Add support for environment variables in configuration file

config/config.go

@@ -64,6 +64,9 @@ func readConfigurationFile(fileName string) (config *Config, err error) {
 }
 
 func parseAndValidateConfigBytes(yamlBytes []byte) (config *Config, err error) {
+	// Expand environment variables
+	yamlBytes = []byte(os.ExpandEnv(string(yamlBytes)))
+	// Parse configuration file
 	err = yaml.Unmarshal(yamlBytes, &config)
 	// Check if the configuration file at least has services.
 	if config == nil || len(config.Services) == 0 {

config/config_test.go

@@ -13,12 +13,12 @@ services:
     url: https://twinnation.org/actuator/health
     interval: 15s
     conditions:
-      - "$STATUS == 200"
+      - "[STATUS] == 200"
   - name: github
     url: https://api.github.com/healthz
     conditions:
-      - "$STATUS != 400"
-      - "$STATUS != 500"
+      - "[STATUS] != 400"
+      - "[STATUS] != 500"
 `))
 	if err != nil {
 		t.Error("No error should've been returned")
@@ -53,7 +53,7 @@ services:
   - name: twinnation
     url: https://twinnation.org/actuator/health
     conditions:
-      - "$STATUS == 200"
+      - "[STATUS] == 200"
 `))
 	if err != nil {
 		t.Error("No error should've been returned")
@@ -76,7 +76,7 @@ services:
   - name: twinnation
     url: https://twinnation.org/actuator/health
     conditions:
-      - "$STATUS == 200"
+      - "[STATUS] == 200"
 `))
 	if err != nil {
 		t.Error("No error should've been returned")