Cloud Load Balancing - April 25th, 2025 [Deprecate]

## Deprecate **Starting April 28, 2025, the Global external Application Load Balancer and the Classic Application Load Balancer will no longer allow the use of custom request headers that reference connection-specific hop-by-hop headers.** **This change applies only to HTTP/1.1 traffic. Connection-specific hop-by-hop headers are already disallowed by the HTTP/2 and HTTP/3 protocols.** This change is in accordance with [RFC 2616](https://datatracker.ietf.org/doc/html/rfc2616#section-13.5.1) which states that these connection-specific hop-by-hop headers headers are meaningful only for a single transport-level connection and should not be forwarded by proxies. The impacted hop-by-hop headers are: `Connection`, `Keep-Alive`, `TE`, `Trailer`, `Transfer-Encoding`, and `Upgrade`. **Starting April 28, 2025**, connection-specific hop-by-hop headers that were configured by using custom headers will no longer be applied. These headers will only be set by the load balancer during normal connection handling. **Starting June 30, 2025**, any configuration changes that reference the connection-specific hop-by-hop custom headers will no longer be accepted. **What you need to do** If you are an HTTP/1.1 user affected by this change, complete the following steps: 1. Determine if your application depends on the values of any hop-by-hop headers configured as custom headers. If any dependencies are found, replace them with an allowed custom header and modify your application accordingly. 2. Review your backend service and URL map `headerAction` configuration to remove any references to connection-specific hop-by-hop headers.