Hostnames of ECSs created based on some types of images have the suffix .novalocal, whereas others do not.
For example, the hostname is set to abc during ECS creation. Table 1 lists the hostnames (obtained by running the hostname command) of ECSs created using different images and those displayed after the ECSs are restarted.
This is a normal phenomenon.
The static hostname of a Linux ECS is user defined and injected using Cloud-Init during the ECS creation. According to the test results, Cloud-Init adapts to OSs differently. As a result, hostnames of some ECSs have suffix .novalocal, whereas others do not.
If you do not need suffix .novalocal in obtained hostnames, change the hostnames. For details, see How Can a Changed Static Hostname Take Effect Permanently?