01_web_server_overview

Web Server Overview

Backend engineers are responsible for setting up and maintaining servers that host web applications, APIs, and databases. A solid understanding of server management principles is crucial for delivering robust, high-performing, and secure systems.

Client-Server Architecture

Client-server architecture underpins most modern networked systems and the internet. It describes how clients (which request services) interact with servers (which provide these services).

          +-----------+            +-----------+
          |  Client 1 |            |  Client 2 |
          +-----+-----+            +-----+-----+
                ^                        ^
                |                        |
                |  Request/Response      |  Request/Response
                |                        |
                v                        ^
          +-----+-----+            +-----+-----+
          |           |            |           |
          |           +------------>           |
          |  Server   <------------+  Server   |
          |           |            |           |
          |           |            |           |
          +-----+-----+            +-----+-----+
                ^                        ^
                |                        |
                v                        ^
          +-----+-----+            +-----+-----+
          |  Client 3 |            |  Client 4 |
          +-----------+            +-----------+

Client
- Sends requests for data or services, typically through protocols like HTTP, FTP, or SMTP.
- Can be anything from a web browser to a mobile app or IoT device.
Server
- Receives and processes client requests, then returns appropriate responses.
- Could be a web server, database server, mail server, etc.
Communication
- Relies on a network (often the internet).
- Common protocols include HTTP for web traffic, FTP for file transfer, and SMTP for email.

Architecture Patterns

Two-Tier Architecture
- Direct communication between client and server.
- Suitable for simple setups or smaller user bases.
```
+--------+       +------------------+
| Client |  <--> |    Server (DB)   |
+--------+       +------------------+
```
Three-Tier Architecture
- Separates presentation (client), application (middle layer), and data (database) layers.
- Helps in organizing complex applications, enhancing security, and scaling individual layers independently.
```
+--------+       +------------------+       +------------------+
| Client |  <--> |   App Server     | <-->  |   Database       |
+--------+       +------------------+       +------------------+
```

N-Tier (Multi-Tier) Architecture

Adds more layers, such as separate microservices, caching servers, or specialized business logic layers.
Offers enhanced scalability, flexibility, and maintainability.

        +--------+
        | Client |
        +---+----+
            |
            v
 +-------------------+        +-------------------+
 |  Web Tier (API)   |  <-->  |  Business Logic   |
 +--------+----------+        +---------+---------+
           |                          |
           v                          v
 +-------------------+       +--------------------+
 |  Caching / Queue  |       |  Database / Storage|
 +-------------------+       +--------------------+

Advantages

Scalability: Servers can handle many clients concurrently.
Maintenance: Upgrading back-end services does not disrupt client applications.
Security: Central control over data and authentication.
Resource Sharing: Efficient usage of server hardware and software resources.

Disadvantages

Dependency: Clients rely on server uptime.
Network Dependency: Requires stable network connections.
Congestion: High load can overwhelm the server if not scaled properly.

Server Types

Servers can be provisioned in different ways depending on performance requirements, budget, and desired control:

Dedicated Servers
- A single physical machine dedicated to one application or client.
- High performance, maximum control, but often costlier.
Virtual Private Servers (VPS)
- A virtualized portion of a physical server.
- More affordable than dedicated servers, offering reasonable performance and control.
Cloud Servers
- Managed by cloud providers like AWS, Azure, or Google Cloud.
- Highly scalable and flexible, pay-as-you-go model.
- Cost can vary based on usage and resource consumption.

      +-----------+
      |  Client 1 |
      +-----+-----+
            |
            | HTTP Request
            v
+-----------------------+
|      Web Server       |
|-----------------------|
| - Hosts Web Pages     |
| - Processes Requests  |
| - Sends Responses     |
+-----------------------+
            ^
            | HTTP Response
            |
      +-----+-----+
      |  Client 2 |
      +-----------+

Operating Systems

Linux (Ubuntu, CentOS, Debian, etc.)
- Popular in server environments for stability, security, and open-source ecosystem.
- Powerful command-line tools, extensive community support.
Windows Server
- Chosen for .NET environments or for integrating with other Microsoft services.
- Graphical interfaces and Windows-centric tools.

Server Configuration

To run services effectively, servers require careful setup:

Web Server Software: Apache, Nginx, IIS, or others.
Database Servers: MySQL, PostgreSQL, MongoDB, etc.
Caching Systems: Redis or Memcached for faster data retrieval.
Language Runtimes/Frameworks: Node.js, Python, Ruby, Java, PHP.

Example Setup (Ubuntu + Nginx + Node.js + MongoDB)

Install OS: Start with Ubuntu as the server operating system.
Install Nginx: Configure it to serve static files and proxy requests to Node.js.
Install Node.js: Run the application logic or API.
Install MongoDB: Store and manage application data.
Configure Firewalls: Secure traffic, allowing only HTTP/HTTPS and SSH as needed.

Security

Securing a server is crucial to prevent unauthorized access and data breaches:

Firewalls: Configure iptables or ufw to control network traffic.
SSL/TLS Certificates: Use HTTPS for secure client-server communication.
User Access Control: Implement key-based SSH authentication, minimal open ports.
Regular Updates: Keep system packages and software patched.
Intrusion Detection: Tools like fail2ban or tripwire to monitor malicious activity.

Performance Tuning

Optimizing server performance involves balancing resource usage and application demands:

Load Balancing: Use reverse proxies (e.g., HAProxy, Nginx) or load balancers to distribute requests.
Caching: Implement in-memory caches or content caching to reduce repeated computation.
Resource Monitoring: Tools like top, htop, or nmon help identify CPU, RAM, or I/O bottlenecks.
Database Indexing: Proper indexes and query optimization for better query performance.

Backup and Disaster Recovery

A robust strategy ensures minimal downtime and data loss:

Regular Backups: Automate database snapshots and file backups (daily, weekly).
Redundancy: Set up replicas or high-availability clusters (e.g., MySQL replication).
Recovery Testing: Regularly test restoring backups to validate the process.

Automation and CI/CD

Streamlined development and deployment pipelines keep the server environment consistent and reliable:

Scripting: Use Bash, Python, or Ansible for repetitive admin tasks.
Continuous Integration: Tools like Jenkins, GitLab CI automate building and testing code changes.
Continuous Deployment: Deploy updates quickly and safely to staging or production.

Monitoring and Alerts

Detecting and responding to issues quickly is essential:

Monitoring Tools: Nagios, Prometheus, Grafana for real-time metrics and alerting.
Log Management: ELK Stack (Elasticsearch, Logstash, Kibana) for centralizing and analyzing logs.
Alerts: Configure email/SMS/Slack alerts for system anomalies, such as high CPU usage or downtime.

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