EC2 instance intermittently locking up (network OUT drops to zero)

Question

Hi,

We have been running a good sized t3 instance without major issues for years.  About a month ago we "upgraded" from centos7 to almalinux8 via cpanel script.  After a week we started getting daily issues with the instance locking up (at varying times, usually once a day), CPU and RAM initially increase (below max) then network OUT traffic drops to zero and stays there permanently unless the instance is rebooted.  We doubled the EC2 instance size and no change in behaviour.  cPanel has said there are no known issues with the upgrade script.

We have never touched the AWS network settings.  However:
```
Feb  5 06:05:00 {server} network[1139]: ERROR     : [/etc/sysconfig/network-scripts/ifup-eth] Device eth0 does not seem to be present, delaying initialization.
```

No network device is configured on the server, but presumably AWS takes care of this behind the scenes (otherwise it would never be visible online?).  It is configured in the network-scripts folder:
```
DEVICE="eth0"
BOOTPROTO="dhcp"
ONBOOT="yes"
TYPE="Ethernet"
USERCTL="yes"
PEERDNS="yes"
IPV6INIT="no"
PERSISTENT_DHCLIENT="1"
```

Its not clear if network issues are the cause or symptom.  Any pointers on possible causes would be gratefully received.  This has been going for more than 3 weeks and is causing us a huge headache

Many thanks in advance

Answer

I came across your issue regarding the EC2 instance experiencing network drops and system lock-ups following an upgrade from *CentOS 7* to *AlmaLinux 8*. It's a challenging situation, but there are a few steps you can take to potentially resolve this:

* **Network Interface Naming Convention**: The upgrade to *AlmaLinux 8* might have changed the naming convention for network interfaces from `eth0` to something more hardware-specific. Running `ip link` will show you the current names, which you can then update in your network configuration to match.
* **Network Management Compatibility**: *AlmaLinux 8* prefers using *NetworkManager*, a shift from the older network scripts method. Ensure that your system's network management aligns with NetworkManager's expectations, or adjust your scripts to be compatible.
* **Review Network Configuration Files**: The files in `/etc/sysconfig/network-scripts/` might still reference `eth0`, which could no longer exist. Update these files to accurately reflect the interface names shown by ip link.
* **Update Custom and Legacy Scripts**: Any scripts that were tailored for *CentOS 7* might not be fully compatible with *AlmaLinux 8*. Review and update these scripts to ensure they're in line with the new system's requirements.
* **Verify Interface Recognition**: Use `ls /sys/class/net/` to list recognized network interfaces. If `eth0` is missing, it indicates a need to adjust your configuration or check for driver issues.

These resources may help you:
1. https://unix.stackexchange.com/questions/134483/why-is-my-ethernet-interface-called-enp0s10-instead-of-eth0
2. https://wiki.crowncloud.net/?How_to_disable_NetworkManager_in_AlmaLinux_8#Installing+network-scripts

EC2 instance intermittently locking up (network OUT drops to zero)

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