add metrics env var requirement

[conceptualshark]

Description

Resolves #179

The "Configure the HTTP server" line is unhelpful/not descriptive. Update this to include mention of the actual env var required to configure metrics.

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support.
• This is already available but undocumented and should be released within a week.
• This on a specific schedule and the assignee will coordinate a release with the DevEx team. (apply hold label or convert to draft PR)
• This is part of a scheduled alpha or minor. (apply alpha or minor label)
• There is no urgency with this change and can be released at any time.

PR Checklist

• My changes are for an already released minor and are in /versioned_docs directory.
• My changes are for the next minor and are in /docs directory (aka /next/).

• My changes require an Engineering review, and I've assigned the Engineering DRI or delegate.
• My changes require a technical writer review, and I've assigned @camunda/tech-writers as a reviewer.

[github-actions]

👋 🤖 🤔 Hello! Did you make your changes in all the right places?

These files were changed only in docs/. You might want to duplicate these changes in versioned_docs/version-8.5/.

• docs/self-managed/zeebe-deployment/operations/metrics.md

You may have done this intentionally, but we wanted to point it out in case you didn't. You can read more about the versioning within our docs in our documentation guidelines.

[lenaschoenburg]

🔧 This configuration flag is enabling just one very specific type of metrics, the so called execution metrics. Even without this set, Zeebe exports many more metrics automatically by default. No extra configuration is required for this.

[conceptualshark]

• Do any changes need to be made to the config at all to export metrics?
• Are there other flags that should be added here (to enable metrics which aren't exported by default)? I'd like to make this section as complete as possible.

[lenaschoenburg]

Do any changes need to be made to the config at all to export metrics?

No, metrics are enabled by default.

Are there other flags that should be added here (to enable metrics which aren't exported by default)?

There are various flags that enable additional metrics. We leave them disabled by default because they have a performance impact and have a high cost to collect. For example:

• ZEEBE_BROKER_EXPERIMENTAL_ROCKSDB_ACCESSMETRICS=fine
• ZEEBE_BROKER_EXPERIMENTAL_FEATURES_ENABLEACTORMETRICS=true

I'd suggest to not mention them here, they are really only needed for debugging and performance tuning.

[conceptualshark]

@lenaschoenburg I've updated this to be more clear based on your comments. Assuming the execution metrics aren't experimental, is it worth calling out here? The original ask was specifically about how to find them, so there's definitely an interest in knowing, and they don't seem to be in any of our example YAML or I'd link there.

[lenaschoenburg]

Thanks for cleaning this up. Looks good to me 👍