perimener

README

Perímener ✋

Named after the Greek word Perímene αναμονή for wait.

A golang application that waits for the expected number of pods to reach a Ready state before gracefully exiting.

Problem statement

Have you ever needed an initContainer which can perform simple dependency management.

Starting containers before their dependencies are ready can result in pods going into a status of CrashLoopBackoff these wastes resources which could have been used on the dependencies themselves.

An example of this might be ensuring that a number of zookeeper pods reach a Ready state before kafka is started.

Perímener also has functionality to avoid the thundering herd issue which is amplified when using GitOps principles.

Setting an environment variable inserts a random delay from 0 to <RANDOM_WINDOW_SECONDS> to application startup which can help prevent undesirable autoscaling events.

Usage

Configuration is done via the use of ENVIRONMENT variables

Environment variable Name	Parameter Function	Required/Default
DELAY_SECONDS	Delay start of the main container by n seconds	Default: 0 seconds (Disabled)
EXPECTED_READY_POD_COUNT	The number of pods to reach a Ready state before the init container will exit and allow the main container to start	Required
NAMESPACE	Which namespace to target	Required
POD_LABEL	A label selector which matches the required pods	Required
RANDOM_WINDOW_SECONDS	Max seconds for window size	Default: 0 seconds (Disabled)
SLEEP_COUNT	The time to wait between retries	Default: 5 seconds
USE_LOCAL_KUBECONFIG	Use a local kubeconfig or not. Defaults to in cluster auth	Default: false