nsideris/shawarma

A Kubernetes sidecar to assist with enabling/disabling background processing during blue/green deployments.

Shawarma

A Kubernetes sidecar to assist with enabling/disabling background processing during blue/green deployments.

Overview

A Blue/Green Deployment is a process designed to maintain 100% uptime during deployments, with rapid rollbacks. As the new version is deployed, traffic is routed to the new version and diverted from the old version. However, the old version is left running and ready to receive traffic, allowing for rapid failover to the previous version in the event a rollback is required.

This works great for serving incoming requests, but what about background processes running within the application? For example, running scheduled background jobs or processing messages from the message bus. In a traditional blue/green deployment, these processes continue to execute, potentionally leaving a bug operating in production that you thought you fixed.

How it Works

Shawarma is designed to address this problem for applications running within Kubernetes. It is a very lightweight Go app which runs in a sidecar container within each pod of your application. It monitors the Kubernetes API to know when the pod is or is not connected to the load balancer, and uses an HTTP POST to let your application know the state. Your application must simply receive the POST and start or stop background processing.

Example

To see an example deployment utilizing Shawarma, see (./example/basic/example.yaml).

For a more automated example using annotations to automatically inject sidecars, see (./example/injected).

RBAC Rights

Shawarma requires access rights, via a service account, to monitor endpoints with the pod's namespace. It is recommended to create a single Role named `shawarma' in the namespace, and then bind it to each service account using a RoleBinding.

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: shawarma
rules:
- apiGroups: [""]
  resources: ["endpoints"]
  verbs: ["get", "watch", "list"]

Usage

shawarma monitor [arguments...]

Shawarma only functions within Kubernetes, using service tokens for authentication, so normally it is run using the Docker container centeredge/shawarma.

For detailed help:

docker run --rm -it centeredge/shawarma monitor --help

Arguments

Most arguments can be specified either on the command line, or via an environment variable. If specified both places, the command line takes precendence.

Name	Env Var	Description
--log-level	LOG_LEVEL	Set the log level (panic, fatal, error, warn, info, debug, trace) (default: "warn")
--namespace	MY_POD_NAMESPACE	Kubernetes namespace, typically a fieldRef to fieldPath: metadata.namespace
--pod	MY_POD_NAME	Kubernetes pod name, typically a fieldRef to fieldPath: metadata.name
--service	SHAWARMA_SERVICE	Name of the Kubernetes service to monitor
--url	SHAWARMA_URL	URL which receives a POST on state change, default: http://localhost/applicationstate