SNI dynamic forward proxy

Attention

SNI dynamic forward proxy support should be considered alpha and not production ready.

Through the combination of TLS inspector listener filter, this network filter and the dynamic forward proxy cluster, Envoy supports Server Name Indication (SNI) based dynamic forward proxy. The implementation works just like the HTTP dynamic forward proxy, but using the value in SNI as target host instead.

The following is a complete configuration that configures both this filter as well as the dynamic forward proxy cluster. Both filter and cluster must be configured together and point to the same DNS cache parameters for Envoy to operate as an SNI dynamic forward proxy.

Note

The following config doesn’t terminate TLS in listener, so there is no need to configure TLS context in cluster. The TLS handshake is passed through by Envoy.

admin:
  address:
    socket_address:
      protocol: TCP
      address: 127.0.0.1
      port_value: 9901
static_resources:
  listeners:
  - name: listener_0
    address:
      socket_address:
        protocol: TCP
        address: 0.0.0.0
        port_value: 10000
    listener_filters:
    - name: envoy.filters.listener.tls_inspector
      typed_config:
        "@type": type.googleapis.com/envoy.extensions.filters.listener.tls_inspector.v3.TlsInspector
    filter_chains:
    - filters:
      - name: envoy.filters.network.sni_dynamic_forward_proxy
        typed_config:
          "@type": type.googleapis.com/envoy.extensions.filters.network.sni_dynamic_forward_proxy.v3.FilterConfig
          port_value: 443
          dns_cache_config:
            name: dynamic_forward_proxy_cache_config
            dns_lookup_family: V4_ONLY
      - name: envoy.tcp_proxy
        typed_config:
          "@type": type.googleapis.com/envoy.extensions.filters.network.tcp_proxy.v3.TcpProxy
          stat_prefix: tcp
          cluster: dynamic_forward_proxy_cluster
  clusters:
  - name: dynamic_forward_proxy_cluster
    lb_policy: CLUSTER_PROVIDED
    cluster_type:
      name: envoy.clusters.dynamic_forward_proxy
      typed_config:
        "@type": type.googleapis.com/envoy.extensions.clusters.dynamic_forward_proxy.v3.ClusterConfig
        dns_cache_config:
          name: dynamic_forward_proxy_cache_config
          dns_lookup_family: V4_ONLY

Dynamic host and port selection

By default, the SNI dynamic forward proxy uses the SNI as target host, but it can be dynamically set by other network filters on a per-connection basis by setting a per-connection state object under the key envoy.upstream.dynamic_host. Additionally, the SNI dynamic forward proxy uses the default port filter configuration as target port, but it can by dynamically set, by setting a per-connection state object under the key envoy.upstream.dynamic_port. If these objects are set, they take precedence over the SNI value and default port. In case that the overridden port is out of the valid port range, the overriding value will be ignored and the default port configured will be used. See the implementation for the details.