Configuring CORS headers is essential when integrating Snowplow’s Scala Collector across multiple domains or frontend applications. In this post, we outline how to properly set CORS headers for the Scala Collector, ensuring secure data collection while maintaining cross-origin compatibility.

Q: What are CORS headers and why are they important?

Cross-Origin Resource Sharing (CORS) headers enable web applications to request resources from a different domain securely. In Snowplow’s Scala Collector, setting CORS headers correctly prevents data collection errors and ensures compatibility across multiple client applications.

Q: How do I configure CORS headers in the Scala Collector?

1. Locate the application.conf file:
   
   • The CORS settings are defined in the application.conf configuration file located in the Scala Collector directory.
     
     
2. Modify the CORS settings:
   
   • Adjust the cors section to include specific origins and headers. Example configuration:
     
     

cors {

  access-control-allow-origin = "*"

  access-control-allow-headers = ["Content-Type", "Origin", "Accept", "User-Agent"]

  access-control-allow-methods = ["GET", "POST", "OPTIONS"]

}

• Replace "*" with specific domains for stricter security:
  
  

access-control-allow-origin = "https://example.com"

3. Restart the Scala Collector:
   
   • Apply the new settings by restarting the Scala Collector:
     
     

sudo systemctl restart snowplow-collector

Q: How can I verify that CORS headers are applied correctly?

• Browser Developer Tools: Inspect the network requests in the browser to verify the presence of CORS headers.
  
  
• Curl Command:
  
  

curl -I -X OPTIONS https://your-collector-domain.com/com.snowplowanalytics.snowplow/tp2

• Check for Access-Control-Allow-Origin, Access-Control-Allow-Methods, and other relevant headers.
  
  

Q: What are common CORS configuration issues in Scala Collector?

• Missing Headers: Ensure that required headers like Content-Type and User-Agent are included.
  
  
• Wildcard Domain (*): Avoid using * in production; specify trusted domains to mitigate security risks.
  
  
• Incorrect Methods: Verify that required HTTP methods (e.g., POST, OPTIONS) are properly included in the CORS configuration.
  
  

Final Thoughts

Setting appropriate CORS headers in the Scala Collector is crucial for maintaining secure cross-domain data collection in Snowplow. By configuring these headers correctly, data engineers can prevent common CORS-related issues while ensuring robust tracking across multiple applications.

Stay tuned for further posts on Snowplow configuration best practices and troubleshooting techniques.