Allow setting of global defaults for some values

This helps with reducing redundant config.

Note: There is no default for `alert_every` because the zero value has a
meaning and cannot be interpreted as an omission.

README.md

@@ -55,6 +55,9 @@ The global configurations are:
 |key|value|
 |---|---|
 |`check_interval`|Maximum frequency to run checks for each monitor as duration, eg. 1m2s.|
+|`default_alert_after`|A default value used as an `alert_after` value for a monitor if not specified or 0.|
+|`default_alert_down`|Default down alerts to used by a monitor in case none are provided.|
+|`default_alert_up`|Default up alerts to used by a monitor in case none are provided.|
 |`monitors`|List of all monitors. Detailed description below|
 |`alerts`|List of all alerts. Detailed description below|
 

config.go

@@ -14,6 +14,9 @@ var errInvalidConfig = errors.New("Invalid configuration")
 // Config type is contains all provided user configuration
 type Config struct {
 	CheckInterval     SecondsOrDuration `yaml:"check_interval"`
+	DefaultAlertAfter int16             `yaml:"default_alert_after"`
+	DefaultAlertDown  []string          `yaml:"default_alert_down"`
+	DefaultAlertUp    []string          `yaml:"default_alert_up"`
 	Monitors          []*Monitor
 	Alerts            map[string]*Alert
 }
@@ -135,8 +138,23 @@ func (config Config) IsValid() (isValid bool) {
 
 // Init performs extra initialization on top of loading the config from file
 func (config *Config) Init() (err error) {
+	for _, monitor := range config.Monitors {
+		if monitor.AlertAfter == 0 && config.DefaultAlertAfter > 0 {
+			monitor.AlertAfter = config.DefaultAlertAfter
+		}
+
+		if len(monitor.AlertDown) == 0 && len(config.DefaultAlertDown) > 0 {
+			monitor.AlertDown = config.DefaultAlertDown
+		}
+
+		if len(monitor.AlertUp) == 0 && len(config.DefaultAlertUp) > 0 {
+			monitor.AlertUp = config.DefaultAlertUp
+		}
+	}
+
 	for name, alert := range config.Alerts {
 		alert.Name = name
+
 		if err = alert.BuildTemplates(); err != nil {
 			return
 		}

config_test.go

@@ -14,6 +14,7 @@ func TestLoadConfig(t *testing.T) {
 		pyCompat   bool
 	}{
 		{"./test/valid-config.yml", false, "Valid config file", false},
+		{"./test/valid-config-default-values.yml", false, "Valid config file with default values", false},
 		{"./test/valid-default-log-alert.yml", false, "Valid config file with default log alert PyCompat", true},
 		{"./test/valid-default-log-alert.yml", true, "Invalid config file no log alert", false},
 		{"./test/does-not-exist", true, "Invalid config path", false},

test/valid-config-default-values.yml

@@ -0,0 +1,12 @@
+---
+check_interval: 1
+default_alert_down: ["log_command"]
+default_alert_after: 1
+
+monitors:
+  - name: Command
+    command: ["echo", "$PATH"]
+
+alerts:
+  log_command:
+    command: ["echo", "regular", '"command!!!"', "{{.MonitorName}}"]