# Controllers

Istio has a variety of [controllers](https://kubernetes.io/docs/concepts/architecture/controller/), which basically watch some inputs and do something.
This can be reading from Kubernetes and writing other objects back, writing to proxies over XDS, etc.

Unfortunately, writing controllers is very error prone, even for seemingly simple cases.
To work around this, Istio has a variety of abstractions meant to make writing controllers easier.

## Clients

	viper.SetConfigName(configName)
	viper.SetConfigType(configType)
	viper.AddConfigPath(configPath)
	viper.SetEnvKeyReplacer(strings.NewReplacer("-", "_"))
	err := viper.ReadInConfig()
	// Ignore errors reading the configuration unless the file is explicitly customized
	if root.IstioConfig != defaultIstioctlConfig {
		return err
	}

	return nil
}

func init() {

# any Mac or Linux platform with bash 4.2+. Please take care not to modify this function
# without testing properly.
#
# This function will properly handle any type of path including those with spaces using the
# loading pattern specified by *kubectl config*.
#
# testcase: "a:b c:d"
# testcase: "a b:c d:e f"
# testcase: "a b:c:d e"
parse_KUBECONFIG () {
TMPDIR=""
if [[ "$1" =~ ([^:]*):(.*) ]]; then
  while true; do

## Introduction

This document covers primarily the code, with some background on how the design maps to it.
See the
[design doc](https://docs.google.com/document/d/11j9ZtYWNWnxQYnZy8ayZav1FMwTH6F6z6fkDYZ7V298/edit#heading=h.qex63c29z2to)
for a more complete design description. The operator code is divided roughly into five areas:

1. [IstioOperatorSpec API](#istiooperatorspec-api) and related infrastructure, which is expressed as a

	// 3. inject label false
	// 4. inject label true and revision label
	// 5. inject label false and revision label
	// 6. no label
	// However, we filter out all the disable cases, leaving us with a reasonable number of cases
	testLabels := []LabelSet{}
	for _, namespaceLabel := range []klabels.Set{empty, revLabel, legacyLabel, legacyLabelDisabled, legacyAndRevLabel, legacyDisabledAndRevLabel} {