feat: Add support for using env vars in config

docs/setup.md

@@ -181,6 +181,25 @@ chains:
         grpc: 'grpc-axelar.endpoint.xyz:9090'
 ```
 
+## Example Using Environment Variables
+Environment variables can be used to inject values into the configuration file. 
+For this a simple template variable marked by `${}` (e.g. `${SUPER_SECRET_ENV_VAR}`) can be added to the config file.
+
+```yaml
+monikers: ['all']
+
+chains:
+  - display_name: 'cosmos'
+    chain_id: cosmoshub-4
+    tracking_addresses:
+      - 'cosmos1clpqr4nrk4khgkxj78fcwwh6dl3uw4ep4tgu9q'
+      - '${THIS_IS_ALSO_AN_ENV_VAR}'
+    nodes:
+      - rpc: 'https://rpc-cosmos.endpoint.xyz/${SUPER_SECRET_TOKEN}'
+        api: 'https://lcd-cosmos.endpoint.xyz/${ANOTHER_ENV_VAR}'
+        grpc: 'grpc-cosmos.endpoint.xyz:9090'
+```
+
 ## Example: Supporting Custom Chain
 
 For devents, testnets, localnet even if unsupported mainnets, Use `custom_chains.yaml` for CVMS

internal/helper/config/config.go

@@ -3,6 +3,7 @@ package config
 import (
 	"fmt"
 	"os"
+	"regexp"
 	"strings"
 
 	"github.com/pkg/errors"
@@ -31,13 +32,35 @@ type NodeEndPoint struct {
 	GRPC string `yaml:"grpc"`
 }
 
+func replacePlaceholders(byteString []byte) []byte {
+	// Simple function to replace placeholders in the config file with their corresponding environment variables.
+	// Variables take the form of ${VAR_NAME}
+
+	// Convert the byte slice to a string
+	cfg := string(byteString)
+
+	// Regular expression to match placeholders in the format ${VAR_NAME}
+	re := regexp.MustCompile(`\$\{([a-zA-Z_][a-zA-Z0-9_]*)\}`)
+
+	cfg = re.ReplaceAllStringFunc(cfg, func(match string) string {
+		varName := re.FindStringSubmatch(match)[1]
+		if value, exists := os.LookupEnv(varName); exists {
+			return value
+		}
+		return match // return original placeholder if not found in environment variables
+	})
+	return []byte(cfg)
+}
+
 // TODO: ignore failed chains
 func GetConfig(path string) (*MonitoringConfig, error) {
 	dataBytes, err := os.ReadFile(path)
 	if err != nil {
 		return nil, errors.Wrapf(err, "failed to read config file")
 	}
 
+	dataBytes = replacePlaceholders(dataBytes)
+
 	cfg := &MonitoringConfig{}
 	err = yaml.Unmarshal(dataBytes, cfg)
 	if err != nil {

internal/helper/config/config_test.go

@@ -143,3 +143,49 @@ func TestGetSupportChainConfigForConsumerChains(t *testing.T) {
 		}
 	}
 }
+
+func TestReplacePlaceholders(t *testing.T) {
+	yamlCfg := `
+chains:
+  - display_name: "band"
+    chain_id: "laozi-mainnet"
+    monikers:
+      - "test"
+    nodes:
+      - rpc: "${RPC_NODE1}"
+        api: "${API_NODE1}"
+        grpc: "${GRPC_NODE1}"
+      - rpc: "${RPC_NODE2}"
+        api: "${API_NODE2}"
+        grpc: "${GRPC_NODE2}"
+`
+	envVars := map[string]string{
+		"RPC_NODE1":  "https://rpc.bandchain.org",
+		"API_NODE1":  "https://api.bandchain.org",
+		"GRPC_NODE1": "https://grpc.bandchain."}
+
+	envVarsNotSet := []string{
+		"RPC_NODE2",
+		"API_NODE2",
+		"GRPC_NODE2",
+	}
+
+	for key, value := range envVars {
+		os.Setenv(key, value)
+	}
+
+	replaceCfg := replacePlaceholders([]byte(yamlCfg))
+
+	replaceCfgStr := string(replaceCfg)
+
+	// test if unset palceholders were not replaced
+	for _, key := range envVarsNotSet {
+		assert.Contains(t, replaceCfgStr, fmt.Sprintf("${%s}", key))
+	}
+
+	// test if set palceholders were replaced
+	for key, value := range envVars {
+		assert.NotContains(t, replaceCfgStr, fmt.Sprintf("%s: %s", key, value))
+	}
+
+}