config.go

/*
Package config contains convenience functions for reading and managing viper configs.

Copyright 2018 Google LLC

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package config

import (
	"github.com/fsnotify/fsnotify"
	log "github.com/sirupsen/logrus"
	"github.com/spf13/viper"
	"go.opencensus.io/stats"
	"go.opencensus.io/stats/view"
)

var (
	// Logrus structured logging setup
	logFields = log.Fields{
		"app":       "openmatch",
		"component": "config",
	}
	cfgLog = log.WithFields(logFields)

	// Map of the config file keys to environment variable names populated by
	// k8s into pods. Examples of redis-related env vars as written by k8s
	// REDIS_SENTINEL_PORT_6379_TCP=tcp://10.55.253.195:6379
	// REDIS_SENTINEL_PORT=tcp://10.55.253.195:6379
	// REDIS_SENTINEL_PORT_6379_TCP_ADDR=10.55.253.195
	// REDIS_SENTINEL_SERVICE_PORT=6379
	// REDIS_SENTINEL_PORT_6379_TCP_PORT=6379
	// REDIS_SENTINEL_PORT_6379_TCP_PROTO=tcp
	// REDIS_SENTINEL_SERVICE_HOST=10.55.253.195
	//
	// MMFs are expected to get their configuation from env vars instead
	// of reading the config file.  So, config parameters that are required
	// by MMFs should be populated to env vars.
	envMappings = map[string]string{
		"redis.user":             "REDIS_USER",
		"redis.password":         "REDIS_PASSWORD",
		"redis.hostname":         "REDIS_SERVICE_HOST",
		"redis.port":             "REDIS_SERVICE_PORT",
		"redis.pool.maxIdle":     "REDIS_POOL_MAXIDLE",
		"redis.pool.maxActive":   "REDIS_POOL_MAXACTIVE",
		"redis.pool.idleTimeout": "REDIS_POOL_IDLETIMEOUT",
		"api.mmlogic.hostname":   "OM_MMLOGICAPI_SERVICE_HOST",
		"api.mmlogic.port":       "OM_MMLOGICAPI_SERVICE_PORT",
	}

	// OpenCensus
	cfgVarCount = stats.Int64("config/vars_total", "Number of config vars read during initialization", "1")
	// CfgVarCountView is the Open Census view for the cfgVarCount measure.
	CfgVarCountView = &view.View{
		Name:        "config/vars_total",
		Measure:     cfgVarCount,
		Description: "The number of config vars read during initialization",
		Aggregation: view.Count(),
	}
)

// Read reads a config file into a viper.Viper instance and associates environment vars defined in
// config.envMappings
func Read() (View, error) {
	cfg := viper.New()
	// Viper config management initialization
	// Support either json or yaml file types (json for backwards compatibility
	// with previous versions)
	cfg.SetConfigType("json")
	cfg.SetConfigType("yaml")
	cfg.SetConfigName("matchmaker_config")
	cfg.AddConfigPath(".")
	cfg.AddConfigPath("config")

	// Read in config file using Viper
	err := cfg.ReadInConfig()
	if err != nil {
		cfgLog.WithFields(log.Fields{
			"error": err.Error(),
		}).Fatal("Fatal error reading config file")
	}

	// Bind this envvars to viper config vars.
	// https://github.com/spf13/viper#working-with-environment-variables
	// One important thing to recognize when working with ENV variables is
	// that the value will be read each time it is accessed. Viper does not
	// fix the value when the BindEnv is called.
	for cfgKey, envVar := range envMappings {
		err = cfg.BindEnv(cfgKey, envVar)

		if err != nil {
			cfgLog.WithFields(log.Fields{
				"configkey": cfgKey,
				"envvar":    envVar,
				"error":     err.Error(),
				"module":    "config",
			}).Warn("Unable to bind environment var as a config variable")

		} else {
			cfgLog.WithFields(log.Fields{
				"configkey": cfgKey,
				"envvar":    envVar,
				"module":    "config",
			}).Info("Binding environment var as a config variable")
		}
	}

	// Look for updates to the config; in Kubernetes, this is implemented using
	// a ConfigMap that is written to the matchmaker_config.yaml file, which is
	// what the Open Match components using Viper monitor for changes.
	// More details about Open Match's use of Kubernetes ConfigMaps at:
	// https://github.com/GoogleCloudPlatform/open-match/issues/42
	cfg.WatchConfig() // Watch and re-read config file.
	// Write a log when the configuration changes.
	cfg.OnConfigChange(func(event fsnotify.Event) {
		cfgLog.WithFields(log.Fields{
			"filename":  event.Name,
			"operation": event.Op,
		}).Info("Server configuration changed.")
	})
	return cfg, err
}