From Clients to Servers: Understanding Forward and Reverse Proxies

In computer networks setup, proxies play a crucial role in controlling and enabling conversation between servers and clients. Fundamentally, a proxy is an intermediary that stands between a client and a server. There are two main types of proxies — forward proxy and reverse proxy. Understanding these concepts is fundamental for any backend developer as they are essential elements in managing network communication, enhancing security, and optimizing performance of web servers.

Proxy Server:

A proxy server, often simply referred to as a “proxy”, is a server that acts as an intermediary for requests from clients seeking resources from other servers. Clients connect to the proxy server, requesting some service, such as a file, connection, web page or other resources available from a different server.

Forward Proxy:

A forward proxy, often simply known as a ‘proxy’, is what most people think of when they hear the term proxy. When a client program or, in simpler terms, a user, makes a request that a forward proxy server can fulfill, the proxy serves the request on behalf of the user.

Reverse Proxy:

Contrastingly, a reverse proxy, also known as a ‘backward proxy’, is a type of proxy server that routes client requests to appropriate backend servers, thereby providing a smoother flow of network traffic.

As a backend developer, you don’t always need to directly code a proxy server. However, you should be aware of libraries that allow you to integrate with one such as Apache HttpClient for Java.

CloseableHttpClient httpclient = HttpClients.createDefault();
try {
    HttpHost target = new HttpHost("http://mybackend.com", 443, "https");
    HttpHost proxy = new HttpHost("http://myproxy.com", 8080, "http");

    RequestConfig config = RequestConfig.custom()
        .setProxy(proxy)
        .build();
    HttpGet httpget = new HttpGet("/");
    httpget.setConfig(config);

    CloseableHttpResponse response = httpclient.execute(target, httpget);
    try {
        HttpEntity entity = response.getEntity();

        if (entity != null) {
            long len = entity.getContentLength();
            System.out.println(EntityUtils.toString(entity));
        }
    } finally {
        response.close();
    }
} finally {
    httpclient.close();
}

In a typical scenario, your client (Web browser) connects to the forward proxy server. The forward proxy server, then, forwards your request to the Web server (target server). The Web server sees the proxy server simply as a client, so it sends responses back to the proxy server, which then passes them back along to the original client.

In a reverse proxy scenario, the client connects to the reverse proxy server, which then determines where to send the client’s request among several associated servers. The selected server sends its responses back to the reverse proxy server, which then sends them back to the client. In this case, the client sees the reverse proxy server as the Web server.

Real-World Applications

Both forward and reverse proxies are used extensively in real-world applications. Forward proxies are primarily used to bypass geoblocking or other types of content restrictions, as well as to maintain internet security and privacy. Large enterprises often use forward proxies to ensure all internet traffic from their networks passes through a single point, which is controlled and monitored for security purposes.

Reverse proxies, on the other hand, are often found in web servers where they boost performance through load-balancing, thus ensuring the web applications maintain optimal speed and performance.

Common Pitfalls:

A common pitfall often associated with the use of forward proxy is the disregard for privacy. When you transmit sensitive information via a forward proxy that isn’t secure, your data can potentially be accessed by the proxy operator.

When using reverse proxies, they can introduce single points of failure into your architecture if not properly load balanced with multiple instances.

Summary:

• Proxies are intermediaries standing between clients and servers with two types: forward and reverse proxies.
• Forward proxies serve client requests on behalf of the client.
• Reverse proxies route client requests to appropriate backend servers.
• Direct coding for a proxy server is rare, but as a backend developer, you should be aware of how to configure libraries to integrate with one.
• Forward proxies are commonly used for content access and control, and internet security.
• Reverse proxies are used mostly to effect load balancing and to ensure optimal web application speeds and performance.
• Mismanagement and misconfiguration of both proxy types can potentially expose networks and data to security vulnerabilities.