Q: The DNS server configured via cloud-init on CentOS 7.x does not take effect, even though cloud-init runs successfully. Why?
A: This issue may occur if the virtual machine template has three DNS servers already configured in the /etc/resolv.conf file, which prevents the addition of any more. This is a common limitation in Linux distributions that use /etc/resolv.conf for DNS configuration. cloud-init attempts to add a new DNS server to the existing list of servers in resolv.conf rather than replacing them. According to the resolv.conf(5) manual, only three DNS servers are allowed in resolv.conf. If the virtual machine template already contains three DNS servers configured in the /etc/resolv.conf file, cloud-init will fail to add a new one. In this case, the /var/log/cloud-init.log will record ignoring nameserver {dns_server}: adding would exceed the maximum of '3' name servers (see resolv.conf(5)).
Q: The DNS configured via cloud-init for operating systems that use the eni network configuration tool (such as Debian OS) does not take effect, even though cloud-init runs successfully. Why?
A: This issue may occur because the virtual machine typically uses resolvconf.service to configure DNS when configuring network via the eni network configuration tool. Some operating systems may not have this service installed, leading to DNS configuration failures. To resolve this, ensure that the resolvconf.service is installed when creating the template and configured to autostart on boot.
Q: The static IP, router, and DNS configured via cloud-init for operating systems that use the Netplan network configuration tool (such as Kylin Desktop v10) does not take effect, even though cloud-init runs successfully. Why?
A: This issue may occur when the systemd-networkd service is not set to autostart on boot, as it is essential for the virtual machine's Netplan network configuration tool to manage the network. Although the cloud-init service has written the expected configuration to the Netplan directory, the network configuration may fail for the systemd-networkd service is not running. In this case, run the netplan apply command to start the systemd-networkd service and apply the relevant configuration. If the described cause is accurate, the network configuration should then be successfully restored. You can use the command systemctl enable systemd-networkd when creating the cloud-init template to set the service to autostart on boot.
Q: The static IP network configured via cloud-init for operating systems that use the Netplan network configuration tool (such as Ubuntu 18.04 system) does not take effect, even though cloud-init runs successfully. Why?
A: This issue may occur when multiple configuration files exist in the /etc/netplan directory, such as 01-network-manager-all.yaml and 50-cloud-init.yaml, which the system processes sequentially, causing potential conflicts to interfere with the application of network configuration.
For example, if the 01-network-manager-all.yaml file specifies the DHCP configuration for the virtual NIC ens4, it may override or interfere with the configuration for ens4 in the 50-cloud-init.yaml file. Additionally, if the 01-network-manager-all.yaml file contains configurations for NICs that do not exist, it may also lead to network configuration failures, preventing the configurations in the 50-cloud-init.yaml file from being applied.
To address this issue, it is recommended to back up the 01-network-manager-all.yaml file and remove it from the /etc/netplan directory, then recreate the cloud-init template for creating cloud-init virtual machines.
Q: The static IP address configured via cloud-init for operating systems that use the eni network configuration tool (such as Debian or Ubuntu 16.04) does not take effect, even though cloud-init runs successfully. Why?
A: This issue may occur when the /etc/network/interfaces file is incorrectly configured.
Since cloud-init writes the network configuration info to the /etc/network/interfaces.d/50-cloud-init.cfg file, if the /etc/network/interfaces file is not configured correctly, the configurations in the 50-cloud-init.cfg file will be rendered ineffective, as well as the static IP address.
Refer to the following requirements when configuring the /etc/network/interfaces file.
Include source statements
The /etc/network/interfaces file must include the following statements to ensure that configuration files in the /etc/network/interfaces.d/* directory can be successfully loaded:
source /etc/network/interfaces.d/*
Avoid conflicts
The /etc/network/interfaces file should not contain the same configurations as the NIC specified in the /etc/network/interfaces.d/50-cloud-init.cfg file to prevent potential configuration conflicts.
Here's an example of a /etc/network/interfaces file that meets the requirements, where only the loopback interface lo is configured:
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
source /etc/network/interfaces.d/*
# The loopback network interface
auto lo
iface lo inet loopbackIt is recommended to modify the configuration as described above to ensure that the network configurations in the 50-cloud-init.cfg file are correctly loaded and taking effect.