feat(examples & workflows): Draft PR for adding prometheus-3 example

[SerbaC6]

No description provided.

[razvand]

Where is the Kraftfile for your example? Add the version number in the directory name.

Use your proper name in the commit message. Use Serban Ciumacencu, not SerbaC6.

Use a single commit. A commit is a unit of contribution. It can't reference a pull request, it can't be something thought of as draft. A commit is NOT a history of your struggles. A commit is an atomic contribution. Think of that when you create a commit. See instructions here and use the model of commits in the commit history.

[Copilot]

Pull request overview

Adds a Prometheus 3 example for Unikraft Cloud, including configuration, container/runtime definitions, documentation, and deployment workflows.

Changes:

• Adds Prometheus configuration and build files.
• Adds usage and customization documentation.
• Adds staging and stable workflows.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Review summary
prometheus-3/README.md	Nit (4 votes): Quickstart paths reference examples/prometheus instead of examples/prometheus-3.
prometheus-3/prometheus.yml	Critical (4 votes): Invalid indentation causes Prometheus configuration startup failures; reindent the complete file.
prometheus-3/Kraftfile	Critical (1 vote): Read-only erofs conflicts with TSDB/WAL writes under /prometheus; provide writable storage.
prometheus-3/Dockerfile	Moderate (3 votes): Alpine and Prometheus package versions are unpinned, so Prometheus 3 is not guaranteed.
.github/workflows/example-prometheus-3-staging.yaml	No final comments.
.github/workflows/example-prometheus-3-stable.yaml	No final comments.

Suppressed comments (6)

prometheus-3/Dockerfile:6

• The README says users can add rule files under rules/, and prometheus.yml loads rules/*.yml, but this image copies only prometheus.yml. Any rules added as documented are therefore absent from the rootfs and will not be loaded. Copy the rules into the image (with a matching in-image path) or remove/update that customization guidance.

COPY prometheus.yml /etc/prometheus/prometheus.yml

prometheus-3/README.md:148

• alpine:latest plus an unversioned apk add prometheus does not pin the Prometheus major version. A future Alpine update can install a different major even though the directory is named prometheus-3, so the note's compatibility and future-proofing claim is false. Pin the base/package versions or remove the version-specific claim.

* `FROM alpine:latest`: Use the latest Alpine Linux image as the base. 
  *(Note: The directory for this example is explicitly named `prometheus-3` because `alpine:latest` currently provides the 3.x series of Prometheus. This version pinning ensures the `prometheus.yml` configuration remains compatible and future-proofs the example against breaking changes in future major releases).*

prometheus-3/README.md:45

• The unikraft example explicitly configures port 443 as tls+http, but this kraft command omits the protocol. That changes the port mapping and can leave the HTTPS URL used in the following steps unable to reach Prometheus; keep the two commands equivalent.

kraft cloud deploy -p 443:9090 -M 2Gi .

prometheus-3/README.md:143

• Kraftfile is omitted from the customization list even though this new file controls the runtime/rootfs format and the Prometheus startup command. Comparable example READMEs document it alongside Dockerfile (for example, httpserver-nginx-vite-vanilla/README.md:121 and node24-karaoke/README.md:119), so readers are not told where to change these settings.

To customize the app, update the files in the repository, listed below:

* `prometheus.yml`: the Prometheus configuration file
* `Dockerfile`: the Docker-specified app filesystem

prometheus-3/README.md:82

• The sample network UUID contains g, which is not a hexadecimal UUID character, so this cannot be output from the CLI and makes the example misleading. Replace it with a valid UUID-shaped value.

- uuid:       a3ccf7b2-82e4-6693-14b3-2f53663g5eae

prometheus-3/prometheus.yml:56

• Even after the general indentation is corrected, labels is placed as a field of the my-app scrape config. Prometheus only accepts these labels inside the static_configs target group, beneath - targets; in the current structure configuration validation fails.

labels:
service: my-app
team: backend

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