https://www.digitalocean.com/community/tutorials/how-to-use-top-netstat-du-other-tools-to-monitor-server-resources

You can also use sar to check what’s going on your droplet. With sar, you can monitor performance of various Linux subsystems (CPU, Memory, I/O..) in real time.

You can use it like this:

To check the memory usage (Free and Used ):

sar -r

To check the cpu usage:

sar -u

You can also check this tutorial for monitoring the CPU usage on your droplet:

https://www.digitalocean.com/community/tutorials/how-to-monitor-cpu-use-on-digitalocean-droplets

You can also track the performance with the Droplet Graphs which are available in your control panel. You can find more information here:

https://www.digitalocean.com/docs/droplets/how-to/graphs/

Another thing that you could try using is this script here which summarizes your access logs. It would summarize your access log and give you the following information:

  • Top 20 POST requests
  • Top 20 GET requests
  • Top 20 IP logs and their geo-location

Another thing that could be causing the high CPU load is a cron job or any other scheduled task. I would recommend checking your crontab and reviewing your cron jobs. To do that you can run this command here:

  • crontab -l

Hope that this helps!

Regards,
Alex

How To Use Top, Netstat, Du, & Other Tools to Monitor Server Resources
by Justin Ellingwood
Monitoring a server's resources is an important task for every administrator. There are many command line tools made for this purpose. This guide will cover some of the more popular utilities for monitoring your VPS.
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  • mhweb May 15, 2020

    Thanks, I will check this out, but are you certain of the information? For example, the log/messages is a deprecated option.

    Oh, and I know about the problem because I used htop and syslog file.

    Reply Report
    • alexdo May 16, 2020

      Hey, @mhweb

      The /var/log/messages file doesn’t exist anymore on some distributions, that is correct most notably Ubuntu. Instead, the /var/log/syslog file is used. However you can still check if there are references in the log.

      Also you know that apache is causing the CPU spikes, but you still need to check if this is caused from general website traffic or the Apache configuration needs a tweak. For example the Apache workers can be exceeded and this can cause a CPU and memory spikes. You need to check the apache error_log and see if there are any logged errorss about this.

      You can also consider changing the Apache MPM in case you’re using prefork. You can check this using this command:

      apachectl -V | grep MPM

      Using MPM Event or Worker is considered a better option. I will recommend using Event.

      Worker

      Unlike Prefork, each child process under Worker can have multiple threads. As such, Worker can handle more requests with fewer resources than Prefork. Worker generally is recommended for high-traffic servers running Apache versions prior to 2.4. However, Worker is incompatible with non-thread safe libraries. If you need to run something that isn’t thread safe, you will need to stick with Prefork.

      Event

      Each process under Event also can contain multiple threads but, unlike Worker, each is capable of more than one task. Apache has the lowest resource requirements when used with the Event MPM. Event, though, is supported only on servers running Apache 2.4. Under Apache 2.2, Event is considered experimental and is incompatible with some modules on older versions of Apache. Nevertheless, on high-traffic Apache 2.2 servers where Apache has experienced issues with memory, upgrading Apache to take advantage of the Event MPM can yield significant results.

      Hope this helps!

      Regards,
      Alex

      Reply Report
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