Function for_each_instance_endpoint 

pub async fn for_each_instance_endpoint<F, Fut>(
    client: &Client,
    instance_refs: &[InstanceReference],
    with_rndc_key: bool,
    port_name: &str,
    operation: F,
) -> Result<(Option<String>, usize)>
where
    F: Fn(String, String, Option<RndcKeyData>) -> Fut,
    Fut: Future<Output = Result<()>>,

Execute an operation on all endpoints for a list of instance references.

This is the event-driven instance-based approach that operates on instances discovered via spec.bind9InstancesFrom selectors.

Arguments

• client - Kubernetes API client
• instance_refs - List of instance references to process
• with_rndc_key - Whether to load and pass RNDC keys for each instance
• port_name - Port name to use for endpoints (e.g., “rndc-api”, “dns-tcp”)
• operation - Async closure to execute for each endpoint

Returns

• Ok((first_endpoint, total_endpoints)) - First endpoint found and total count

Errors

Returns an error if all operations fail or if critical API calls fail.