HTTPFault abort filter doesn't work as expected on route typed_per_filter_config

[Austin Guo]

Hey Envoy team!

I'm trying to use the abort HTTPFault HTTP filter override configured on an Envoy Route via typed_per_filter_config. For some reason the HTTPFault filter does not work as expected. I see the following behavior:

• When the Envoy Route does not have a typed_per_filter_config, no requests are aborted as expected.
• When the Envoy Route has the typed_per_filter_config set at 100% abort, all requests are aborted as expected
• BUT when the Envoy Route has the typed_per_filter_config set at 50% abort, 99.94% of requests are still aborted. I've tested this with 10k requests multiple times, so I don't think I ran into a statistical anomaly

Is there perhaps a bug with using HTTPFault abort filter via typed_per_filter_config? I'm using Envoy version 7b292c7175692c822148b64005a731eb00365508/1.28.1-dev/Clean/RELEASE/BoringSSL

The configuration I'm using on the route is

```
  "typed_per_filter_config": {
    "envoy.filters.http.fault": {
      "@type": "type.googleapis.com/envoy.extensions.filters.http.fault.v3.HTTPFault",
      "abort": {
        "http_status": 503,
        "percentage": {
          "numerator": 50
        }
      },
      "filter_metadata": {
        "reason": "<redacted>"
      }
    }
  },

```

and I have a corresponding listener filter named envoy.filters.http.fault

```
                          {
                            "name": "envoy.filters.http.fault",
                            "typed_config": {
                              "@type": "type.googleapis.com/envoy.extensions.filters.http.fault.v3.HTTPFault"
                            }
                          },

```

As far as I know, the HTTPFault configuration has the correct schema.

Any help would be much appreciated.

Best,

Austin

[Austin Guo]

Does this maybe have something to do with client connection reuse? I notice that when I curl the test service directly, I get approximately 50% aborted. but if I use python requests.Session, I get close to 100% aborted.

[Austin Guo]

I've figured out the issue, it was an issue with my own test environment setup. Everything looks correct now. Thanks for all the help!