enable a disabled filter by complete empty config or meaningless placeholder in the route

[wbpcode]

Now, we can mark a filter in the HTTP filter chain as disabled by default and enable it by a valid route per filter config in the route/vh. See the following example. The filter lua will be disabled by default and be skipped when creating HTTP filter chain instance, except it's re-enabled by a valid route config in specific route. By this way, we can achieve the target of configuring route specific HTTP filter chain. Different route could have different HTTP filter chain.

  http_filters:
  - name: buffer
    typed_config: { ... }
    disabled: true
  - name: lua
    typed_config: { ... }
    disabled: true


  typed_per_filter_config:
    lua:
      "@type": type.googleapis.com/envoy.extensions.filters.http.lua.v3.LuaPerRoute
      name: my_lua_script

However, there two special case that haven't been handled appropriately:

• A filter may have no a route level config definition but also wants this feature.
• A filter may just want to enable the filter but doesn't want to provide any route override config.

[wbpcode]

cc @adisuissa @envoyproxy/api-shepherds

[wbpcode]

There are some possible solutions:

1. Hack of current FilterConfig. This is supported and works, but far off from good. We can config an arbitrary proto config in the FilterConfig and set the is_optional to true. Then Envoy will accept this config and treat is an enable flag.

  typed_per_filter_config:
    lua:
      "@type": type.googleapis.com/envoy.config.route.v3.FilterConfig
      config: # Note this config field could not be empty because the xDS API requirement.
        "@type": type.googleapis.com/google.protobuf.Empty  # Empty as a placeholder.
      is_optional: true

2. Make the google.protobuf.Emtpy as special placeholder and without setting the is_optional field. This need additional development to support this logic.

  typed_per_filter_config:
    lua:
      "@type": type.googleapis.com/envoy.config.route.v3.FilterConfig
      config: # Note this config field could not be empty because current validation.
        "@type": type.googleapis.com/google.protobuf.Empty  # Empty as a placeholder.

3. Accept empty config field, and treat FilterConfig that has no any field be set as enable flag. This need additional development to remove current validation.

  typed_per_filter_config:
    lua:
      "@type": type.googleapis.com/envoy.config.route.v3.FilterConfig

4. Like 2 but define a new message as placeholder to avoid using google.protobuf.Empty. This need additional development to support this logic.

  typed_per_filter_config:
    lua:
      "@type": type.googleapis.com/envoy.config.route.v3.FilterConfig
      config:
        "@type": type.googleapis.com/envoy.config.route.v3.Placeholder

[adisuissa]

Two other options:

1. Add an enabled/override_disabled field in FilterConfig to override the disabled flag.
2. Add an external enable_per_config with a set (repeated) of names of filters to enable (less likely IMHO).

[github-actions]

This issue has been automatically marked as stale because it has not had activity in the last 30 days. It will be closed in the next 7 days unless it is tagged "help wanted" or "no stalebot" or other activity occurs. Thank you for your contributions.

[marc-barry]

I ran into the same need in #33791 as #33791 (comment) suggested 1. from #31482 (comment). I was unable to get this to work at this time. I think that #33791 (comment) and #33791 (comment) are what 1. is suggesting.

[wbpcode]

@marc-barry check the latest comment #33791 (comment) :)

[marc-barry]

@marc-barry check the latest comment #33791 (comment) :)

For those of you who encounter this issue #33791 (comment) did work as suggested and was a solution to suit my needs.