fix: ScrapeClass TLSConfig nil pointer exception

[kakkoyun]

Signed-off-by: Kemal Akkoyun kakkoyun@gmail.com

Description

When only relabeling is configured in a ScrapeClass object, the TLSConfig field is nil. This causes a panic when the TLSConfig field is accessed in the ScrapeClass object.

I'm not sure about the business logic of the ScrapeClass TLSConfig field, but from pure Go perspective, it should fix the panic.

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x48 pc=0x1ad78e1]

goroutine 386 [running]:
github.com/prometheus-operator/prometheus-operator/pkg/prometheus.(*ConfigGenerator).MergeTLSConfigWithScrapeClass(0x20d7080?, 0xc00172b420, 0xc000fe6d08?)
        /home/runner/work/prometheus-operator/prometheus-operator/pkg/prometheus/promcfg.go:417 +0x81
github.com/prometheus-operator/prometheus-operator/pkg/prometheus.(*ConfigGenerator).generateServiceMonitorConfig(_, _, {{0xc000a7c250, 0x5}, 0x0, {0xc000a7c128, 0x8}, {0xc000a7c255, 0x5}, 0x0, ...}, ...)
        /home/runner/work/prometheus-operator/prometheus-operator/pkg/prometheus/promcfg.go:1370 +0xd3d
github.com/prometheus-operator/prometheus-operator/pkg/prometheus.(*ConfigGenerator).appendServiceMonitorConfigs(0xc000c5a6c0, {0x0, 0x0, 0x0}, 0xc0014ae420, 0x0, 0xc000b4d500, 0x1)
        /home/runner/work/prometheus-operator/prometheus-operator/pkg/prometheus/promcfg.go:2298 +0x3e5
github.com/prometheus-operator/prometheus-operator/pkg/prometheus.(*ConfigGenerator).GenerateServerConfiguration(0xc000c5a6c0, {0x27b2620, 0xc00098b540}, {0xc000e372fd, 0x3}, {0x0, 0x0}, _, _, {{0x0, ...}}, ...)
        /home/runner/work/prometheus-operator/prometheus-operator/pkg/prometheus/promcfg.go:672 +0x3f5
github.com/prometheus-operator/prometheus-operator/pkg/prometheus/server.(*Operator).createOrUpdateConfigurationSecret(0xc000173688, {0x27b2620, 0xc00098b540}, 0xc0010aa308, 0xc000c5a6c0, {0xc001adc830, 0x1, 0x1}, 0xc000b4d500)
        /home/runner/work/prometheus-operator/prometheus-operator/pkg/prometheus/server/operator.go:1152 +0xa68
github.com/prometheus-operator/prometheus-operator/pkg/prometheus/server.(*Operator).sync(0xc000173688, {0x27b2620, 0xc00098b540}, {0xc00148a060, 0xe})
        /home/runner/work/prometheus-operator/prometheus-operator/pkg/prometheus/server/operator.go:778 +0x8c5
github.com/prometheus-operator/prometheus-operator/pkg/prometheus/server.(*Operator).Sync(0xc000173688, {0x27b2620?, 0xc00098b540?}, {0xc00148a060, 0xe})
        /home/runner/work/prometheus-operator/prometheus-operator/pkg/prometheus/server/operator.go:725 +0x2c
github.com/prometheus-operator/prometheus-operator/pkg/operator.(*ResourceReconciler).processNextReconcileItem(0xc000066600, {0x27b2620, 0xc00098b540})
        /home/runner/work/prometheus-operator/prometheus-operator/pkg/operator/resource_reconciler.go:449 +0x231
github.com/prometheus-operator/prometheus-operator/pkg/operator.(*ResourceReconciler).Run.func1()
        /home/runner/work/prometheus-operator/prometheus-operator/pkg/operator/resource_reconciler.go:412 +0x3f
golang.org/x/sync/errgroup.(*Group).Go.func1()
        /home/runner/go/pkg/mod/golang.org/x/sync@v0.6.0/errgroup/errgroup.go:78 +0x56
created by golang.org/x/sync/errgroup.(*Group).Go in goroutine 497
        /home/runner/go/pkg/mod/golang.org/x/sync@v0.6.0/errgroup/errgroup.go:75 +0x96

Type of change

What type of changes does your code introduce to the Prometheus operator? Put an x in the box that apply.

• CHANGE (fix or feature that would cause existing functionality to not work as expected)
• FEATURE (non-breaking change which adds functionality)
• BUGFIX (non-breaking change which fixes an issue)
• ENHANCEMENT (non-breaking change which improves existing functionality)
• NONE (if none of the other choices apply. Example, tooling, build system, CI, docs, etc.)

Verification

Please check the Prometheus-Operator testing guidelines for recommendations about automated tests.

Example config to reproduce the issue:

apiVersion: monitoring.coreos.com/v1
kind: Prometheus
metadata:
  name: k8s
spec:
  scrapeClasses:
    - name: base-scrape-class
      default: true
      relabelings:
        - targetLabel: cluster
          replacement: my-awesome-cluster
      # tlsConfig: {} # This would work.

Changelog entry

Please put a one-line changelog entry below. This will be copied to the changelog file during the release process.

[BUGFIX] Fix ScrapeClass TLSConfig nil pointer panic when only relabeling is configured.

[xiu]

It looks good to me but I'd rather leave the approval to @nicolastakashi to check the logic.

Can we maybe add a test for this case in TestMergeTLSConfigWithScrapeClass?

[kakkoyun]

Can we maybe add a test for this case in TestMergeTLSConfigWithScrapeClass?

Good point. I'll ad it.

[simonpasquier]

I agree that tests would be good to have :)

[simonpasquier]

👍
@kakkoyun merge it at your will :)

[kakkoyun]

There's no merge button for me 😱 Could one of you please merge it?

[kakkoyun]

@simonpasquier Maybe I should have merged this to the release branch?

[simonpasquier]

@kakkoyun right it would be better to have the fix now rather than in a month. If you're motivated, you can cherry-pick the commit to the release-0.73 branch and push another PR.
cc @slashpai who's the current release shepherd :)

[slashpai]

@kakkoyun Since its already merged can you cherry-pick and create the PR to release branch?

[kakkoyun]

Thanks. I'll do it.