[8.19] (backport #9612) Add /readiness and /liveness when enrolling with the container

[mergify]

What does this PR do?

Starts the monitoring endpoint when Elastic Agent is running as a container and has enrollment enabled. This allows the healthchecks in Kubernetes to succeed even when it is enrolling into Fleet. If enrollment to Fleet takes longer than the k8s healthchecks then it can result in the pod not being reported as healthy, which can cause it to be killed and then it never enrolls.

This also adds a simple /readiness endpoint that provides a different between ready and alive. There is a difference, and this provides the difference between the two.

Why is it important?

This ensures that healthchecks do not prevent enrollment from actually working. Enrollment will still fail and the container will restart, giving the same behavior.

Checklist

• I have read and understood the pull request guidelines of this project.
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool
• [ ] I have added an integration test or an E2E test

Disruptive User Impact

None

How to test this PR locally

$ docker run -it --rm -p 5066:5066 -e FLEET_ENROLL=1 -e FLEET_URL=https://invalid-url:443 -e FLEET_ENROLLMENT_TOKEN=invalid-token ${build_image}
$ curl -v http://localhost:5066/readiness
$ curl -v http://localhost:5066/liveness

Related issues

• Closes Liveness endpoint is not present when the container is enrolling #9611

---

This is an automatic backport of pull request #9612 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of c028f68 has failed:

On branch mergify/bp/8.19/pr-9612
Your branch is up to date with 'origin/8.19'.

You are currently cherry-picking commit c028f68fa.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	new file:   changelog/fragments/1756325090-Fix-missing-liveness-healthcheck-during-container-enrollment.yaml
	modified:   internal/pkg/agent/application/monitoring/liveness.go
	modified:   internal/pkg/agent/application/monitoring/liveness_test.go
	modified:   internal/pkg/agent/application/monitoring/process.go
	new file:   internal/pkg/agent/application/monitoring/readiness.go
	new file:   internal/pkg/agent/application/monitoring/readiness_test.go
	modified:   internal/pkg/agent/application/monitoring/server.go
	modified:   internal/pkg/agent/application/monitoring/v1_monitor.go
	modified:   internal/pkg/agent/cmd/run.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   internal/pkg/agent/application/monitoring/server_test.go
	both modified:   internal/pkg/agent/cmd/container.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)

[elasticmachine]

💔 Build Failed

• Buildkite Build
• Commit: d6b769e

Failed CI Steps

• check-ci
• Unit tests - Ubuntu 22.04
• Unit tests - Ubuntu 22.04
• Unit tests - Ubuntu 22.04 with requirefips build tag
• Unit tests - Ubuntu 22.04 with requirefips build tag
• Unit tests - fips140=only Ubuntu 22.04
• Unit tests - fips140=only Ubuntu 22.04
• Unit tests - Ubuntu 22.04 ARM64
• Unit tests - Ubuntu 22.04 ARM64
• Unit tests - Windows 2022
• Unit tests - Windows 2022
• Unit tests - Windows 2016
• Unit tests - Windows 2016
• Unit tests - macOS 15 ARM
• Unit tests - macOS 15 ARM
• Unit tests - Windows 10
• Unit tests - Windows 10
• Unit tests - Windows 11
• Unit tests - Windows 11
• :junit: Junit annotate
• Merge coverage reports
• :sonarqube: Continuous Code Inspection
• Packaging: linux/amd64 rpm
• Packaging: linux/amd64 rpm
• Packaging: Ubuntu x86_64 FIPS
• Packaging: Ubuntu x86_64 FIPS
• Packaging: linux/arm64 tar.gz
• Packaging: linux/arm64 tar.gz
• Packaging: Ubuntu arm64 FIPS
• Packaging: Ubuntu arm64 FIPS
• Packaging: windows/amd64 zip
• Packaging: windows/amd64 zip
• Packaging: Containers linux/amd64
• Packaging: Containers linux/arm64
• Packaging: Containers linux/amd64 FIPS
• Packaging: Containers linux/arm64 FIPS

History

cc @blakerouse

[mergify]

This pull request has not been merged yet. Could you please review and merge it @blakerouse? 🙏