xds: only try to create an ipv6 expose checks listener if ipv6 is supported by the kernel

[rboyer]

Fixes #9311

This only fails if the kernel has ipv6 hard-disabled. It is not sufficient to merely not provide an ipv6 address for a network interface. For local testing I disabled it in grub on an ubuntu linux VM first.

Then register a service with connect locally with a config file like:

...
connect {
 sidecar_service {
  proxy {
   expose {
    checks = true
   }
  }
 }
}
...

Then try launching the sidecar and grep the envoy logs for the word expose

TODO

• add expose checks envoy integration test

[hashicorp-ci]

🤔 Double check that this PR does not require a changelog entry in the .changelog directory. Reference

[markan]

Looks good to me.

[markan]

@rboyer and I had a chat about testing; it's kind of thorny. Mocking this gets us into trouble with parallel unit tests, as we risk changing an invariant under other tests noses.

[rboyer]

The fake workloads are usually copies of fortio which has a webserver builtin. One of the pages is /debug so that'll 200, hence why it's used here as the healthcheck standin.

[rboyer]

Captured output from a run:

{
  "configs": [
    {
      "@type": "type.googleapis.com/envoy.admin.v3.BootstrapConfigDump",
      ...snip...
    },
    {
      "@type": "type.googleapis.com/envoy.admin.v3.ClustersConfigDump",
      ...snip...
    },
    {
      "@type": "type.googleapis.com/envoy.admin.v3.ListenersConfigDump",
      "version_info": "00000001",
      "dynamic_listeners": [
        {
          "name": "public_listener:0.0.0.0:21001",
          ...snip...
        },
        {
          "name": "exposed_path_debug:0.0.0.0:21500",
          "active_state": {
            "version_info": "00000001",
            "listener": {
              "@type": "type.googleapis.com/envoy.api.v2.Listener",
              "name": "exposed_path_debug:0.0.0.0:21500",
              "address": {
                "socket_address": {
                  "address": "0.0.0.0",
                  "port_value": 21500
                }
              },
              "filter_chains": [
                {
                  "filter_chain_match": {
                    "source_prefix_ranges": [
                      {
                        "address_prefix": "127.0.0.1",
                        "prefix_len": 8
                      },
                      {
                        "address_prefix": "127.0.0.1",
                        "prefix_len": 32
                      },
                      {
                        "address_prefix": "::1",
                        "prefix_len": 128
                      }
                    ]
                  },
                  "filters": [
                    {
                      "name": "envoy.http_connection_manager",
                      "config": {
                        "http_filters": [
                          {
                            "name": "envoy.router"
                          }
                        ],
                        "stat_prefix": "exposed_path_filter_debug_21500",
                        "route_config": {
                          "name": "exposed_path_filter_debug_21500",
                          "virtual_hosts": [
                            {
                              "routes": [
                                {
                                  "route": {
                                    "cluster": "local_app"
                                  },
                                  "match": {
                                    "path": "/debug"
                                  }
                                }
                              ],
                              "domains": [
                                "*"
                              ],
                              "name": "exposed_path_filter_debug_21500"
                            }
                          ]
                        },
                        "tracing": {
                          "random_sampling": {}
                        }
                      }
                    }
                  ]
                }
              ]
            },
            "last_updated": "2021-02-17T19:32:31.547Z"
          }
        }
      ]
    },
    {
      "@type": "type.googleapis.com/envoy.admin.v3.ScopedRoutesConfigDump"
    },
    {
      "@type": "type.googleapis.com/envoy.admin.v3.RoutesConfigDump",
      ...snip...
    },
    {
      "@type": "type.googleapis.com/envoy.admin.v3.SecretsConfigDump"
    }
  ]
}

[hashicorp-ci]

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[hashicorp-ci]

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