EC2 freezes at exactly one hour after reboot

Question

I am running a EC2 (**m6i.large**) with Jenkins/PHP/MySQL + some basic services. It was running on **18.x Ubuntu** fine and I upgraded it to 20.x and then 22.x yesterday. Since then the EC2 freezes (unable to SSH) and getting the error "instance reachability check failed" in AWS Console.

These are the last few logs from `dmesg`.

````
[    5.988941] audit: type=1400 audit(1713911132.732:28): apparmor="STATUS" operation="profile_load" profile="unconfined" name="snap.firefox.hook.configure" pid=425 comm="apparmor_parser"
[    5.993150] audit: type=1400 audit(1713911132.736:29): apparmor="STATUS" operation="profile_load" profile="unconfined" name="snap.firefox.hook.disconnect-plug-host-hunspell" pid=428 comm="apparmor_parser"
[    6.002181] audit: type=1400 audit(1713911132.744:30): apparmor="STATUS" operation="profile_load" profile="unconfined" name="snap.firefox.hook.post-refresh" pid=429 comm="apparmor_parser"
[    6.008875] parport_pc 00:03: reported by Plug and Play ACPI
[    6.235431] ppdev: user-space parallel port driver
[    9.785646] bridge: filtering via arp/ip/ip6tables is no longer available by default. Update your scripts to load br_netfilter if you need this.
[    9.787920] Bridge firewalling registered
[    9.900718] loop8: detected capacity change from 0 to 8
[    9.984377] Initializing XFRM netlink socket
````

No error logs in `/var/log/*.log` before freeze.

`htop` shows normal or near zero CPU and memory usage before the freeze. No CPU spikes in the Monitoring tab in AWS Console.

I have disabled all the cron jobs.

This is the current OS version:

````
$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 22.04.4 LTS
Release:	22.04
Codename:	jammy
````

I have tried stopping all the services such as Jenkins/Docker/PHP/Nginx etc., but the server still freezes at 1 hour exactly (+ 3 to 6 seconds). I looked at `ps -eaf` and `systemctl list-units --type=service --state=running` and I don't see anything strange running there.

After I reboot, I am able to SSH and then it freezes again in 1 hour.

How do I go further investigate what's causing this?

Answer

it's worth checking:

* Insufficient disk space or inodes.
* File system errors: Run a file system check (fsck) during a reboot.
* Hardware issues: Consider changing the instance type temporarily to see if the problem is related to the specific virtual hardware of the m6i.large.

If it does not help, consider reaching out to AWS Support. They can provide insights from their end that are not visible to you, such as hardware failures or underlying network issues affecting your instance.

EC2 freezes at exactly one hour after reboot

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