thoughts on calling this circuitBreaker ?

Yea, Connection is a very vague name... I think that CircuitBreaker implies that some sort of failure or unexpected degradation in service triggers the blocking behavior, which isn't really the case here. WDYT about Resources or Limits?

isn't this the same as https://gateway.envoyproxy.io/latest/user/circuit-breaker/
I'm not tied to a specific name, but hoping both downstream and upstream use the same name e.g. connectionPool

Some examples of how this feature is named in other products:

• Nginx: limit_conn - https://nginx.org/en/docs/http/ngx_http_limit_conn_module.html
• Kemp: client connection limiter (this is actually more of a connection rate limiter than a total connection limiter) - https://support.kemptechnologies.com/hc/en-us/articles/115004547103-How-To-Limit-The-Number-Of-Connections-Per-Second-From-A-Specific-Host
• HAProxy: maxconn - https://www.haproxy.com/documentation/haproxy-configuration-manual/latest/#maxconn
• Traefik: InFlightConn - https://doc.traefik.io/traefik/v3.0/middlewares/tcp/inflightconn/
• F5: Connection Limits - https://techdocs.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/ltm-implementations-13-1-0/25.html
• Gloo Edge: ConnectionLimits- https://docs.solo.io/gloo-edge/main/guides/security/limit-connection/

So, I feel that Connection[Limits|Settings|Options] is a pretty intuitive name for a container which can also include other settings from the timeout and circuit breaker domains. However, not everything is symmetric, due to missing envoy functionality.

connectionSettings:
  maxParallelConnections: 10000 # *[CircuitBreaker;Symmetric]* Total active connections
  maxNewConnectionsPerSecond: 100 # [NEW;Downstream] CPS rate limit, in theory such a rate limit can also be implemented for clusters, but is not supported today
  maxConnectionBufferSize: 100kb # *[NEW;Symmetric]* per connection memory allocation
  maxConnectionIdleTime: 600s # *[Timeout; Symmetric]*
  maxConnectTime: 10s # *[Timeout; Symmetric]* time to establish a connection
  http:
    maxRequestsPerConnection: 5000 # *[CircuitBreaker; Symmetric]* close connection after this amount of request
    maxConnectionDuration: 3600s # *[CircuitBreaker; Symmetric]* close connection after this duration
    maxParallelRequests: 1000 # *[CircuitBreaker; Upstream]*  No envoy downstream equivalent that I know of, but could maybe be implemented through a simplified concurrency controller for adaptive concurrency filter. https://www.envoyproxy.io/docs/envoy/latest/configuration/http/http_filters/adaptive_concurrency_filter#concurrency-controllers). 
    maxPendingRequest: 500 # *[CircuitBreaker; Upstream]* only for upstream, don't think that it makes sense for envoy to queue downstream requests... 

thanks for doing the research !
I'm on board with the top level connection field now :)
my only follow up since limit is not a struct but a value, how do we expose the delay knob, which is useful to thwart ddos

thoughts on value ? , else connections.limi.maxActiveConnections seems repetitive ...