there are some issues with the python requirements of envoy 1.16.2 as it requires python 3.6 or higher and clearly the building environment isn't fulfilling the requirement. So a tiny workaround is required to build 1.16.2 on builder-envoy-03:

generating docs...
Traceback (most recent call last):
  File "tools/dependency/validate_test.py", line 6, in <module>
    import validate
  File "/source/tools/dependency/validate.py", line 90
    deps_query = ' union '.join(f'deps({l})' for l in targets)
                                           ^
SyntaxError: invalid syntax

diff --git a/ci/do_ci.sh b/ci/do_ci.sh
index bda21807..526aa839 100755
--- a/ci/do_ci.sh
+++ b/ci/do_ci.sh
@@ -411,8 +411,8 @@ elif [[ "$CI_TARGET" == "fix_spelling_pedantic" ]]; then
 elif [[ "$CI_TARGET" == "docs" ]]; then
   echo "generating docs..."
   # Validate dependency relationships between core/extensions and external deps.
-  tools/dependency/validate_test.py
-  tools/dependency/validate.py
+#  tools/dependency/validate_test.py
+#  tools/dependency/validate.py
   # Build docs.
   BAZEL_BUILD_OPTIONS="${BAZEL_BUILD_OPTIONS[*]}" docs/build.sh
   exit 0

@Vgutierrez we can create a new building env based on buster I think, that's much better as an option.

I suggest to activate configuration option
accept_http_10
(bool) Handle incoming HTTP/1.0 and HTTP 0.9 requests. This is off by default, and not fully standards compliant. There is support for pre-HTTP/1.1 style connect logic, dechunking, and handling lack of client host iff
because php function file_get_contents() uses protocol http/1.0

Envoy seems to be on 1.18.2 now. Can this be closed, or was there any other deployment need this ticket addresses?

AFAIK this was only impacting envoy as the TLS terminator of the CDN and we went with HAProxy so this can be closed