Introduction To Distributed Systems

What are Distributed Systems?

Distributed systems are a model in which components located on networked computers communicate and coordinate their actions by passing messages. The components interact with each other in order to achieve a common goal. The key aspect of distributed systems is that they do not share a global clock, and the individual components may have their own local clocks, leading to potential synchronization issues.

Characteristics of Distributed Systems

Distributed systems have several key characteristics that define them:

Scalability: They can be easily scaled up or down depending on the workload.
Fault Tolerance: The system can continue to operate even if one or more components fail.
Concurrency: Multiple components can operate simultaneously, allowing for improved performance.
Transparency: The system hides the complexities of the distributed nature from users, making it appear as a single coherent system.

Types of Distributed Systems

There are several types of distributed systems, including:

Client-Server Systems: A centralized server provides resources or services to multiple clients.
Peer-to-Peer Systems: All nodes in the system have equal responsibilities and can act as both clients and servers.
Cloud Computing: Resources and services are provided over the internet, allowing for scalable and flexible resource usage.

Examples of Distributed Systems

Some common examples of distributed systems include:

Web Services: Services like Amazon Web Services (AWS) and Microsoft Azure provide distributed computing resources.
Content Delivery Networks (CDNs): These systems distribute content across multiple locations to improve access speed and reliability.
Database Systems: Distributed databases like Apache Cassandra allow for data to be stored across multiple nodes while ensuring consistency and availability.

Challenges in Distributed Systems

While distributed systems offer many advantages, they also present several challenges:

Network Issues: Latency, bandwidth limitations, and network failures can impact performance.
Data Consistency: Ensuring that all nodes have the same data can be complex, particularly in the presence of failures.
Security: Securing communications and data across distributed nodes is a significant concern.

Conclusion

Distributed systems are a fundamental aspect of modern computing, enabling scalability, fault tolerance, and efficient resource usage. Understanding the principles, characteristics, and challenges of distributed systems is crucial for designing and implementing effective applications in today's interconnected world.

Example Use Case: Memcached

Memcached is a distributed memory caching system that enhances the performance of dynamic web applications by alleviating database load. It is a key-value store that can be used to cache data and objects in RAM, providing quick access to frequently requested data. Here's a simple example:

Basic Memcached Setup

To install Memcached on a server, you can use the following command:

sudo apt-get install memcached

After installation, you can start the Memcached server with:

memcached -m 64 -p 11211 -u nobody

This command starts Memcached with a memory limit of 64MB, on port 11211, running under the user 'nobody'.

Using Memcached in a PHP Application

Here’s how you might interact with Memcached in a PHP application:

$memcache = new Memcache;
$memcache->connect('localhost', 11211);
$memcache->set('key', 'value', 0, 3600);
$value = $memcache->get('key');
echo $value; // Outputs 'value'