370 lines
13 KiB
Rust
370 lines
13 KiB
Rust
// Import necessary items (though for this example, few are needed beyond std)
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use std::fmt;
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// --- Error Handling ---
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// A simple error type for demonstration purposes. In a real app, use `thiserror` or `anyhow`.
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#[derive(Debug)]
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enum OrchestrationError {
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CommandFailed(String),
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KubeClientError(String),
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TopologySetupFailed(String),
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}
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impl fmt::Display for OrchestrationError {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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match self {
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OrchestrationError::CommandFailed(e) => write!(f, "Command execution failed: {}", e),
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OrchestrationError::KubeClientError(e) => write!(f, "Kubernetes client error: {}", e),
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OrchestrationError::TopologySetupFailed(e) => write!(f, "Topology setup failed: {}", e),
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}
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}
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}
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impl std::error::Error for OrchestrationError {}
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// Define a common Result type
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type Result<T> = std::result::Result<T, Box<dyn std::error::Error>>;
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// --- 1. Capability Specification (as Traits) ---
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/// Capability trait representing the ability to run Linux commands.
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/// This follows the "Parse, Don't Validate" idea implicitly - if you have an object
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/// implementing this, you know you *can* run commands, no need to check later.
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trait LinuxOperations {
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fn run_command(&self, command: &str) -> Result<String>;
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}
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/// A mock Kubernetes client trait for demonstration.
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trait KubeClient {
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fn apply_manifest(&self, manifest: &str) -> Result<()>;
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fn get_pods(&self, namespace: &str) -> Result<Vec<String>>;
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}
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/// Mock implementation of a KubeClient.
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struct MockKubeClient {
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cluster_name: String,
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}
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impl KubeClient for MockKubeClient {
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fn apply_manifest(&self, manifest: &str) -> Result<()> {
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println!(
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"[{}] Applying Kubernetes manifest:\n---\n{}\n---",
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self.cluster_name, manifest
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);
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// Simulate success or failure
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if manifest.contains("invalid") {
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Err(Box::new(OrchestrationError::KubeClientError(
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"Invalid manifest content".into(),
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)))
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} else {
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Ok(())
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}
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}
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fn get_pods(&self, namespace: &str) -> Result<Vec<String>> {
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println!(
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"[{}] Getting pods in namespace '{}'",
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self.cluster_name, namespace
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);
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Ok(vec![
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format!("pod-a-12345-{}-{}", namespace, self.cluster_name),
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format!("pod-b-67890-{}-{}", namespace, self.cluster_name),
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])
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}
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}
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/// Capability trait representing access to a Kubernetes cluster.
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/// This follows Rust Embedded WG's "Zero-Cost Abstractions" - the trait itself
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/// adds no runtime overhead, only compile-time structure.
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trait KubernetesCluster {
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// Provides access to a Kubernetes client instance.
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// Using `impl Trait` in return position for flexibility.
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fn get_kube_client(&self) -> Result<impl KubeClient>;
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}
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// --- 2. Topology Implementations ---
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// Topologies implement the capabilities they provide.
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/// Represents a basic Linux host.
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#[derive(Debug, Clone)]
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struct LinuxHostTopology {
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hostname: String,
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// In a real scenario: SSH connection details, etc.
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}
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impl LinuxHostTopology {
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fn new(hostname: &str) -> Self {
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println!("Initializing LinuxHostTopology for {}", hostname);
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Self {
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hostname: hostname.to_string(),
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}
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}
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}
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// LinuxHostTopology provides LinuxOperations capability.
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impl LinuxOperations for LinuxHostTopology {
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fn run_command(&self, command: &str) -> Result<String> {
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println!("[{}] Running command: '{}'", self.hostname, command);
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// Simulate command execution (e.g., via SSH)
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if command.starts_with("fail") {
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Err(Box::new(OrchestrationError::CommandFailed(format!(
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"Command '{}' failed",
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command
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))))
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} else {
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Ok(format!("Output of '{}' on {}", command, self.hostname))
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}
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}
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}
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/// Represents a K3D (Kubernetes in Docker) cluster running on a host.
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#[derive(Debug, Clone)]
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struct K3DTopology {
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cluster_name: String,
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host_os: String, // Example: might implicitly run commands on the underlying host
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// In a real scenario: Kubeconfig path, Docker client, etc.
