Allow reducing the suffix length appended to instance templates name_prefix

[ralbertazzi]

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Description

Instance template resources provide a great name_prefix variable that allows using instance templates effectively on top of instance group managers. From what I can observe on the Google Cloud Console (which is validated by the equivalent code) a date-like suffix is appended to the name_prefix so that changes to instance templates in Terraform can result in the creation of different template resources with different names.

In our project we use a high number of instance groups (and corresponding templates) for which we'd like to set self-explanatory names, where ideally the instance group name is equal to the name prefix of its instance template. However, this is sometimes not possible because of the 37 characters length limitation required by the name_prefix. In this case, we have to come up with shorter names that feel like a hack and are not really self-explanatory.

While I see the reason for the suffix to be appended, I'm wondering if it would be possible to make it configurable such that we can append a shorter suffix, leaving more characters to the name_prefix. For instance I see that the suffix has some format 20230801144601276600000001 which contains the creation date up to seconds granularity (20230801144601) plus an extra suffix (276600000001). Since I don't expect in my case to create multiple instance templates with the same name_prefix within 1 second, I would be fine having just the first part of the suffix and dropping the second one. Another idea would be to use a short hash (4-6 characters) of the instance template parameters, which would leave me with almost 60 characters usable for the name_prefix.

New or Affected Resource(s)

• google_compute_region_instance_template
• google_compute_instance_template

b/312433567

[rileykarson]

We'd evaluate changing the default for all resources here as part of a major version. We don't want to add a knob, or change the format in a minor version.

[c2thorn]

Noting that we are intending to reduce the appended suffix in name_prefix globally, essentially changing the default value for many resources. This is a breaking change and is intended for the 6.0.0 major release.

[c2thorn]

Noting that we are intending to reduce the appended suffix in name_prefix globally, essentially changing the default value for many resources. This is a breaking change and is intended for the 6.0.0 major release.

We couldn't land on a new global UUID suffix that we felt wasn't prone to collisions. So we are keeping the current behavior for name_prefix's less than 38 characters, but allowing a new max of up to 54 characters with a shortened UUID suffix.

Current configs should not see the new behavior when upgrading to 6.0 unless changing the name_prefix to a length of 38 - 54 characters.

Resulting name for a name_prefix <= 37 characters:
name_prefix + YYYYmmddHHSSssss + 8 digit incremental counter
Resulting name for a name_prefix 38 - 54 characters:
name_prefix + YYmmdd + 3 digit incremental counter

[c2thorn]

closed with GoogleCloudPlatform/magic-modules#11448

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