When Sidecar pattern is useful ?

When the services/components are implemented with multiple languages or technologies.

A service/component must be co-located on the same container group (pod) or host where primary application is running.

A service/component is owned by remote team or different organization.

A service which can be independently updated without the dependency of the primary application but share the same lifecycle as primary application.

If we need control over resource limits for a component or service.

Examples:

1. Adding HTTPS to a Legacy Service

2. Dynamic Configuration with Sidecars

3. Log Aggregator with Sidecar

https://medium.com/nerd-for-tech/microservice-design-pattern-sidecar-sidekick-pattern-dbcea9bed783