- Migrate `DOT` to `DNS_SERVER`
- Migrate `DOT_PROVIDERS` to `DNS_UPSTREAM_RESOLVERS`
- Migrate `DOT_PRIVATE_ADDRESS` to `DNS_PRIVATE_ADDRESSES`
- Migrate `DOT_CACHING` to `DNS_CACHING`
- Migrate `DOT_IPV6` to `DNS_UPSTREAM_IPV6`
- do not log dial error twice
- DNS subserver shuts down without waiting for connections to finish (UDP server would hang sometimes)
- DNS over TLS dialer uses tls.Dialer instead of wrapping connection with tls.Client
- connection type is just `tls` instead of `dns over tls` to reduce repetition in logs
- exchange errors contain the request question in their context
- Faster start up
- Clearer error messages
- Allow for more Gluetun-specific customization
- DNSSEC validation is dropped for now (it's sort of unneeded)
- Fix#137
- Better settings tree structure logged using `qdm12/gotree`
- Read settings from environment variables, then files, then secret files
- Settings methods to default them, merge them and override them
- `DNS_PLAINTEXT_ADDRESS` default changed to `127.0.0.1` to use DoT. Warning added if set to something else.
- `HTTPPROXY_LISTENING_ADDRESS` instead of `HTTPPROXY_PORT` (with retro-compatibility)
