cic-stack/apps/util/liveness

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liveness (Untitled Document)	global	makeinfo	liveness (Untitled Document)	en	document	liveness (Untitled Document)

[]{#liveness}[]{#liveness-1}

1 liveness

[]{#ilveness_005foverview}[]{#Overview}

1.1 Overview

This is a cluster-specific convenience setup for enabling a Kubernetes-style liveness/readiness test as outlined in https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/.

Conceptually, it provides an application with means to:

• Run a collection of functions to validate sanity of the environment
• Set a no-error state before execution of the main routine
• Modify the error state during execution
• Invalidating all state when execution ends

[]{#Python-module}

1.2 Python module

Three python methods are provided.

[]{#load}

1.2.1 load

This is meant to be called after configurations and environment has been set up, but before the execution logic has commenced.

It receives a list of externally defined fully-qualified python modules. Each of these modules must implement the method health(*args,**kwargs) in its global namespace.

Any module returning False will cause a RuntimeException.

The component will not trap any other exception from the modules.

If successful, it will write the pid of the application to the specified run data folder. By default this is /run/<HOSTNAME>, but the path can be modified if desired.

[]{#set}

1.2.2 set

This is meant to be called during the execution of the main program routine begins.

[]{#at-startup}

1.2.2.1 at startup

It should be called once at the start of execution of the main program routine.

For one-shot routines, this would mean the start of any code only run when the module name is __main__.

For daemons, it would be just before handing over execution to the main loop.

[]{#during-execution}

1.2.2.2 during execution

Call set(error_code=<error>, ... any time the health state temporarily changes. Any error value other than 0 is considered an unhealthy state.

[]{#at-shutdown}

1.2.2.3 at shutdown

Call reset(...), which will indicate that the state is to be considered the same as at startup.

[]{#shell}

1.3 shell

A bash script is provided for Kubernetes to perform the health check.

It performs the following checks:

1. A numeric value exists in <rundir>/<unitname>/pid{.sample}.
2. The numeric value is a directory in /proc{.sample} (a valid pid)
3. The file <rundir>/<unitname>/error{.sample} contains "0"

If any of these checks fail should inditcate that the container is unhealthy.

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