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72 lines
3.7 KiB
Markdown
72 lines
3.7 KiB
Markdown
# Graceful Service Node Shutdown Solution
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## 1. Core Objective
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Achieve graceful shutdown of service nodes, ensuring no in-flight user requests are lost during service termination while maintaining overall cluster availability.
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## 2. Solution Overview
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This solution combines **Nginx reverse proxy**, **Gunicorn server**, **Uvicorn server**, and **FastAPI** working in collaboration to achieve the objective.
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## 3. Component Introduction
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### 1. Nginx: Traffic Entry Point and Load Balancer
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- **Functions**:
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- Acts as a reverse proxy, receiving all external client requests and distributing them to upstream Gunicorn worker nodes according to load balancing policies.
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- Actively monitors backend node health status through health check mechanisms.
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- Enables instantaneous removal of problematic nodes from the service pool through configuration management, achieving traffic switching.
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### 2. Gunicorn: WSGI HTTP Server (Process Manager)
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- **Functions**:
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- Serves as the master process, managing multiple Uvicorn worker child processes.
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- Receives external signals (e.g., `SIGTERM`) and coordinates the graceful shutdown process for all child processes.
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- Daemonizes worker processes and automatically restarts them upon abnormal termination, ensuring service robustness.
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### 3. Uvicorn: ASGI Server (Worker Process)
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- **Functions**:
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- Functions as a Gunicorn-managed worker, actually handling HTTP requests.
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- Runs the FastAPI application instance, processing specific business logic.
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- Implements the ASGI protocol, supporting asynchronous request processing for high performance.
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---
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## Advantages
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1. **Nginx**:
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- Can quickly isolate faulty nodes, ensuring overall service availability.
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- Allows configuration updates without downtime using `nginx -s reload`, making it transparent to users.
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2. **Gunicorn** (Compared to Uvicorn's native multi-worker mode):
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- **Mature Process Management**: Built-in comprehensive process spawning, recycling, and management logic, eliminating the need for custom implementation.
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- **Process Daemon Capability**: The Gunicorn Master automatically forks new Workers if they crash, whereas in Uvicorn's `--workers` mode, any crashed process is not restarted and requires an external daemon.
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- **Rich Configuration**: Offers numerous parameters for adjusting timeouts, number of workers, restart policies, etc.
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3. **Uvicorn**:
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- Extremely fast, built on uvloop and httptools.
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- Natively supports graceful shutdown: upon receiving a shutdown signal, it stops accepting new connections and waits for existing requests to complete before exiting.
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---
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## Graceful Shutdown Procedure
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When a specific node needs to be taken offline, the steps are as follows:
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1. **Nginx Monitors Node Health Status**:
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- Monitors the node's health status by periodically sending health check requests to it.
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2. **Removal from Load Balancing**:
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- Modify the Nginx configuration to mark the target node as `down` and reload the Nginx configuration.
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- Subsequently, all new requests will no longer be sent to the target node.
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3. **Gunicorn Server**:
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- Monitors for stop signals. Upon receiving a stop signal (e.g., `SIGTERM`), it relays this signal to all Uvicorn child processes.
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4. **Sending the Stop Signal**:
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- Send a `SIGTERM` signal to the Uvicorn process on the target node, triggering Uvicorn's graceful shutdown process.
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5. **Waiting for Request Processing**:
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- Wait for a period slightly longer than `timeout_graceful_shutdown` before forcefully terminating the service, allowing the node sufficient time to complete processing all received requests.
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6. **Shutdown Completion**:
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- The node has now processed all remaining requests and exited safely.
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