EnvoyCon North America 2022

Envoy allows for modifying HTTP headers when sending requests upstream and responses downstream. The syntax used for creating header content is the same as for creating access log’s entry. But surprisingly, only a small subset of formatters were available for header modification compared to the full set of access log’s formatters. This has changed and now all formatters can be used in both, in header manipulation and in access logs. This talk describes logic used when creating access logs and when manipulating headers. It also explains why using the same formatter in the access log can render different results than using it in the header. Note: This feature is still under development, but I hope that it will be finished and merged to main before the conference. See https://github.com/envoyproxy/envoy/pull/21932