Heavy CPU usage during peak and port 25 connection timeout

[p44]

Can heavy CPU usage during peak load times cause problems with email reception, to the point where emails are “not handled” because port 25 is unreachable from outside the network, bringing to “25: Connection timed out” and to Undelivered Mail Returned to Sender.

I'm asking this question because I've had a similar problem and I'd like to know how to mitigate it.

I've already limited maximum CPU usage to 80% of every single app hosted on Cloudron, but I'd like to understand how the overall load is being managed, to the point where 25 port stops responding.

No any log on Cloudron (Server, Mail) about ”not handled” email.

Edit: allocated Ram show that every app and service has enough Ram. My question also is: there is a way to assign maximum CPU usage to each service, to “keep alive” essential one?

Edit2: Peak was caused from an high number of web pages served and a lot of incoming email received in very short time, like a time frame of 10-15 minutes.

Thanks a lot

[james]

Hello @p44

I would assume this is not only a CPU/RAM issue but also an IOPS issue.
A very high system load can also occur without the CPU and RAM being used too much.
In this case it is almost always the IOPS. So the system storage can't keep up.
Depending on your server setup and provider this might be worth looking into if your server is using HDD, SSD, NVMe drives or a shared storage from the provider.
We had multiple reports of vServers showing this load / IOPS behaviour when there were underlying issues with the whole provider node.
One time it was a netcup node failing RAID system that caused all vServers on that node to have massive IOPS and load issues.
Which was also first denied by the first level support and only after providing detailed performance measurements they acknowledged that something must be wrong with their storage raid.

Port 25 not being inaccessible could also hint towards the mail service crashing or running out of memory.
Please check your mail service in Cloudron if you might need to increase the RAM and also check the logs of the mail service for crash reports.

[p44]

@james Thanks a lot, I didn’t have any crash of Mail service and also RAM is ok. I’ll take a proper look to IOPS. Thanks for your advices.