# MediaTailor configuration aliases troubleshooting guide
<a name="configuration-aliases-troubleshooting"></a>

AWS Elemental MediaTailor provides systematic troubleshooting guidance for common configuration aliases issues and error scenarios. 

## Configuration alias validation errors
<a name="configuration-alias-validation-errors"></a>

When configuration aliases are missing or invalid, MediaTailor returns specific error responses to help identify the issue. 

**Common error scenarios**  
The following table describes common configuration alias errors and their resolution steps: 


| Error | Cause | Resolution | 
| --- | --- | --- | 
| HTTP 400: Invalid player parameter alias | Player parameter value not found in ConfigurationAliases | Verify that the player parameter value exists as a key in the corresponding ConfigurationAliases mapping | 
| HTTP 400: Missing required configuration alias | Domain variable used without corresponding ConfigurationAliases entry | Add the missing player parameter to ConfigurationAliases with all required alias mappings | 
| HTTP 400: Configuration validation failed | ConfigurationAliases structure is malformed or incomplete | Validate JSON structure and ensure all domain variables have corresponding aliases | 
| Empty string replacement in URLs | Non-domain variable alias not found | Add missing alias mapping or provide default value in ConfigurationAliases | 

**Validation checklist**  
Use the following checklist to validate your configuration aliases setup: 

1. **Domain variable coverage:** Ensure all variables used in domain portions of URLs have corresponding ConfigurationAliases entries

1. **Alias completeness:** Verify that all possible player parameter values are included as keys in the alias mappings

1. **JSON structure:** Validate that the ConfigurationAliases JSON is properly formatted and nested

1. **Parameter naming:** Confirm that all player parameters use the `player_params.` prefix

1. **Value consistency:** Ensure alias values are valid for their intended use (URLs, profile names, etc.)

## Debugging configuration alias resolution
<a name="configuration-alias-debugging"></a>

Follow this systematic approach to debug configuration alias resolution issues. 

**Step-by-step debugging methodology**  
Use the following steps to identify and resolve configuration alias issues: 

**Configuration alias debugging procedure**

1. **Verify configuration structure:** Confirm that your playback configuration includes properly formatted ConfigurationAliases

   ```
   {
       "ConfigurationAliases": {
           "player_params.example_param": {
               "alias1": "value1",
               "alias2": "value2"
           }
       }
   }
   ```

1. **Check player parameter format:** Ensure session initialization includes correctly formatted player parameters

   ```
   {
       "playerParams": {
           "example_param": "alias1"
       }
   }
   ```

1. **Validate alias mapping:** Confirm that the player parameter value ("alias1") exists as a key in the ConfigurationAliases mapping

1. **Test with simple configuration:** Start with a minimal configuration to isolate the issue

1. **Monitor error responses:** Check MediaTailor error responses for specific validation messages

1. **Verify resolved URLs:** Confirm that the final resolved URLs are valid and accessible

## Configuration aliases best practices
<a name="configuration-alias-best-practices"></a>

Follow these best practices to ensure reliable configuration alias implementation. 

**Security considerations**  
Implement the following security measures when you use configuration aliases: 
+ **Input validation:** Validate all player parameter values before using them in alias resolution
+ **Alias value sanitization:** Ensure alias values contain only expected characters and formats
+ **Domain restrictions:** Limit domain aliases to trusted, controlled domains
+ **Access control:** Restrict configuration modification to authorized personnel only

**Performance optimization**  
Optimize configuration alias performance with these recommendations: 
+ **Minimize alias count:** Use only necessary aliases to reduce processing overhead
+ **Efficient naming:** Use clear, consistent naming conventions for aliases and parameters
+ **Default values:** Provide sensible default aliases for common use cases
+ **Configuration caching:** Leverage MediaTailor's configuration caching for improved performance

**Maintenance and monitoring**  
Maintain reliable configuration alias operations with these practices: 
+ **Regular validation:** Periodically validate that all alias mappings are current and functional
+ **Error monitoring:** Monitor for HTTP 400 errors related to missing or invalid aliases
+ **Documentation:** Maintain clear documentation of all alias mappings and their purposes
+ **Testing procedures:** Implement comprehensive testing for all alias combinations