Support Centralized Proxy Configuration in `service-defaults`

Feature Description

Today you can configure Envoy proxy configuration both within a service instance and in the proxy-defaults/global configuration entry. The protocol configuration can also be set within the service-defaults configuration entry. Other configurations like local_request_timeout_ms and local_connect_timeout_ms cannot be set here.

The feature request is to support setting some of these configurations within the service-defaults config entry. However some others such as the bind_address probably don't make sense to set centrally so its not quite so simple as just merge an extra config source.

Use Case(s)

I encountered a gRPC API where the local app could take several minutes to return data for a specific API. I had wanted to set local_request_timeout_ms for all instances of the service but it wasn't possible. I had to resort to configuring by modifying all instances of the service.

Food for Thought

If an application is configured with a local_request_timeout_ms value, would it be a good idea to auto-propagate this timeout to consumers/downstreams of that service. That way we don't have to configure the timeout in 2 different places. Maybe downstreams would want to timeout sooner. In that case they could specify the timeout and this would just be a way to modify the default timeout value.

Hi, @mkeeler , I am interested in implementing this feature and would like to give it a shot. Could you help clarify the following questions regarding the new feature?

In the definition of service-defaults, there is a similar instance-level field, named MaxInboundConnections. It seems to me that the local_request_timeout_ms and local_connect_timeout_ms should be in the same level as MaxInboundConnections. So the modified struct will look like

type ServiceConfigEntry struct {
    // omitted fields
    MaxInboundConnections int
+    LocalConnectTimeOut int
+   LocalRequestTimeOut int
}

What do you think?

It seems that most of the dynamic configurations has already been added to the service-default. Is there any other fields we need to consider with these 2?
The fields appear in the service definition as follows (in the order of precedence):

Individual service instance (which I think is already available since you can manually apply the configuration to each instance)

service {
  name    = "B"
  id      = "B-id-1"
  connect {
    sidecar_service {
      proxy {
        config {
          max_inbound_connections = 100
          local_connect_timeout_ms = 20000  // 20s; override the timemout from service-defaults
          local_request_timeout_ms = 60000  // 60s; override the timemout from service-defaults
        }
        upstreams = [
          {
            destination_name   = "C"
            config {
              limits {
                max_connections         = 200
              }
            }
          }
        ]
      }
    }
  }

in service-defaults (to be added)

Kind = "service-defaults"
Name = "B"

Config {
    local_connect_timeout_ms = 10000  // 10s; change default  local_connect_timeout_ms
    local_request_timeout_ms = 20000  // 20s; change default  local_request_timeout_ms
}

UpstreamConfig = {
  Defaults = {
    Limits = {
      MaxConnections = 512
      MaxPendingRequests = 512
      MaxConcurrentRequests = 512
    }
  }
}

At proxy-defaults (already available)

Kind      = "proxy-defaults"
Name      = "global"
Config {
  local_connect_timeout_ms = 1000
  local_request_timeout_ms = 20000 
  max_connections         = 200
}

Thanks in advance.

hashicorp / consul