TRON-2333: Fix pod names ending in .--xxxx

[jfongatyelp]

There was an edge case where sanitized pod names ending up with .<6 characters> would then get truncated to something like .--<4 random chars> due to our truncation logic in get_sanitised_kubernetes_name.

However .--aaaa is not valid in a pod name as each section between .s must start with an alphanumeric character.

We saw errors such as the following when this case was hit:

{"reason":"FieldValueInvalid","message":"Invalid value: \"some-long-pod-name.--9b3a\": a lowercase RFC 1123 subdomain must consist of lower case alphanumeric characters, '-' or '.', and
must start and end with an alphanumeric character (e.g. 'example.com', regex used for validation is '[a-z0-9]([-a-z0-9]*[a-z0-9])?(\\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*')","field":"metadata.name"}

Solution

Before we try to add our truncation suffix, we simply strip any trailing . in our truncated name. This yields a pod name 1 character less than expected, but ensures pod name formats will continue to match previous expectations.

I also did not strip any further characters as . was the most important one that would cause validation to fail.

Verification

with the new test in place but using the old get_sanitised_kubernetes_name, the test fails as expected, with the non-RFC1123-compliant result:

E       AssertionError: assert 'hello--world.--cf28' == 'hello--world--cf28'
E
E         - hello--world--cf28
E         + hello--world.--cf28
E         ?             +