The /etc/envoy/envoy.yaml is not marked as a config file in the deb packages, which means that updating the package unconditionally overwrites the file.
user@server:/var/lib/dpkg/info$ apt-cache policy envoy | head -2
envoy:
Installed: 1.36.6
user@server:/var/lib/dpkg/info$ cat envoy.list
/etc
/etc/envoy
/etc/envoy/envoy.yaml
/usr
/usr/bin
/usr/bin/envoy
/usr/share
/usr/share/doc
/usr/share/doc/envoy
/usr/share/doc/envoy/copyright
user@server:/var/lib/dpkg/info$ cat envoy.conffiles
cat: envoy.conffiles: No such file or directory
user@server:/var/lib/dpkg/info$
The
/etc/envoy/envoy.yamlis not marked as a config file in the deb packages, which means that updating the package unconditionally overwrites the file.