feat: add code samples for Connect Gateway API

[hodaaaaaaaaaa]

Description

Fixes b/369653672

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• I have followed Contributing Guidelines from CONTRIBUTING.MD
• Tests pass: go test -v ./.. (see Testing)
  Manually tested as the API call requires extensive setup shttps://cloud.google.com/kubernetes-engine/enterprise/multicluster-management/gateway/setup
• Code formatted: gofmt (see Formatting)
• Vetting pass: go vet (see Formatting)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
  connectgateway.googleapis.com, gkehub.googleapis.com
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

[gemini-code-assist]

Hello @hodaaaaaaaaaa, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

Summary of Changes

This pull request introduces a new sample for connecting to the Connect Gateway. It adds a new directory connectgateway with Go modules and a sample Go program (list_namespaces.go) that demonstrates how to list namespaces in a Kubernetes cluster using the GKE Connect Gateway. The pull request also updates the .github/CODEOWNERS file to include codeowners for the new connectgateway directory.

Highlights

• New Sample: Connect Gateway: A new sample directory connectgateway is added, showcasing how to connect to and interact with the GKE Connect Gateway using Go.
• Go Modules: The pull request includes go.mod and go.sum files for managing dependencies required by the new sample.
• List Namespaces Implementation: The list_namespaces.go file contains the implementation for listing Kubernetes namespaces using the GKE Connect Gateway.
• Codeowners Update: The .github/CODEOWNERS file is updated to include the appropriate codeowners for the new connectgateway directory.

Changelog

Click here to see the changelog

• .github/CODEOWNERS
  • Added /connectgateway/ with codeowners @GoogleCloudPlatform/go-samples-reviewers, @GoogleCloudPlatform/cloud-samples-reviewers, and @GoogleCloudPlatform/connect-gateway.
• connectgateway/go.mod
  • Added a new go.mod file for the connectgateway sample.
  • Specifies the module name as main.
  • Declares dependencies on cloud.google.com/go/gkeconnect, golang.org/x/oauth2, k8s.io/api, k8s.io/apimachinery, and k8s.io/client-go.
• connectgateway/go.sum
  • Added a new go.sum file for the connectgateway sample.
  • Lists the checksums of the dependencies specified in go.mod.
• connectgateway/list_namespaces.go
  • Added a new Go program to list Kubernetes namespaces using the GKE Connect Gateway.
  • Includes functions to get the Gateway URL, configure the Kubernetes client, and call the List Namespaces API.
  • Uses cloud.google.com/go/gkeconnect/gateway/apiv1 to interact with the GKE Connect Gateway.
  • Uses k8s.io/client-go/kubernetes to interact with the Kubernetes API.
  • Accepts projectID, membershipID, membershipLocation, and serviceAccountKeyPath as command-line arguments.
• go.mod
  • Added cloud.google.com/go/gkeconnect v0.12.1 as a dependency.
  • Added k8s.io/apimachinery v0.32.4 and k8s.io/client-go v0.32.4 as dependencies.
  • Added indirect dependencies related to kubernetes and other google cloud packages.
• go.sum
  • Added checksums for cloud.google.com/go/gkeconnect v0.12.1.
  • Added checksums for k8s.io/apimachinery v0.32.4 and k8s.io/client-go v0.32.4.
  • Added checksums for indirect dependencies related to kubernetes and other google cloud packages.
• go.work
  • Added ./connectgateway to the use directive to include the new module in the workspace.
  • Upgraded go version to 1.25

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---

A gateway to connect,
Kubernetes namespaces inspect,
Go code takes flight,
Listing with all its might,
Cloud samples, quite correct.

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[gemini-code-assist]

Code Review

The pull request introduces a new sample for connecting to a gateway using golang. The code appears to be well-structured and follows common Go practices. However, there are a few areas that could be improved for clarity and robustness.

Summary of Findings

• Error Handling: The error handling in getGatewayURL could be improved by providing more context to the user about the specific failure.
• Argument Validation: The main function could benefit from more robust argument validation to ensure that the program is called with the correct number of arguments and that the arguments are valid.
• Dependency Versions: The go.mod file has a mix of specific versions and some older versions. It would be good to update these to the latest versions.

Merge Readiness

The pull request introduces a new sample and appears to be well-structured. However, there are a few areas that could be improved for clarity and robustness. I would recommend addressing the high severity issues before merging. I am unable to directly approve this pull request, and recommend that others review and approve this code before merging.

[glasnt]

Googlers: see internal bug for updates

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• connectgateway/get_namespace.go:17, tag connectgateway_get_namespace

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[telpirion]

Hi @hodaaaaaaaaaa ,

Thank you for contributing this code sample! Please address the comments and I will take another look.

[telpirion]

From my review, this looks very close to being ready. Thank you for addressing that first round of comments.

@glasnt -- please take another look when you get a chance.

[glasnt]

Configuration changes look ok, I'm not a go-language code review to check that content.

I would ask why the root go.mod/go.sum files need changing for this sample, but if that's okay, then disregard.

[hodaaaaaaaaaa]

Configuration changes look ok, I'm not a go-language code review to check that content.

I would ask why the root go.mod/go.sum files need changing for this sample, but if that's okay, then disregard.

@telpirion not updating the root go.mod/go.sum breaks the build since ./connectgateway is added to the workspace. Can you comment on whether this update is ok?

[hodaaaaaaaaaa]

Configuration changes look ok, I'm not a go-language code review to check that content.
I would ask why the root go.mod/go.sum files need changing for this sample, but if that's okay, then disregard.

@telpirion not updating the root go.mod/go.sum breaks the build since ./connectgateway is added to the workspace. Can you comment on whether this update is ok?

I downgraded the version to 1.23 and removed the parent dir changes. All checks are passing now.

No longer needed.