Logs: disable invalid upstream warning when api_backend is null and e…

[tkan145]

What

Fix https://issues.redhat.com/browse/THREESCALE-5225

PR #1285 only handles the case where api_backend is nil, however, when api_backend is set to an empty string or null json value, the warning log can still be seen in the log.

Verification steps:

• Create a apicast-config.json file with the following content

cat <<EOF >apicast-config.json
{
  "services": [
    {
      "backend_version": "1",
      "id": "1",
      "api_backend": null,
      "proxy": {
        "api_backend": null,
        "service_backend_version": "1",
        "hosts": [
          "one"
        ],
        "backend": {
          "endpoint": "http://127.0.0.1:8081",
          "host": "backend"
        },
        "policy_chain": [
          {
            "name": "apicast.policy.routing",
            "version": "builtin",
            "enabled": true,
            "configuration": {
              "rules": [
                {
                  "url": "https://echo-api.3scale.net:443",
                  "replace_path": "{{uri | remove_first: '/test'}}",
                  "owner_type": "BackendApi",
                  "condition": {
                    "operations": [
                      {
                        "match": "path",
                        "op": "matches",
                        "value": "^(/test/.*|/test/?)"
                      }
                    ]
                  }
                }
              ]
            }
          },
          {
            "name": "apicast.policy.apicast"
          }
        ],
        "proxy_rules": [
          {
            "http_method": "GET",
            "pattern": "/",
            "metric_system_name": "hits",
            "delta": 1,
            "parameters": [],
            "querystring_parameters": {}
          }
        ]
      }
    }
  ]
}
EOF

• Checkout this branch and start dev environment

make development
make dependencies

• Run apicast locally

THREESCALE_DEPLOYMENT_ENV=staging APICAST_LOG_LEVEL=warn APICAST_WORKER=1 APICAST_CONFIGURATION_LOADER=lazy APICAST_CONFIGURATION_CACHE=0 THREESCALE_CONFIG_FILE=apicast-config.json ./bin/apicast

• Capture apicast IP

APICAST_IP=$(docker inspect apicast_build_0-development-1 | yq e -P '.[0].NetworkSettings.Networks.apicast_build_0_default.IPAddress' -)

• Send a request

curl -i -k -H "Host: one" "http://${APICAST_IP}:8080/test?user_key="

• The response should be HTTP/1.1 200

< HTTP/1.1 200 OK
< Server: openresty
< Date: Thu, 22 Feb 2024 01:44:59 GMT
< Content-Type: application/json
< Content-Length: 564
< Connection: keep-alive
< x-3scale-echo-api: echo-api/1.0.3
< vary: Origin
< x-content-type-options: nosniff
< x-envoy-upstream-service-time: 0

Check that apicast.lua:65: upstream api for the service:1 is invalid, error:Upstream cannot be null, client: XX.XXX.X is not visible in logs

[tkan145]

Rebased on top of master. @eguzki this one is ready for review

[eguzki]

verification steps worked

[eguzki]

why do you add a new space? Could be unintended change?

[tkan145]

My editor auto format file on save 😓 . Fixed.

Since I've introduced a new change, I'll need another approval.