Fix incorrect service name being set in the nginx template

[adrianmoisey]

This handles the case where multiple rules have identical paths, but differing types.
This should populate the $service_name variable with the correct service name.

What this PR does / why we need it:

Fixes: #10210

At the moment if multiple rules contain the same path, sometimes the incorrect service name may be set in the $service_name variable

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• CVE Report (Scanner found CVE and adding report)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation only

Which issue/s this PR fixes

fixes #10210

How Has This Been Tested?

Test case added in PR.
Manual testing locally and checking the outputted nginx.conf file

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have added unit and/or e2e tests to cover my changes.
• All new and existing tests passed.

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[adrianmoisey]

I'm unsure if this is the best way to handle the type assertion.
It seems like we may get the correct type, or nothing at all (empty string I think).
Happy to change this if anyone has a suggestion.

[Gacko]

/triage accepted
/kind bug
/priority backlog
/cc @strongjz @tao12345666333

[Gacko]

/cherry-pick release-1.10

[k8s-infra-cherrypick-robot]

@Gacko: once the present PR merges, I will cherry-pick it on top of release-1.10 in a new PR and assign it to you.

In response to this:

/cherry-pick release-1.10

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[longwuyuan]

@adrianmoisey @Gacko Can you post the link proof from upstream K8S KEP, that clarifies, that identical host joined with identical path, is allowed to be a individual new rule, just because the pathType is different

[adrianmoisey]

Can you post the link proof from upstream K8S KEP, that clarifies, that identical host joined with identical path, is allowed to be a individual new rule, just because the pathType is different

Bullet point 4 from: https://github.com/kubernetes/enhancements/tree/master/keps/sig-network/758-ingress-api-group#path-matching-semantics

If there is more than one potential match:
Exact match is preferred to a Prefix match.
For multiple prefix matches, the longest Path p_i will be the matching path.
If an ImplementationSpecific match exists in the spec, then the preference depends on the implementation

Note: This PR isn't adding new paths/rules to nginx. It already does that.
This is just fixing the case where the incorrect service is set in $service_name in that location block, which causes metrics to be reported incorrectly (I'm unsure if other functionality relies on that variable)

[longwuyuan]

@adrianmoisey thanks for the link.

I am not a developer.
Do the words preferred and preference, in the context of the word match, imply that admission-webhook should allow 2 identical host+path rules, albeit with different pathTypes. Not being an expert, I think that itself is a mess, and a bigger mess than the current behavior of wrong-service-name.

I have just seen pattern of duplicates not being appropriate, for not-short-time now, simply because, regardless of admission-webook accepting duplicate combo of host+path or wrong-service-name in location, there is still a simple contention of which rule MATCHES the request. And it seems that the link you provided just explains how (at least some) the duplicates are evaluated for a match, to route the request.

These are my thoughts. Will wait to get educated on the intricacies. It means now we clearly support duplicates in the project.

[longwuyuan]

Also, from the point of view of benefit to mass of users, admission-webhook should not allow duplicates.

I do understand that temporary duplicates help in migration as well as permanent duplicates as variants of pathType though.

So its a question of having a messy feature that is a antipattern to ingress traffic or having such a feature and maintaining it but only a couple of users getting benefit from the feature.

[Gacko]

/ok-to-test

[Gacko]

/assign

[adrianmoisey]

I'm unsure if this is the best way to handle the type assertion.
It seems like we may get the correct type, or nothing at all (empty string I think).
Happy to change this if anyone has a suggestion.

I guess another option is to default to ImplementationSpecific , should this assertion fail (https://github.com/kubernetes/enhancements/tree/master/keps/sig-network/758-ingress-api-group#defaults)

[adrianmoisey]

Also, from the point of view of benefit to mass of users, admission-webhook should not allow duplicates.

I do understand that temporary duplicates help in migration as well as permanent duplicates as variants of pathType though.

So its a question of having a messy feature that is a antipattern to ingress traffic or having such a feature and maintaining it but only a couple of users getting benefit from the feature.

I'm not sure I understand why this is considered an anti-pattern.
We have a valid use case where / goes to one service, and /* goes to another service.

However, my PR is simply a bug fix, it's not really related to if a feature should or shouldn't exist.

[longwuyuan]

Hi @adrianmoisey ,
You are right. My comments are not directly related to the changes you propose in this PR.

However its the broader context that has become visible via this PR and hence my comments.