If env var is not defined, just log a warning

cloudprober.go

@@ -162,7 +162,7 @@ func InitFromConfig(configFile string) error {
 		return err
 	}
 
-	cfg, parsedConfigStr, err := config.ParseConfig(configStr, configFormat, sysvars.Vars())
+	cfg, parsedConfigStr, err := config.ParseConfig(configStr, configFormat, sysvars.Vars(), globalLogger)
 	if err != nil {
 		return err
 	}

config/config.go

@@ -34,7 +34,7 @@ var (
 	configFile = flag.String("config_file", "", "Config file")
 )
 
-var envRegex = regexp.MustCompile(`{{ secret:\$([^$]+) }}`)
+var envRegex = regexp.MustCompile(`\*\*\$([^$]+)\*\*`)
 
 const (
 	configMetadataKeyName = "cloudprober_config"
@@ -142,7 +142,7 @@ func DumpConfig(fileName, outFormat string, baseVars map[string]string) ([]byte,
 		return nil, err
 	}
 
-	cfg, _, err := ParseConfig(content, configFormat, baseVars)
+	cfg, _, err := ParseConfig(content, configFormat, baseVars, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -164,10 +164,10 @@ func DumpConfig(fileName, outFormat string, baseVars map[string]string) ([]byte,
 }
 
 // substEnvVars substitutes environment variables in the config string.
-func substEnvVars(configStr string) (string, error) {
+func substEnvVars(configStr string, l *logger.Logger) string {
 	m := envRegex.FindAllStringSubmatch(configStr, -1)
 	if len(m) == 0 {
-		return configStr, nil
+		return configStr
 	}
 
 	var envVars []string
@@ -180,25 +180,21 @@ func substEnvVars(configStr string) (string, error) {
 
 	for _, v := range envVars {
 		if os.Getenv(v) == "" {
-			return "", fmt.Errorf("environment variable %s not defined", v)
+			l.Warningf("Environment variable %s not defined, skipping substitution.", v)
+			continue
 		}
 		configStr = envRegex.ReplaceAllString(configStr, os.Getenv(v))
 	}
 
-	return configStr, nil
+	return configStr
 }
 
-func ParseConfig(content, format string, vars map[string]string) (*configpb.ProberConfig, string, error) {
+func ParseConfig(content, format string, vars map[string]string, l *logger.Logger) (*configpb.ProberConfig, string, error) {
 	parsedConfig, err := ParseTemplate(content, vars, nil)
 	if err != nil {
 		return nil, "", fmt.Errorf("error parsing config file as Go template. Err: %v", err)
 	}
 
-	finalConfigStr, err := substEnvVars(parsedConfig)
-	if err != nil {
-		return nil, "", fmt.Errorf("error substituting secret environment variables in the config string. Err: %v", err)
-	}
-
-	cfg, err := configToProto(finalConfigStr, format)
+	cfg, err := configToProto(substEnvVars(parsedConfig, l), format)
 	return cfg, parsedConfig, err
 }

config/config_test.go

@@ -15,12 +15,15 @@
 package config
 
 import (
+	"bytes"
+	"context"
 	"encoding/json"
 	"os"
 	"strings"
 	"testing"
 
 	configpb "github.com/cloudprober/cloudprober/config/proto"
+	"github.com/cloudprober/cloudprober/logger"
 	probespb "github.com/cloudprober/cloudprober/probes/proto"
 	surfacerspb "github.com/cloudprober/cloudprober/surfacers/proto"
 	targetspb "github.com/cloudprober/cloudprober/targets/proto"
@@ -226,7 +229,7 @@ func TestSubstEnvVars(t *testing.T) {
 		name      string
 		configStr string
 		want      string
-		wantErr   bool
+		wantLog   string
 	}{
 		{
 			name:      "no_env_vars",
@@ -235,25 +238,22 @@ func TestSubstEnvVars(t *testing.T) {
 		},
 		{
 			name:      "env_var",
-			configStr: `probe {name: "{{ secret:$SECRET_PROBE_NAME }}"}`,
+			configStr: `probe {name: "**$SECRET_PROBE_NAME**"}`,
 			want:      `probe {name: "probe-x"}`,
 		},
 		{
 			name:      "env_var_not_defined",
-			configStr: `probe {name: "{{ secret:$SECRET_PROBEX_NAME }}"}`,
-			wantErr:   true,
+			configStr: `probe {name: "**$SECRET_PROBEX_NAME**"}`,
+			want:      `probe {name: "**$SECRET_PROBEX_NAME**"}`,
+			wantLog:   "SECRET_PROBEX_NAME not defined",
 		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			got, err := substEnvVars(tt.configStr)
-			if (err != nil) != tt.wantErr {
-				t.Errorf("substEnvVars() error = %v, wantErr %v", err, tt.wantErr)
-				return
-			}
-			if got != tt.want {
-				t.Errorf("substEnvVars() = %v, want %v", got, tt.want)
-			}
+			var buf bytes.Buffer
+			l, _ := logger.New(context.Background(), "config_test", logger.WithWriter(&buf))
+			assert.Equal(t, tt.want, substEnvVars(tt.configStr, l))
+			assert.Contains(t, buf.String(), tt.wantLog)
 		})
 	}
 }

config/config_tmpl.go

@@ -188,7 +188,7 @@ func ParseTemplate(config string, sysVars map[string]string, getGCECustomMetadat
 			}
 			return matches[n], nil
 		},
-		"envSecret": func(s string) string { return "{{ secret:$" + s + " }}" },
+		"envSecret": func(s string) string { return "**$" + s + "**" },
 	}
 
 	for name, f := range sprig.TxtFuncMap() {

config/config_tmpl_test.go

@@ -73,7 +73,7 @@ func TestParseTemplate(t *testing.T) {
 				}
 				}
 			`,
-			wantProbes:  []string{"{{ secret:$SECRET_PROBE_NAME }}"},
+			wantProbes:  []string{"**$SECRET_PROBE_NAME**"},
 			wantTargets: []string{"host_names:\"www.google.com\""},
 		},
 		{