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This document provides comprehensive documentation for a custom autoscaler API implemented in Rust using the Actix Web framework. The API is designed to manage scaling operations by exposing endpoints for health checks, retrieving metrics, triggering autoscaling events, managing configuration, and updating a Git repository. This Git update functionality is particularly useful for integrating dynamic scaling with GitOps workflows.

• Overview
• Architecture
• Endpoints
  • Health Check (GET /health)
  • Retrieve Metrics (GET /metrics)
  • Manual Autoscale Trigger (POST /autoscale)
  • Retrieve Configuration (GET /config)
  • Update Configuration (PUT /config)
  • Update Git Repository (POST /git/update)
• Setup and Installation
• Running the Server
• Testing and Debugging
• Authentication and Security Considerations
• Extending and Contributing
• License
• Full Source Code
• Conclusion

The Custom Autoscaler API is designed to:

• Monitor Metrics: Provide an API to retrieve system and application metrics.
• Trigger Autoscaling: Allow manual or automated scaling of resources such as a MariaDB cluster.
• Manage Configuration: Enable retrieval and updates to autoscaler configuration settings.
• Integrate with GitOps: Update configuration files in a Git repository by committing and pushing changes automatically.

The service is written in Rust and leverages several popular libraries including Actix Web for the HTTP server, Serde for JSON handling, Chrono for timestamp generation, and Git2 for interacting with Git repositories.

The application is divided into several key components:

• API Endpoints:
  Exposes RESTful endpoints for operations such as health checks, metrics retrieval, autoscaling actions, configuration management, and Git updates.

• Configuration Management:
  Uses shared application state with thread-safe access (via a mutex) to store and update autoscaler configuration.

• Git Integration Module:
  Uses the Git2 crate to modify files, stage changes, create commits, and push updates to a remote Git repository. This is useful for automatically reflecting scaling decisions in a GitOps workflow.

• Timestamping:
  Uses Chrono to append the current timestamp to all responses, which is useful for tracking when operations occurred.

• Description:
  Returns the current status of the API along with a timestamp.

• Response Example:

  {
    "status": "OK",
    "timestamp": "2025-04-08T12:34:56Z"
  }
  

Retrieve Metrics (GET /metrics) • Description: Retrieves current metrics such as CPU usage, memory usage, current replica counts, and target replica counts. (The example uses static values that you can replace with real data.) • Response Example:

{ "cpu_usage": "65%", "memory_usage": "1.2Gi", "current_replicas": 3, "target_replicas": 4, "metric_timestamp": "2025-04-08T12:33:00Z" }

Manual Autoscale Trigger (POST /autoscale) • Description: Triggers a manual scaling event for a specified resource by updating the replica count. • Request Body Example:

{ "resource": "MariaDBCluster", "namespace": "database", "target_replicas": 5 }

•	Response Example:

{ "status": "Scaling initiated", "resource": "MariaDBCluster", "namespace": "database", "new_replica_count": 5, "timestamp": "2025-04-08T12:35:10Z" }

Retrieve Configuration (GET /config) • Description: Retrieves the current autoscaler configuration. • Response Example:

{ "min_replicas": 2, "max_replicas": 10, "scale_up_threshold": 70, "scale_down_threshold": 30, "cool_down_period": 300 }

Update Configuration (PUT /config) • Description: Updates the autoscaler configuration parameters. • Request Body Example:

{ "min_replicas": 3, "max_replicas": 12, "scale_up_threshold": 75, "scale_down_threshold": 25, "cool_down_period": 600 }

•	Response Example:

{ "status": "Configuration updated", "updated_config": { "min_replicas": 3, "max_replicas": 12, "scale_up_threshold": 75, "scale_down_threshold": 25, "cool_down_period": 600 }, "timestamp": "2025-04-08T12:36:00Z" }

Update Git Repository (POST /git/update) • Description: Updates a specified file in the local Git repository, stages the changes, commits them, and pushes the commit to the remote. This is useful for updating configuration files (for example, YAML manifests) automatically as part of a GitOps workflow. • Request Body Example:

{ "file_path": "manifests/mariadb.yaml", "new_content": "replicas: 5", "commit_message": "Update replica count to 5" }

•	Workflow:
1.	File Update: Overwrites the specified file with new content.
2.	Staging: Adds the file to the Git index.
3.	Commit: Creates a commit with the provided commit message.
4.	Push: Pushes the commit to the remote repository (e.g., branch master on remote origin).
•	Response Example:

{ "status": "Git repository updated", "commit_oid": "abcdef1234567890..." }

Setup and Installation

Prerequisites • Rust: Install Rust by following the instructions at rust-lang.org/tools/install. • Dependencies: Ensure your Cargo.toml includes the following dependencies:

[dependencies] actix-web = "4" serde = { version = "1.0", features = ["derive"] } serde_json = "1.0" chrono = "0.4" git2 = "0.15"

Directory Structure

A suggested project structure:

autoscaler-api/ ├── Cargo.toml └── src/ └── main.rs

Running the Server 1. Build the project:

cargo build --release

2.	Run the server:

cargo run --release

The API will be available at http://127.0.0.1:8080/.