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}
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impl K3DTopology {
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fn new(cluster_name: &str) -> Self {
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println!("Initializing K3DTopology for cluster {}", cluster_name);
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Self {
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cluster_name: cluster_name.to_string(),
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host_os: "Linux".to_string(), // Assume k3d runs on Linux for this example
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}
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}
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}
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// K3DTopology provides KubernetesCluster capability.
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impl KubernetesCluster for K3DTopology {
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fn get_kube_client(&self) -> Result<impl KubeClient> {
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println!("[{}] Creating mock Kubernetes client", self.cluster_name);
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// In a real scenario, this would initialize a client using kubeconfig etc.
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Ok(MockKubeClient {
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cluster_name: self.cluster_name.clone(),
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})
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}
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}
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// K3DTopology *also* provides LinuxOperations (e.g., for running commands inside nodes or on the host managing k3d).
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impl LinuxOperations for K3DTopology {
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fn run_command(&self, command: &str) -> Result<String> {
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println!(
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"[{} on {} host] Running command: '{}'",
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self.cluster_name, self.host_os, command
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);
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// Simulate command execution (maybe `docker exec` or similar)
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if command.starts_with("fail") {
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Err(Box::new(OrchestrationError::CommandFailed(format!(
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"Command '{}' failed within k3d context",
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command
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))))
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} else {
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Ok(format!(
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"Output of '{}' within k3d cluster {}",
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command, self.cluster_name
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))
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}
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}
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}
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// --- 3. Score Implementations ---
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// Scores require capabilities via trait bounds on their execution logic.
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/// Base trait for identifying scores. Could be empty or hold metadata.
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trait Score {
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fn name(&self) -> &'static str;
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// We don't put execute here, as its signature depends on required capabilities.
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}
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/// A score that runs a shell command on a Linux host.
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#[derive(Debug)]
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struct CommandScore {
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command: String,
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}
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impl Score for CommandScore {
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fn name(&self) -> &'static str {
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"CommandScore"
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}
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}
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impl CommandScore {
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fn new(command: &str) -> Self {
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Self {
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command: command.to_string(),
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}
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}
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/// Execute method is generic over T, but requires T implements LinuxOperations.
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/// This follows the "Scores as Polymorphic Functions" idea.
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fn execute<T: LinuxOperations + ?Sized>(&self, topology: &T) -> Result<()> {
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println!("Executing Score: {}", Score::name(self));
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let output = topology.run_command(&self.command)?;
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println!("Command Score Output: {}", output);
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Ok(())
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}
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}
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/// A score that applies a Kubernetes resource manifest.
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#[derive(Debug)]
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struct K8sResourceScore {
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manifest_path: String, // Path or content
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}
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impl Score for K8sResourceScore {
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fn name(&self) -> &'static str {
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"K8sResourceScore"
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}
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}
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impl K8sResourceScore {
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fn new(manifest_path: &str) -> Self {
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Self {
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manifest_path: manifest_path.to_string(),
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}
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}
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/// Execute method requires T implements KubernetesCluster.
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fn execute<T: KubernetesCluster + ?Sized>(&self, topology: &T) -> Result<()> {
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println!("Executing Score: {}", Score::name(self));
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let client = topology.get_kube_client()?;
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let manifest_content = format!(
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"apiVersion: v1\nkind: Pod\nmetadata:\n name: my-pod-from-{}",
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self.manifest_path
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); // Simulate reading file
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client.apply_manifest(&manifest_content)?;
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println!(
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"K8s Resource Score applied manifest: {}",
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self.manifest_path
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);
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Ok(())
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}
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}
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// --- 4. Maestro (The Orchestrator) ---
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// This version of Maestro uses a helper trait (`ScoreRunner`) to enable
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// storing heterogeneous scores while preserving compile-time checks.
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/// A helper trait to erase the specific capability requirements *after*
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/// the compiler has verified them, allowing storage in a Vec.
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/// The verification happens in the blanket impls below.
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trait ScoreRunner<T> {
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// T is the concrete Topology type
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fn run(&self, topology: &T) -> Result<()>;
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fn name(&self) -> &'static str;
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}
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// Blanket implementation: A CommandScore can be run on any Topology T
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// *if and only if* T implements LinuxOperations.
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// The compiler checks this bound when `add_score` is called.
