support absolute path redirects for location header in route config

Title: support absolute path redirects for location header in route config

Description:

Describe the desired behavior, what scenario it enables and how it would be used.

I asked a related question on the Slack.

Our users use our application at example.com, and we are using Envoy as a front proxy. It also sits behind Cloudflare and then on a K8S cluster with its own DNS name at prod.example.com.

We need to route our / landing page to /home for historical reasons. We used the following configuration:

          route_config:
            name: routes
            virtual_hosts:
            - name: service_routes
              domains:
              - "*"
              routes:
              # ... other routes
              - name: home redirect
                match:
                  path: "/"
                redirect:
                  path_redirect: "/home"

With this, I found out that Envoy will send a location header with the authority that Envoy resolved: prod.example.com.

I expected that the /home path redirect value would be returned directly. I think Envoy rewrites/upgrades the redirect to match what was incoming in the Host header, http/https.

I can mimic that behavior locally with a Host header, curl -v -H "Host: prod.example.com" http://localhost:5000:

proxy        | [2022-03-23 16:40:10.809][18][debug][conn_handler] [source/server/active_tcp_listener.cc:140] [C18] new connection from 172.24.0.1:62004
proxy        | [2022-03-23 16:40:10.811][18][debug][http] [source/common/http/conn_manager_impl.cc:283] [C18] new stream
proxy        | [2022-03-23 16:40:10.812][18][debug][http] [source/common/http/conn_manager_impl.cc:873] [C18][S17277694458725646929] request headers complete (end_stream=true):
proxy        | ':authority', 'prod.example.com'
proxy        | ':path', '/'
proxy        | ':method', 'GET'
proxy        | 'user-agent', 'curl/7.64.1'
proxy        | 'accept', '*/*'
proxy        |
proxy        | [2022-03-23 16:40:10.812][18][debug][http] [source/common/http/filter_manager.cc:841] [C18][S17277694458725646929] request end stream
proxy        | [2022-03-23 16:40:10.813][18][debug][lua] [source/extensions/filters/common/lua/lua.cc:39] coroutine finished
proxy        | [2022-03-23 16:40:10.813][18][debug][http] [source/common/http/filter_manager.cc:953] [C18][S17277694458725646929] Sending local reply with details direct_response
proxy        | [2022-03-23 16:40:10.813][18][debug][lua] [source/extensions/filters/common/lua/lua.cc:39] coroutine finished
proxy        | [2022-03-23 16:40:10.813][18][debug][http] [source/common/http/conn_manager_impl.cc:1472] [C18][S17277694458725646929] encoding headers via codec (end_stream=true):
proxy        | ':status', '301'
proxy        | 'location', 'http://prod.example.com/home'
proxy        | 'date', 'Wed, 23 Mar 2022 16:40:10 GMT'
proxy        | 'server', 'envoy'
proxy        |
proxy        | [2022-03-23 16:40:10.818][18][debug][connection] [source/common/network/connection_impl.cc:648] [C18] remote close
proxy        | [2022-03-23 16:40:10.818][18][debug][connection] [source/common/network/connection_impl.cc:249] [C18] closing socket: 0
proxy        | [2022-03-23 16:40:10.818][18][debug][conn_handler] [source/server/active_stream_listener_base.cc:120] [C18] adding to cleanup list

If Envoy returned the location header as an absolute path, there would be no inconsistency with http/https and user facing domain names.

I worked around this issue by adding host_redirect: example.com and https_redirect: true to the redirect config.

It would be great having absolute redirects without the rewrite/upgrade supported (returning Location: /home back to the user), or even simple url (https://example.com/home) driven redirects without needing multiple components defined in the config.

[optional Relevant Links:]

Any extra documentation required to understand the issue.

• Redirect Action
• Front proxy pattern

If you have alternative suggestions for approaches or title for this issue, please let me know.

Update

Tweaked the wording on the "worked around" line above.