Testing and Debugging • Testing Endpoints: Use tools like curl or Postman to test and interact with the endpoints. • Logging: For production use, consider integrating logging middleware (such as with the env_logger crate) to capture detailed logs and debug information. • Enhancing Error Handling: The current error handling is basic. Enhance it further based on your needs for better error reporting and debugging.

Authentication and Security Considerations • Authentication: Secure your API endpoints with OAuth2, JWT tokens, or API keys, especially the Git update endpoint to prevent unauthorized changes. • Git Credentials: Use environment variables or a secure secret management system to manage Git repository authentication instead of hardcoding credentials. • Rate Limiting: Add rate limiting middleware to protect against abuse and DoS attacks.

Extending and Contributing • Adding New Features: Extend the API endpoints or add new ones (for example, direct integration with Kubernetes for live scaling actions) by following the existing structure. • Contributing: Contributions are welcome. Fork the repository, make your changes, and submit a pull request.

License

This project is distributed under the MIT License. See the LICENSE file for details.

Full Source Code

Below is the complete source code for the Custom Autoscaler API implemented in Rust using Actix Web:

use actix_web::{get, post, put, web, App, HttpResponse, HttpServer, Responder}; use chrono::Utc; use git2::{Repository, Signature}; use serde::{Deserialize, Serialize}; use std::sync::Mutex; use std::{fs, path::Path};

// --- Structures for API responses and requests ---

#[derive(Serialize)] struct HealthResponse { status: String, timestamp: String, }

#[derive(Serialize)] struct MetricsResponse { cpu_usage: String, memory_usage: String, current_replicas: u32, target_replicas: u32, metric_timestamp: String, }

#[derive(Deserialize)] struct AutoscaleRequest { resource: String, namespace: String, target_replicas: u32, }

#[derive(Serialize)] struct AutoscaleResponse { status: String, resource: String, namespace: String, new_replica_count: u32, timestamp: String, }

#[derive(Serialize, Deserialize, Clone)] struct Config { min_replicas: u32, max_replicas: u32, scale_up_threshold: u32, scale_down_threshold: u32, cool_down_period: u32, }

#[derive(Serialize)] struct ConfigResponse { status: String, updated_config: Config, timestamp: String, }

// Request structure for Git repository update. #[derive(Deserialize)] struct GitUpdateRequest { /// Relative path to the file in the repo to update (e.g., "manifests/mariadb.yaml"). file_path: String, /// New content to write into the file. new_content: String, /// Commit message for the change. commit_message: String, }

// Shared application state for holding configuration values. struct AppState { config: Mutex, }

// --- API Endpoint Handlers ---

// Health check endpoint (GET /health) #[get("/health")] async fn health() -> impl Responder { let now = Utc::now().to_rfc3339(); let response = HealthResponse { status: "OK".to_string(), timestamp: now, }; HttpResponse::Ok().json(response) }

// Metrics retrieval endpoint (GET /metrics) #[get("/metrics")] async fn get_metrics() -> impl Responder { let now = Utc::now().to_rfc3339(); let metrics = MetricsResponse { cpu_usage: "65%".to_string(), memory_usage: "1.2Gi".to_string(), current_replicas: 3, target_replicas: 4, metric_timestamp: now, }; HttpResponse::Ok().json(metrics) }

// Autoscale trigger endpoint (POST /autoscale) #[post("/autoscale")] async fn autoscale(req: web::Json) -> impl Responder { let now = Utc::now().to_rfc3339(); let response = AutoscaleResponse { status: "Scaling initiated".to_string(), resource: req.resource.clone(), namespace: req.namespace.clone(), new_replica_count: req.target_replicas, timestamp: now, }; HttpResponse::Ok().json(response) }

// Retrieve current autoscaler configuration (GET /config) #[get("/config")] async fn get_config(data: web::Data) -> impl Responder { let config = data.config.lock().unwrap(); HttpResponse::Ok().json(&*config) }

