Created new term "Sidecar Container"

content/en/sidecar-container.md

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+---
+title: Sidecar Container
+status: Feedback Appreciated
+category: concept
+---
+
+The Sidecar Container is an implementation of the sidecar pattern. 
+An application deployed on a second container will run side by side 
+and share its lifecycle with a primary application running on a main container. 
+
+## Problem it addresses
+
+There are scenarios where it is convenient to group [containers](/container/) 
+to deal with cross-platform requirements or shared functionality.
+Such scenarios include [observability](/observability/) topics 
+like logging, monitoring, tracing, but also security, and networking. 
+For example, when multiple microservices have their sidecar containers 
+acting as logging agents to collect and forward logs to a log server, 
+or collecting metrics to forward to a monitoring system.
+
+## How it helps
+
+The term "sidecar" comes from the representation of a classic motorcycle 
+with its attached sidecar. 
+In this metaphor, the bike represents the main container 
+and the sidecar the secondary container. 
+This approach consists of using a separated process 
+running on a secondary container to address problems 
+that aren't unique to a single application 
+but rather to the entire platform where the application is running. 
+The Sidecar Container will share the same resources, 
+- storage, networking - as the main container. 
+While doing this, it frees the main container to be focused on functional tasks 
+or exposing business capabilities. 
+As a secondary container, the "sidecar" takes care of platform related tasks 
+such as logging, monitoring or security.   
+It enforces the principle of separation of concerns 
+and provides extending functionality without changing the main application's code.