What is the purpose and function of sidecars in web applications?

Sidecars are auxiliary containers or processes that run alongside the main application in a pod (for example, in Kubernetes). Their purpose is to extend or complement the main application's functionality without changing its code.

Main functions of sidecars:

• Logging and log aggregation
• Monitoring and metrics collection
• Configuration management and updates
• Proxying and traffic routing (e.g., service mesh)
• Caching or buffering data

Example: In service meshes (Istio, Linkerd), sidecars act as proxies intercepting all incoming and outgoing traffic, providing security, load balancing, and request tracing without modifying the main application.