Author: Abhishek Dubey

I am Abhishek Dubey, a Senior Cloud Consultant at Opstree Solutions with a focus on cloud infrastructure, DevOps, and automation technologies. With extensive experience in cloud platforms like AWS, Azure, and Google Cloud, I specialize in building scalable and secure cloud environments that drive business efficiency. My expertise includes designing robust architectures, implementing CI/CD pipelines, and ensuring high availability and performance for enterprise applications.

Linux Namespaces – Part 1

Overview

First of all I would like to give credit to Docker which motivated me to write this blog, I’ve been using docker for more then 6 months but I always wondered how things are happening behind the scene. So I started in depth learning of Docker and here I am talking about Namespace which is the core concept used by Docker.

Before talking about Namespaces in Linux, it is very important to know that what namespaces actually is?

Let’s take an example, We have two people with the same first name Abhishek Dubey and Abhishek Rawat but we can differentiate them on the basis of their surname Dubey and Rawat. So you can think surname as a namespace.

In Linux, namespaces are used to provide isolation for objects from other objects. So that anything will happen in namespaces will remain in that particular namespace and doesn’t affect other objects of other namespaces. For example:- we can have the same type of objects in different namespaces as they are isolated from each other.

In short, due to isolation, namespaces limits how much we can see.

Now you would be having a good conceptual idea of Namespace let’s try to understand them in the context of Linux Operating System.

Linux Namespaces

Linux namespace forms a single hierarchy, with all processes and that is init. Usually, privileged processes and services can trace or kill other processes. Linux namespaces provide the functionality to have many hierarchies of processes with their own “subtrees”, such that, processes in one subtree can’t access or even know those of another.
A namespace wraps a global system resource (For ex:- PID) using the abstraction that makes it appear to processes within the namespace that they have, using their own isolated instance of the said resource.

In the above figure, we have a process named 1 which is the first PID and from 1 parent process there are new PIDs are generated just like a tree. If you see the 6th PID in which we are creating a subtree, there actually we are creating a different namespace. In the new namespace, 6th PID will be its first and parent PID. So the child processes of 6th PID cannot see the parent process or namespace but the parent process can see the child PIDs of the subtree.

Let’s take PID namespace as an example to understand it more clearly. Without namespace, all processes descend(move downwards) hierarchically from First PID i.e. init. If we create PID namespace and run a process in it, the process becomes the First PID in that namespace. In this case, we wrap a global system resource(PID). The process that creates the namespace still remains in the parent namespace but makes it child for the root of the new process tree.
This means that the processes within the new namespace cannot see the parent process but the parent process can see the child namespace process. 
I hope you have got a clear understanding of Namespaces concepts & what purpose they serve in a Linux OS. The next blog of this series will talk about how we use namespace to restrict usage of system resources such as network, mounts, cgroups…

    Forward and Reverse Proxy

    Overview

    Before talking about forward proxy and reverse proxy let’s talk about what is the meaning of proxy.
    Basically proxy means someone or something is acting on behalf of someone.
    In the technical realm, we are talking about one server is acting behalf of the other servers.

    In this blog, we will talk about web proxies. So basically we have two types of web proxies:-

    • Forward Proxy
    • Reverse Proxy
    The forward proxy is used by the client, for example:- web browser, whereas reverse proxy is used by the server such as web server.

    Forward Proxy

    In Forward Proxy, proxy retrieves data from another website on the behalf of original requestee. For example:- If an IP is blocked for visiting a particular website then the person(client) can use the forward proxy to hide the real IP of the client and can visit the website easily.
    Let’s take another example to understand it more clearly. For example, we have 3 server
    Client                      -> Your computer from which you are sending the request
    Proxy Site               -> The proxy server, proxy.example.com
    Main Web server    -> The website you want to see
    Normally connection can happen like this 
    In the forward proxy, the connection will happen like this
    So here the proxy client is talking to the main web server on the behalf of the client.
    The forward proxy also acts as a cache server. For example:- If the content is downloading multiple times the proxy can cache the content on the server so next time when another server is downloading the same content, the proxy will send the content that is previously stored on the server to another server. 

     Reverse Proxy

    The reverse proxy is used by the server to maintain load and to achieve high availability. A website may have multiple servers behind the reverse proxy. The reverse proxy takes requests from the client and forwards these requests to the web servers. Some tools for reverse proxy are Nginx, HaProxy.
    So let’s take the similar example as the forward proxy
    Client                      -> Your computer from which you are sending the request
    Proxy Site               -> The proxy server, proxy.example.com
    Main Web server    -> The website you want to see
    Here it is better to restrict the direct access to the Main Web Server and force the requests or requestors to go through Proxy Server first. So data is being retrieved by Proxy Server on the behalf of Client.
    • So the difference between Forward Proxy and Reverse Proxy is that in Reverse Proxy the user doesn’t know he is accessing Main Web Server, because of the user only communicate with Proxy Server.
    • The Main Web Server is invisible for the user and only Reverse Proxy Server is visible. The user thinks that he is communicating with Main Web Server but actually Reverse Proxy Server is forwarding the requests to the Main Web Server.