Configuration

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Configuration

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Essential & Non-trivial: Config!

One of the most confusing aspects of building web services, especially those that are automatically deployed into a container orchestration platform (like Kubernetes or AWS' ECS) via Docker, is configuration!

For this purpose, we will use environment variables exclusively, as this is the industry standard! When it comes to managing files (or larger configuration values) you might be able to get away with Base64-encoding them into environment variables and then decoding them as part of your configuration init process, and that can work well with things like key files since they are relatively small, however, larger config files likely must be managed by your orchestration platform and that's out of the scope of this course.

Env Vars in Go

You can always get an env var with os.GetEnv("VAR_NAME") in Go, however, for managing an entire config struct with defaults, we will use a library called 'envconfig' available here.

Logging

We'll cover logging more later, however, you will notice that we'll use the logrus 3rd party logger for sending structured logs to our stdout

Our config.go file

This is where we will manage our config in config/config.go:

package config
            
            import (
                "fmt"
                "github.com/exlinc/golang-utils/envconfig"
                "github.com/sirupsen/logrus"
            )
            
            // The envconfig struct tag is used to explicitly name the var, set defaults, and flag required values
            type Config struct {
                DBPath          string   `envconfig:"DB_PATH" required:"true"`
                Mode            string   `envconfig:"MODE" default:"production"`
                ListenAddress   string   `envconfig:"LISTEN_ADDRESS" default:"0.0.0.0"`
                ListenPort      string   `envconfig:"LISTEN_PORT" default:"3333"`
                AllowedOrigins  []string `envconfig:"ALLOWED_ORIGINS" default:"*"`
                ServiceAPIKey   string   `envconfig:"SERVICE_API_KEY" default:"insecure"`
                TokenCookieName string   `envconfig:"TOKEN_COOKIE_NAME" default:"auth_tkn"`
            }
            
            var conf *Config
            
            const (
                DebugMode      = "debug"
                ProductionMode = "production"
            )
            
            // This function gets called automatically when the package is loaded
            func init() {
                conf = &Config{}
                // This prefix means our variables will be in the form of GDEMO_MODE (for example)
                err := envconfig.Process("GDEMO", conf)
                if err != nil {
                    fmt.Println("Fatal error processing configuration")
                    panic(err)
                }
                l := conf.GetLogger()
            
                // Sanity check
                if !conf.IsDebugMode() && !conf.IsProductionMode() {
                    l.Fatal("Invalid GDEMO_MODE variable, it must be either `debug` or `production`")
                }
            }
            
            // Cfg returns the configuration - will panic if the config has not been loaded or is nil (which shouldn't happen as that's implicit in the package init)
            func Cfg() *Config {
                if conf == nil {
                    panic("Config is nil")
                }
                return conf
            }
            
            func (cfg *Config) GetLogger() *logrus.Logger {
                var l = logrus.New()
                l.Formatter = &logrus.JSONFormatter{}
                return l
            }
            
            func (cfg *Config) IsDebugMode() bool {
                return cfg.Mode == DebugMode
            }
            
            func (cfg *Config) IsProductionMode() bool {
                return cfg.Mode == ProductionMode
            }

Update deps

Since we added new dependencies in this file, remember to run dep ensure -v again to update our deps.

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