route level http filter chain

[wbpcode]

Title: route level http filter chain

Description:
Now, http filter chain is defined in the HCM. We will iterate every filter in the chain for every request. But in some scenes, we may need different filters for different routes. For example, the route A may need buffer filter to be enabled, and the route B may only need cache filter to be enabled.

Although we provide composite filter as a delegator to enable/disable filter according to the headers matching, we need wrapper every filter by the composite filter and do the repeat matching.

May be we could add some new API (as followed) in the proto Route to enable or disable some filters in specificed route entry.

  message EnabledOrDisabledFilters {
    // Multiple filter names. Any name in the list MUST be one of :ref:`http filter names
    // <envoy_v3_api_field_extensions.filters.network.http_connection_manager.v3.HttpConnectionManager.http_filters>`.
    repeated string filters = 1;
    // If set to true, then all the filters referenced by the name in the ``filters`` will disabled in current route.
    bool disabled = 2;
  }

  EnabledOrDisabledFilters enabled_or_disabled_filters = 37;

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Any extra documentation required to understand the issue.

[wbpcode]

This would be a useful function for gateway/lb. Because they may have lots of routes and different routes may need different filters.

[wbpcode]

cc @mattklein123 @snowp

[zhxie]

I think every HTTP filters can use ExtensionWithMatcher to provide a filter selection (See Filter Integration). But you are right, if we have many filters which need to be selected, it will become a nervous work.

Instead of enabled_or_disabled_filters, I suggest adding a filter which works like a filter bundle,

- name: envoy.filters.network.http_connection_manager
  http_filters:
  - name: filter-1
  - name: filter-2
  - name: filter-bundle
    xds_matcher: /* some matcher*/
    http_filters:
      - filter-3
      - filter-4
  - name:  filter-5

[wbpcode]

@zhxie This is a way I have thinked about. However, for example, if we has ten different routes, then they may need different filters (an common scene in gateway), then we need created ten different filter bundle. And every request need to match this filter bundle repeatly to ensure if this filter bundle is enabled.

If we have thousands routes, then It would be very hard to maintain configuration like this and there would be lots of overhead of repeat matching.

Another problem is that because the matching conditions of the routes are not completely mutually exclusive, if this method is used, a request may match multiple filter bundles. So it's hard to implement "per route http filter chain" by this way.

[snowp]

May be we could add some new API (as followed) in the proto Route to enable or disable some filters in specificed route entry.

I think this could be implemented with minimal changes to the HCM/router: either the composite filter or something like it could be used to specify an optional filter which only applies if the per route config contains a specific entry/config. This way only optional filters have to evaluate whether or not they should be executed

FWIW my original design for composite filters allowed specifying multiple HTTP filters by integrating more closely with the FilterManager: instead of the current behavior where it delegates to an underlying filter implementation, it would inject the resulting filters from the match result into the list of filters. We moved away from this since it was more complicated than what we needed at the time, but might be something to reconsider here.

[snowp]

cc @htuch

[wbpcode]

an optional filter which only applies if the per route config contains a specific entry/config.

Yeah. We can design the new proto API first for the specific entry/config. And then we can iterate the implementation.

EnabledOrDisabledFilters is my initial idea for the new proto API.

[htuch]

Is this something we need a new Route feature for? Or can it just be per-route filter configuration?

[wbpcode]

cc @htuch It is a new Route feature used to tell that which http filters should be enabled for current route.

[github-actions]

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