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impl<T: LinuxOperations> ScoreRunner<T> for CommandScore {
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fn run(&self, topology: &T) -> Result<()> {
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self.execute(topology) // Call the capability-specific execute method
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}
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fn name(&self) -> &'static str {
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Score::name(self)
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}
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}
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// Blanket implementation: A K8sResourceScore can be run on any Topology T
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// *if and only if* T implements KubernetesCluster.
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impl<T: KubernetesCluster> ScoreRunner<T> for K8sResourceScore {
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fn run(&self, topology: &T) -> Result<()> {
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self.execute(topology) // Call the capability-specific execute method
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}
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fn name(&self) -> &'static str {
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Score::name(self)
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}
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}
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/// The Maestro orchestrator, strongly typed to a specific Topology `T`.
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struct Maestro<T> {
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topology: T,
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// Stores type-erased runners, but addition is type-safe.
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scores: Vec<Box<dyn ScoreRunner<T>>>,
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}
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impl<T> Maestro<T> {
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/// Creates a new Maestro instance bound to a specific topology.
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fn new(topology: T) -> Self {
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println!("Maestro initialized.");
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Maestro {
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topology,
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scores: Vec::new(),
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}
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}
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/// Adds a score to the Maestro.
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/// **Compile-time check happens here!**
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/// The `S: ScoreRunner<T>` bound ensures that the score `S` provides an
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/// implementation of `ScoreRunner` *for the specific topology type `T`*.
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/// The blanket impls above ensure this is only possible if `T` has the
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/// required capabilities for `S`.
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/// This directly follows the "Theoretical Example: The Compiler as an Ally".
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fn add_score<S>(&mut self, score: S)
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where
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S: Score + ScoreRunner<T> + 'static, // S must be runnable on *this* T
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{
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println!("Registering score: {}", Score::name(&score));
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self.scores.push(Box::new(score));
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}
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/// Runs all registered scores sequentially on the topology.
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fn run_all(&self) -> Vec<Result<()>> {
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println!("\n--- Running all scores ---");
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self.scores
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.iter()
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.map(|score_runner| {
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println!("---");
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let result = score_runner.run(&self.topology);
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match &result {
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Ok(_) => println!("Score '{}' completed successfully.", score_runner.name()),
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Err(e) => eprintln!("Score '{}' failed: {}", score_runner.name(), e),
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}
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result
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})
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.collect()
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}
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}
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// --- 5. Example Usage ---
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fn main() {
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println!("=== Scenario 1: Linux Host Topology ===");
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let linux_host = LinuxHostTopology::new("server1.example.com");
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let mut maestro_linux = Maestro::new(linux_host);
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// Add scores compatible with LinuxHostTopology (which has LinuxOperations)
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maestro_linux.add_score(CommandScore::new("uname -a"));
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maestro_linux.add_score(CommandScore::new("ls -l /tmp"));
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// *** Compile-time Error Example ***
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// Try adding a score that requires KubernetesCluster capability.
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// This line WILL NOT COMPILE because LinuxHostTopology does not implement KubernetesCluster,
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// therefore K8sResourceScore does not implement ScoreRunner<LinuxHostTopology>.
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// maestro_linux.add_score(K8sResourceScore::new("my-app.yaml"));
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// Uncomment the line above to see the compiler error! The error message will
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// likely point to the `ScoreRunner<LinuxHostTopology>` bound not being satisfied
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// for `K8sResourceScore`.
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let results_linux = maestro_linux.run_all();
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println!("\nLinux Host Results: {:?}", results_linux);
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println!("\n=== Scenario 2: K3D Topology ===");
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let k3d_cluster = K3DTopology::new("dev-cluster");
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let mut maestro_k3d = Maestro::new(k3d_cluster);
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// Add scores compatible with K3DTopology (which has LinuxOperations AND KubernetesCluster)
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maestro_k3d.add_score(CommandScore::new("pwd")); // Uses LinuxOperations
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maestro_k3d.add_score(K8sResourceScore::new("nginx-deployment.yaml")); // Uses KubernetesCluster
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maestro_k3d.add_score(K8sResourceScore::new("invalid-service.yaml")); // Test error case
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maestro_k3d.add_score(CommandScore::new("fail please")); // Test error case
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let results_k3d = maestro_k3d.run_all();
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println!("\nK3D Cluster Results: {:?}", results_k3d);
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println!("\n=== Compile-Time Safety Demonstrated ===");
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println!("(Check the commented-out line in the code for the compile error example)");
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}
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