SIDECAR-PATTERN

Companion container in the same K8s pod.

Definition

The sidecar pattern offloads cross-cutting concerns (TLS, observability, secrets) from application code. Classic examples: Envoy (Istio mTLS), Fluentd (log forwarding), Vault Agent (secret injection), Prometheus node exporter, Consul Connect proxy. Kubernetes Sidecar Containers (KEP-753) GA in 1.29 (Dec 2023).

Origin

Concept formalised in Microsoft Cloud Design Patterns ; popularised by Bilgin Ibryam and Kubernetes in 2017.

Example in context

A Java app consumes a Vault secret via a Vault Agent sidecar refreshing /vault/secrets/db-creds hourly.

Related terms

• Ambassador — related pattern.