// Update autoscaler configuration (PUT /config) #[put("/config")] async fn update_config(new_config: web::Json, data: web::Data) -> impl Responder { let mut config = data.config.lock().unwrap(); *config = new_config.into_inner(); let now = Utc::now().to_rfc3339(); let response = ConfigResponse { status: "Configuration updated".to_string(), updated_config: config.clone(), timestamp: now, }; HttpResponse::Ok().json(response) }

// Git repository update endpoint (POST /git/update) #[post("/git/update")] async fn git_update(req: web::Json) -> impl Responder { // Path to the local clone of your Git repository. // Ensure that this path is correct and the repo is set up for pushing changes. let repo_path = "/path/to/your/local/repo"; let file_relative_path = &req.file_path; let full_file_path = format!("{}/{}", repo_path, file_relative_path);

// Attempt to write the new content to the file.
if let Err(e) = fs::write(&full_file_path, &req.new_content) {
    return HttpResponse::InternalServerError()
        .body(format!("Failed to write file: {}", e));
}

// Open the local repository.
let repo = match Repository::open(repo_path) {
    Ok(r) => r,
    Err(e) => return HttpResponse::InternalServerError().body(format!("Repo open error: {}", e)),
};

// Stage the file (add it to the Git index).
let mut index = match repo.index() {
    Ok(idx) => idx,
    Err(e) => return HttpResponse::InternalServerError().body(format!("Index error: {}", e)),
};

if let Err(e) = index.add_path(Path::new(file_relative_path)) {
    return HttpResponse::InternalServerError().body(format!("Failed to add path: {}", e));
}
if let Err(e) = index.write() {
    return HttpResponse::InternalServerError().body(format!("Failed to write index: {}", e));
}

// Write the index to a tree.
let tree_oid = match index.write_tree() {
    Ok(oid) => oid,
    Err(e) => return HttpResponse::InternalServerError().body(format!("Tree write error: {}", e)),
};
let tree = match repo.find_tree(tree_oid) {
    Ok(tree) => tree,
    Err(e) => return HttpResponse::InternalServerError().body(format!("Find tree error: {}", e)),
};

// Prepare a signature for the commit.
let signature = match repo.signature() {
    Ok(sig) => sig,
    Err(e) => return HttpResponse::InternalServerError().body(format!("Signature error: {}", e)),
};

// Find the current HEAD commit (if any).
let parent_commit = match repo.head() {
    Ok(reference) => reference.peel_to_commit().ok(),
    Err(_) => None,
};

// Create a commit.
let commit_result = if let Some(parent) = parent_commit {
    repo.commit(
        Some("HEAD"),
        &signature,
        &signature,
        &req.commit_message,
        &tree,
        &[&parent],
    )
} else {
    // First commit in the repository.
    repo.commit(
        Some("HEAD"),
        &signature,
        &signature,
        &req.commit_message,
        &tree,
        &[],
    )
};

let commit_oid = match commit_result {
    Ok(oid) => oid,
    Err(e) => return HttpResponse::InternalServerError().body(format!("Commit error: {}", e)),
};

// Push changes to the remote.
// This is a simplified push operation; in production you will need to handle authentication callbacks.
if let Ok(mut remote) = repo.find_remote("origin") {
    if let Err(e) = remote.push(&["refs/heads/master"], None) {
        return HttpResponse::InternalServerError().body(format!("Push error: {}", e));
    }
} else {
    return HttpResponse::InternalServerError().body("Failed to find remote 'origin'");
}

HttpResponse::Ok().json(serde_json::json!({
    "status": "Git repository updated",
    "commit_oid": commit_oid.to_string()
}))

}

// --- Main function to start the Actix Web server --- #[actix_web::main] async fn main() -> std::io::Result<()> { // Define initial configuration for the autoscaler. let init_config = Config { min_replicas: 2, max_replicas: 10, scale_up_threshold: 70, scale_down_threshold: 30, cool_down_period: 300, };

// Wrap configuration into shared state.
let state = web::Data::new(AppState {
    config: Mutex::new(init_config),
});

// Start the HTTP server at localhost on port 8080.
HttpServer::new(move || {
    App::new()
        .app_data(state.clone())
        .service(health)
        .service(get_metrics)
        .service(autoscale)
        .service(get_config)
        .service(update_config)
        .service(git_update)
})
.bind(("127.0.0.1", 8080))?
.run()
.await

}

Conclusion

This documentation describes the design and usage of a custom autoscaler API in Rust with Actix Web. It covers: • A detailed overview and architecture • Explanations of each API endpoint with sample requests and responses • Setup, installation, and running instructions • Security and testing considerations • Full source code for a ready-to-use implementation

Feel free to extend or modify this documentation and source code to fit your project’s specific needs.

Happy coding!

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